Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the star cluster known as Messier 73.
During the 18th century, famed French astronomer Charles Messier noticed the presence of several “nebulous objects” while surveying the night sky. Originally mistaking these objects for comets, he began to catalog them so that others would not make the same mistake. Today, the resulting list (known as the Messier Catalog) includes over 100 objects and is one of the most influential catalogs of Deep Space Objects.
One of these objects is Messier 73, a four star asterism located approximately 2,500 light-years from Earth. It is visible in the southern part of the Aquarius constellation, near the border of Capricornus and just southeast of Messier 72. Given that Aquarius and Capricornus are relatively faint constellations, this object is one of the more challenging Messier objects to find in the night sky. Continue reading “Messier 73 – the NGC 6994 Star Cluster”
Hubble image of the intermediate spiral galaxy known as Messier 65, which is located in the Leo constellation. Credit: ESA/Hubble & NASA
Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at the intermediate spiral galaxy known as Messier 65.
In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects he initially mistook for comets. In time, he would come to compile a list of approximately 100 of these objects, hoping to prevent other astronomers from making the same mistake. This list – known as the Messier Catalog – would go on to become one of the most influential catalogs of Deep Sky Objects.
One of these objects is the intermediate spiral galaxy known as Messier 65 (aka. NGC 3623), which is located about 35 million light-years from Earth in the Leo constellation. Along with with Messier 66 and NGC 3628, it is part of a small group of galaxies known as the Leo Triplet, which makes it one of the most popular targets among amateur astronomers.
Description:
Enjoying life some 35 million light years from the Milky Way, the group known as the “Leo Trio” is home to bright galaxy Messier 65 – the westernmost of the two M objects. To the casual observer, it looks like a very normal spiral galaxy and thus its classification as Sa – but M65 is a galaxy which walks on the borderline. Why? Because of close gravitational interaction with its nearby neighbors. Who can withstand the draw of gravity?!
The Messier 65 intermediate spiral galaxy. Credit: ESO/INAF-VST/OmegaCAM/Astro-WISE/Kapteyn Institute
Chances are very good that Messier 65 is even quite a bit larger than we see optically as well. As E. Burbidge (et al) said in a 1961 study:
“A fragmentary rotation-curve for NGC 3623 was obtained from measures of the absorption features Ca ii X 3968 and Na I X 5893 and the emission lines [N ii] X 6583 and Ha. The measures from two outer regions are discordant if only circular velocities are assumed, and it is concluded that the measured velocity of one of these regions-the only prominent H ii region in the galaxy-has a large non-circular component. The approximate mass derived from the velocity in the outer arm relative to the center is 1.4 X 1011 M0. It is concluded that the total mass is larger than this, perhaps between 2 and 3 X 1011 M0. This would suggest that the mass-to-light ratio in solar units (photographic) for this galaxy, which is intermediate in type between Sa and Sb, lies between 10 and 20.”
But just how much interaction has been going on between the three galaxies which coexist so closely? Sometimes it takes things like studying in multicolor photometry data to understand. As Zhiyu Duan of the Chinese Academy of Sciences Astronomical Observatory indicated in a 2006 study:
“By comparing the observed SEDs of each part of the galaxies with the theoretical ones generated by instantaneous burst evolutionary synthesis models with different metallicities (Z = 0.0001, 0.008, 0.02, and 0.05), two-dimensional relative age distribution maps of the three galaxies were obtained. NGC 3623 exhibits a very weak age gradient from the bulge to the disk. This gradient is absent in NGC 3627. The ages of the dominant stellar populations of NGC 3627 and NGC 3628 are consistent, and this consistency is model independent (0.5-0.6 Gyr, Z = 0.02), but the ages of NGC 3623 are systematically older (0.7-0.9 Gyr, Z = 0.02). The results indicate that NGC 3627 and NGC 3628 have undergone synchronous evolution and that the interaction has likely triggered starbursts in both galaxies. The results indicate that NGC 3627 and NGC 3628 have undergone synchronous evolution and that the interaction has likely triggered starbursts in both galaxies. For NGC 3623, however, the weak age gradient may indicate recent star formation in its bulge, which has caused its color to turn blue. Evidence is found for a potential bar existing in the bulge of NGC 3623, and my results support the view that NGC 3623 does interact with NGC 3627 and NGC 3628.”
Messier 65, as imaged by the Hubble Space Telescope. Credit: NASA,/ESA/Hubble Space Telescope
So, let’s try looking at things in a slightly different color – integral-field spectroscopy. As V.L. Afanasiev (et al) said in a 2004 study:
“The mean ages of their circumnuclear stellar populations are quite different, and the magnesium overabundance of the nucleus in NGC 3627 is evidence for a very brief last star formation event 1 Gyr ago whereas the evolution of the central part of NGC 3623 looks more quiescent. In the center of NGC 3627 we observe noticeable gas radial motions, and the stars and the ionized gas in the center of NGC 3623 demonstrate more or less stable rotation. However, NGC 3623 has a chemically distinct core – a relic of a past star formation burst – which is shaped as a compact, dynamically cold stellar disk with a radius of ?250-350 pc which has been formed not later than 5 Gyr ago.”
Now, let’s take a look at that gas – and the properties for the gases that exist and co-exist in the galactic trio. As David Hogg (et al) explained in a 2001 study:
“We have studied the distribution of cool, warm, and hot interstellar matter in three of the nearest bright Sa galaxies. New X-ray data for NGC 1291, the object with the most prominent bulge, confirm earlier results that the ISM in the bulge is dominated by hot gas. NGC 3623 has a lesser amount of hot gas in the bulge but has both molecular gas and ionized hydrogen in the central regions. NGC 2775 has the least prominent bulge; its X-ray emission is consistent with an origin in X-ray binary stars, and there is a strict upper limit on the amount of molecular present in the bulge. All three galaxies have a ring of neutral hydrogen in the disk. NGC 3623 and NGC 2775 each have in addition a molecular ring coincident with the hydrogen ring. We conclude that even within the morphological class Sa there can be significant differences in the gas content of the bulge, with the more massive bulges being likely to contain hot, X-ray–emitting gas. We discuss the possibility that the X-ray gas is part of a cooling flow in which cool gas is produced in the nucleus.”
The Leo Triplet, with M65 at the upper right, M66 at the lower right, and NGC 3628 at the upper left. Credit: Scott Anttila. Credit: Wikipedia Commons/Anttler
Even more studies have been done to take a look a disc properties associated with M65. According to M. Bureau (et al);
“NGC 3623 (M 65) is another highly-inclined galaxy in the Leo group, but it is of much later type than NGC 3377, SABa(rs). It is part of the Leo triplet with NGC 3627 and NGC 3628 but does not appear to be interacting. NGC 3623’s kinematics an has barely been studied and observations provide a glimpse of its dynamics. The large-scale velocity reveals minor-axis rotation, in agreement with the presence of a bar. In addition, a quasi edge-on disk is present in the center, where the iso velocity contours flatten out abruptly.”
History of Observation:
Both M65 and M66 were discovered on the same night – March 1, 1780 – by Charles Messier, who described M65 as “Nebula discovered in Leo: It is very faint and contains no star.” Sir William Herschel would later observe M65 as well, describing it as “A very brilliant nebula extended in the meridian, about 12′ long. It has a bright nucleus, the light of which suddenly diminishes on its border, and two opposite very faint branches.”
However, it would be Lord Rosse who would be the first to see structure: “March 31, 1848. – A curious nebula with a bright nucleus; resolvable; a spiral or annular arrangement about it; no other portion of the nebula resolved. Observed April 1, 1848 and April 3, with the same results.”
Locating Messier 65:
Even though you might think by its apparent visual magnitude that M65 wouldn’t be visible in small binoculars, you’d be wrong. Surprisingly enough, thanks to its large size and high surface brightness, this particular galaxy is very easy to spot directly between Iota and Theta Leonis. In even 5X30 binoculars under good conditions you’ll easy see both it and M66 as two distinct gray ovals.
Messier 65 location. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)
A small telescope will begin to bring out structure in both of these bright and wonderful galaxies, but to get a hint at the “Trio” you’ll need at least 6″ in aperture and a good dark night. If you don’t spot them right away in binoculars, don’t be disappointed – this means you probably don’t have good sky conditions and try again on a more transparent night. The pair is well suited to modestly moonlit nights with larger telescopes.
Capture one of the Trio tonight! And here are the quick facts on this Messier Object:
Object Name: Messier 65 Alternative Designations: M65, NGC 3623, (a member of the) Leo Trio, Leo Triplet Object Type: Type Sa Spiral Galaxy Constellation: Leo Right Ascension: 11 : 18.9 (h:m) Declination: +13 : 05 (deg:m) Distance: 35000 (kly) Visual Brightness: 9.3 (mag) Apparent Dimension: 8×1.5 (arc min)
Image of the Black Eye Galaxy (Messier 64), taken with Hubble's Wide Field Planetary Camera 2 (WFPC2). Credit: NASA and The Hubble Heritage Team (AURA/STScI)
Welcome back to Messier Monday! Today, we continue in our tribute to our dear friend, Tammy Plotner, by looking at that “evil” customer known as Messier 64 – aka. the “Black Eye Galaxy”!
In the 18th century, while searching the night sky for comets, French astronomer Charles Messier kept noting the presence of fixed, diffuse objects he initially mistook for comets. In time, he would come to compile a list of approximately 100 of these objects, hoping to prevent other astronomers from making the same mistake. This list – known as the Messier Catalog – would go on to become one of the most influential catalogs of Deep Sky Objects.
One of these objects is known as Messier 64, which is also known as the “Black Eye” or “Evil Eye Galaxy”. Located in the Coma Berenices constellation, roughly 24 million light-years from Earth, this spiral galaxy is famous for the dark band of absorbing dust that lies in front of the galaxy’s bright nucleus (relative to Earth). Messier 64 is well known among amateur astronomers because it is discernible with small telescopes.
Description:
Residing about 19 million light years from our home galaxy, the “Sleeping Beauty” extends across space covering an area nearly 40,000 light years across, spinning around at a speed of 300 kilometers per second. Toward its core is a counter-rotating disc approximate 4,000 light years wide and the friction between these two may very well be the contributing factor to the huge amounts of starburst activity and distinctive dark dust lane.
Infrared image taken by the Hubble Space Telescope, which penetrated the dust clouds swirling around the centers of the M64 galaxy. Credits: Torsten Boeker, Space Telescope Science Institute and NASA/ESA
Stars themselves appear to be forming in two waves, first evolving outside following the density gradient where abundant interstellar matter was waiting, and then evolving slowly. As the material from the mature stars began beig pushed back by their stellar winds, supernovae, and planetary nebulae, increased amounts of interstellar matter once again compressed, beginning the process of star formation again. This “second wave” may very well be represented by the dark, obscuring dust lane we see.
But, M64 isn’t without it share of turmoil. Its dual rotation may have started as a collision when two galaxies merged some billion years ago – or so theory would suggest. But did it? As Robert Braun and Rene Walterbos explained in their 1995 study:
“This galaxy is known to contain two nested, counter rotating, gas disks of a few 108 solar mass each, with the inner disk extending to approximately 1 kpc and the outer disk extending beyond. The stellar kinematics along the major axis, extending across the transition region between the two gas disks, show no hint of velocity reversal or increased velocity dispersion. The stars always rotate in the same sense as the inner gas disk, and thus it is the outer disk which ‘counterrotates’. The projected circular velocities inferred from the stellar kinematics and from the H I disks agree to within approximately 10 km/s, supporting other evidence that the stellar and gaseous disks are coplanar to approximately 7 deg. This upper limit is comparable to the mass of detected counter rotating gas. This low mass of counter rotating material, combined with the low-velocity dispersion in the stellar disk, implies that NGC 4826 cannot be the product of a retrograde merger of galaxies, unless they differed by at least an order of magnitude in mass. The velocities of the ionized gas along the major axis are in agreement with that of the stars for R less than 0.75 kpc. The subsequent transition toward apparent counter rotation of the ionized gas is spatially well resolved, extending over approximately 0.6 kpc in radius. The kinematics of this region are not symmetric with respect to the galaxy center. On the southeast side there is a significant region in which vproj (H II) much less than vcirc approximately 150 km/s, but sigma (H II) approximately 65 km/s. The kinematic asymmetries cannot be explained with any stationary dynamical model, even is gas inflow or warps were invoked. The gas in this transition region shows a diffuse spatial structure, strong (N II) and (S II) emission, as well as the high-velocity dispersion. These data present us with the conundrum of explaining a galaxy in which a stellar disk, and two counter rotating H I disks, at smaller and much larger radii, appear in equilibrium and nearly coplanar, yet in which the transition region between the gas disks is not in steady state.”
So is all what it really appears to be? Are new stars being born in the darkness? As A. Majeed (et al) indicated in their 1999 study:
“The Evil Eye galaxy (NGC 4826; M64) is distinguished by an asymmetrically placed, strongly absorbing dust lane across its prominent bulge. We obtained a long-slit spectrum of NGC 4826, with the slit across the galaxy’s nucleus, covering equal parts of the obscured and the unobscured portions of the bulge. By comparing the spectral energy distributions at corresponding positions on the bulge, symmetrically placed with respect to the nucleus, we were able to study the wavelength dependent effects of absorption, scattering, and emission by the dust, as well as the presence of ongoing star formation in the dust lane. We report the detection of strong extended red emission (ERE) from the dust lane within about 15 arcsec distance from the nucleus of NGC 4826. The ERE band extends from 5400 A to 9400 A, with a peak near 8800 A. The integrated ERE intensity is about 75 % of that of the estimated scattered light from the dust lane. The ERE shifts toward longer wavelengths and diminishes in intensity as a region of star formation, located beyond 15 arcsec distance, is approached. We interpret the ERE as originating in photoluminescence by nanometer-sized clusters, illuminated by the galaxy’s radiation field, in addition to the illumination by the star-forming complex within the dust lane. When examined within the context of ERE observations in the diffuse ISM of our Galaxy and in a variety of other dusty environments such as nebulae, we conclude that the ERE photon conversion efficiency in NGC 4826 is as high as found elsewhere, but that the size of the nanoparticles in NGC 4826 is about twice as large as those thought to exist in the diffuse ISM of our Galaxy.”
Messier 64 (“Black Eye Galaxy”) imaged using amateur telescope. Credit: Jeff Johnson.
But the debate is still on. As R.A. Walterbos (et al) expressed in their 1993 study:
“The close to coplanar orientation of the gas disks is one aspect which is in good agreement with what is expected on the basis of a merger model for the counter-rotating gas. The rotation direction of the inner gas disk with respect to the stars, however, is not. In addition, the existence of a well defined exponential disk probably implies that if a merger did occur it must have been between a gas-rich dwarf and a spiral, not between two equal mass spirals. The stellar spiral arms of NGC 4826 are trailing over part of the disk and leading in the outer disk. Recent numerical calculations by Byrd et al. for NGC 4622 suggest that long lasting leading arms could be formed by a close retrograde passage of a small companion. In this scenario, the outer counter-rotating gas disk in NGC 4826 might be the tidally stripped gas from the dwarf. However, in NGC 4826 the outer arms are leading, while it appears that in NGC 4622 the inner arms are leading. A realistic N-body/hydro simulation of a dwarf-spiral encounter is clearly needed. It may also be possible that the counter-rotating outer gas disk is due to gradual infall of gas from the halo, rather than from a discrete merger event.”
History of Observation:
M64 was discovered by Edward Pigott on March 23, 1779, just 12 days before Johann Elert Bode found it independently on April 4, 1779. Roughly a year later, Charles Messier independently rediscovered it on March 1, 1780 and cataloged it as M64. Said Pigot:
“.. on the 23rd of March [1779], I discovered a nebula in the constellation of Coma Berenices, hitherto, I presume, unnoticed; at least not mentioned in M. de la Lande’s Astronomy, nor in M. Messier’s ample Catalogue of nebulous Stars [of 1771]. I have observed it in an acromatic instrument, three feet long, and deduced its mean R.A. by comparing it to the following stars Mean R.A. of the nebula for April 20, 1779, of 191d 28′ 38″. Its light being exceedingly weak, I could not see it in the two-feet telescope of our quadrant, so was obliged to determine its declination likewise by the transit instrument. The determination, however, I believe, may be depended upon to two minutes: hence, the declination north is 22d 53″1/4. The diameter of this nebula I judged to be about two minutes of a degree.”
However, Pigott’s discovery got published only when read before the Royal Society in London on January 11, 1781, while Bode’s was published during 1779 and Messier’s in late summer, 1780. Pigott’s discovery was more or less ignored and recovered only by Bryn Jones in April 2002! (May the good Mr. Pigot know that he was remembered here and his reports placed first!!)
Messier 64, the Black Eye Galaxy. Credit: Miodrag Sekulic
So how did it get the name “Black Eye Galaxy”? We have Sir William Herschel to thank for that: “A very remarkable object, much elongated, about 12′ long, 4′ or 5′ broad, contains one lucid spot like a star with a small black arch under it, so that it gives one the idea of what is called a black eye, arising from fighting.” Of course, John Herschel perpetuated it when he wrote in his own notes:
“The dark semi-elliptic vacancy (indicated by an unshaded or bright portion in the figure,) which partially surrounds the condensed and bright nucleus of this nebula, is of course unnoticed by Messier. It was however seen by my Father, and shown by him to the late Sir Charles Blagden, who likened it to the appearance of a black eye, an odd, but not inapt comparison. The nucleus is somewhat elongated, and I have a strong suspicion that it may be a close double star, or extremely condensed double nebula.”
Locating Messier 64:
Locating M64 isn’t particularly easy. Begin by identifying bright orange Arcturus and the Coma Berenices star cluster (Melotte 111) about a hand span to the general west. As you relax and let your eyes dark adapt, you will see the three stars that comprise the constellation of Coma Berenices, but if you live under light polluted skies, you may need binoculars to find its faint stars. Once you have confirmed Alpha Comae, star hop approximately 4 degrees north/northwest to 35 Comae. You will find M64 around a degree to the northeast of star 35.
While Messier 64 is binocular possible, it will require very dark skies for average binoculars and will only show as a very small, oval contrast change. However, in telescopes as small as 102mm, its distinctive markings can be seen on dark nights with good clarity. Don’t fight over it… There’s plenty of dark dustlane in this Sleeping Beauty to go around!
The location of Messier 64 in the Coma Berenices constellation. Credit: IAU/Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)
And here are the quick facts on this Messier Object to help you get started:
Object Name: Messier 64 Alternative Designations: M64, NGC 4826, The Black Eye Galaxy, Sleeping Beauty Galaxy, Evil Eye Galaxy Object Type: Type Sb Spiral Galaxy Constellation: Coma Berenices Right Ascension: 12 : 56.7 (h:m) Declination: +21 : 41 (deg:m) Distance: 19000 (kly) Visual Brightness: 8.5 (mag) Apparent Dimension: 9.3×5.4 (arc min)
Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at that buzzing nest of stars – the Beehive Cluster!
During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.
One of these is the Beehive Cluster (aka. Messier 44, or Praesepe), an open star cluster located in the the Cancer constellation. In addition to containing a larger population of stars than most clusters in its vicinity, it is also one of the nearest open clusters to the Solar System – at a distance of 577 light years (177 parsecs). As such, astronomers have been aware of it since Classical Antiquity.
Description:
According to ancient lore, this group of stars (often called the Praesepe) foretold a coming storm if it was not visible in otherwise clear skies. Of course, this came from a time when combating light pollution meant asking your neighbors to dim their candles. But, once you learn where it’s at, it can be spotted unaided even from suburban settings. Hipparchus called it the “Little Cloud,” but not until the early 1600s was its stellar nature revealed.
Close up of the Praesepe (Messier 44) open star cluster. Credit: Wikisky
Believed to be about 550 light-years away, this awesome cluster consists of hundreds of members – with at least four orange giants and five white dwarfs. M44’s age is similar to that of the Pleiades, and it is believed that both clusters have a common origin. Although you won’t see any nebulosity in the Beehive, even the very smallest of binoculars will reveal a swarm of bright stars and large telescopes can resolve down to 350 faint stars.
Messier 44 is the nearest open cluster of its type to our Solar System, and it contains a larger star population than most other nearby clusters. Under dark skies the Beehive Cluster looks like a nebulous object to the unaided eye; thus it has been known since ancient times. The classical astronomer Ptolemy called it “the nebulous mass in the heart of Cancer,” and it was among the first objects that Galileo studied with his telescope.
The cluster’s age and proper motion coincide with those of the Hyades stellar association, suggesting that both share a similar origin. Both clusters also contain red giants and white dwarfs, which represent later stages of stellar evolution, along with main sequence stars of spectral classes A, F, G, K, and M. So far, eleven white dwarfs have been identified, representing the final evolutionary phase of the cluster’s most massive stars, which originally belonged to spectral type B. Brown dwarfs, however, are extremely rare in this cluster, probably because they have been lost by tidal stripping from the halo.
Messier 44 is home to 5 red giant stars and a handful of white dwarf stars. But, M44 also contains one peculiar blue star. Among its members, there is the eclipsing binary TX Cancri, the metal line star Epsilon Cancri, and several Delta Scuti variables of magnitudes 7-8, in an early post-main-sequence state. And in all those stars, there’s a lot of other peculiarities to be found!
Atlas Image of the Beehive Cluster obtained as part of the Two Micron All Sky Survey (2MASS). Credit: UMass/IPAC (Caltech)/NASA/NSF
As Sergei M. Andrievsky indicated in a 1998 study:
“We present the results of a spectroscopic study of four blue stragglers from old galactic open cluster NGC 2632 (Praesepe). The LTE analysis based on Kurucz’s atmosphere models and synthetic spectra technique has shown that three stars, including the hottest star of the cluster HD73666, possess an uniform chemical composition: they show a solar-like abundance (or slight overabundance) of iron and an apparent deficiency of oxygen and silicon. Two stars exhibit a remarkable barium overabundance. The chemical composition of their atmospheres is typical for Am stars. One star of our sample does not share such uniform elemental distribution, being generally deficient in metals.”
But is there more hiding in there? Perhaps the kind of stuff that could eventually make planets? According to a 2009 study done by A. Gaspar (et al), this was certainly thought to the be the case:
“Mid-IR excesses indicating debris disks are found for one early-type and for three solar-type stars. The incidence of excesses is in agreement with the decay trend of debris disks as a function of age observed for other cluster and field stars. We show that solar-type stars lose their debris disk 24 um excesses on a shorter timescale than early-type stars. Simplistic Monte Carlo models suggest that, during the first Gyr of their evolution, up to 15%-30% of solar-type stars might undergo an orbital realignment of giant planets such as the one thought to have led to the Late Heavy Bombardment, if the length of the bombardment episode is similar to the one thought to have happened in our solar system.”
In September of 2012, two planets were confirmed to be orbiting around two separate stars in the Beehive Cluster. The finding was significant since the stars were similar to Earth’s Sun, and this was the first instance where exoplanets were found orbiting a Sun-like star within a stellar cluster. These planets were designated as Pr0201b and Pr0211b, both of which are “Hot Jupiters” (i.e. gas giants that orbit close to their stars). In 2016, additional observations showed that the Pr0211 system actually has two planets, the second one being Pr0211-c.
History of Observation:
This beautiful, nearby star cluster has been known since ancient times and played wonderful roles in mythology. Aratos mentioned this object as “Little Mist” as far back as 260 BC, and Hipparchus included this object in his star catalog and called it “Little Cloud” or “Cloudy Star” in 130 BC. Ptolemy mentions it as one of seven “nebulae” he noted in his Almagest, and describes it as “The Nebulous Mass in the Breast (of Cancer)”.
According to Burnham, it appeared on Johann Bayer’s chart (about 1600 AD) as “Nubilum” (“Cloudy” Object). It was even resolved by Galileo in 1609 who said: “The nebula called Praesepe contains not one star only but a mass of more than 40 small stars. We have noted 36 besides the Aselli (Gamma and Delta Cancri).”
Messier 44 was partly resolved by Orion nebula’s discoverer, Peiresc, in 1611, who said, “Nebula was seen in the vicinity of Jupiter to the east. in which more than 15 stars have been counted.” and added to Hevelius’ catalog as number 291. De Cheseaux charted it as his number 11 and Bode as his number 20. Small wonder Messier felt the need to add his own numbers to it as well when he recorded:
“At simple view [with the naked eye], one sees in Cancer a considerable nebulosity: this is nothing but a cluster of many stars which one distinguishes very well with the help of telescopes, and these stars are mixed up at simple view [to the unaided eye] because of their great proximity. The position in right ascension of one of the stars, which Flamsteed has designated with the letter c, reduced to March 4, 1769, should be 126d 50′ 30″, for its right ascension, and 20d 31′ 38″ for its northern declination. This position is deduced from that which Flamsteed has given in his catalog.”
Image of M44 Beehive cluster taken by the author, Miguel Garcia. Credit: Intihuatana (Miguel Garcia)
While Sir William Herschel would ignore it and Caroline Herschel would only write that she “observed it”, John Herschel would go on to give it an NGC designation and Admiral Smyth would sing its poetic praises. Is it possible that watching this star cluster could help fortell the weather? If you believe the words of Aratos, it just might.
“Watch, too, the Manger. Like a faint mist in the North it plays the guide beneath Cancer. Around it are borne two faintly gleaming stars, not far apart nor very near but distant to the view a cubit.s length, one on the North, while the other looks towards the South. They are called the Asses [in the constellation Cancer], and between them is the Manger. On a sudden, when all the sky is clear, the Manger wholly disappears, while the stars that go on either side seem nearer drawn to one another: not slight then is the storm with which the fields are deluged. If the Manger darken and both stars remain unaltered, they herald rain. But if the Ass to the North of the Manger shine feebly through a faint mist, while the Southern Ass is gleaming bright, expect wind from the South: but if in turn the Southern Ass is cloudy and the Northern bright, watch for the North wind.”
And watch for a swarm of incredible starlight!
Locating Messier 44:
Messier 44 is so bright that it easily shows to the unaided eye as a nebulous patch just above the conjunction of the faint, upside down “Y” asterism of the Cancer constellation. However, not everyone lives where dark skies are a rule – so try using both Pollux and Procyon to form the base of an imaginary triangle. Now aim your binoculars or finderscope near the point of the apex to discover M44 – the Beehive.
The location of Messier 44 in the Cancer constellation. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)
Since Messier 44 is about a degree and a half in diameter, it will require that you use your lowest magnification eyepiece in a telescope, and it is very well suited to binoculars of all sizes. Because its major stars are also quite bright, it stands up to urban sky and moonlight conditions, but many more stars are revealed with higher magnification and darker skies. Because M44 is very near the ecliptic plane, you’ll often find a planet or the Moon mixing it up with the stars!
Object Name: Messier 44 Alternative Designations: M44, NGC 2632, Beehive Cluster, The Praesepe, The Manger Object Type: Open Galactic Star Cluster Constellation: Cancer Right Ascension: 08 : 40.1 (h:m) Declination: +19 : 59 (deg:m) Distance: .577 (kly) Visual Brightness: 3.7 (mag) Apparent Dimension: 95.0 (arc min)
The De Mairan's Nebula (aka. Messier 43) and the Orion Nebula. Credit: Wikisky
Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at Orion’s Nebula’s “little brother”, the De Marian’s Nebula!
During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.
One of these if the diffuse nebula known as the De Marian’s Nebula (aka. Messier 43). Located in the direction of the Orion constellation (in close proximity to the Orion Nebula), this nebula lies at a distance of 1,600 light years from Earth. Together with the Orion Nebula, it is part of one of the most active star-forming regions visible in the night sky.
Description:
The diffuse nebula M43 surrounds the variable star N U Orionis (HD 37061) – a rather cool, young star cooking in a rich HII region. But is the light that’s reaching us actually coming through a tunnel in this dusty cloud? As Karl Wurm and Mario Perinotto explained in a 1970 study:
“Most of the areas with identical monochromatic features show a high deficiency of cluster stars correlated with a low surface brightnesss and a reduced gas density. This is explained by an opaqueness of the emission strata in the direction in the line of sight and a position of the same nearer to the observer than the extension of the cluster. There appear surface structures at large distances from the Trapezium which show a correlation between the intensity of scattered star light and the intensity of the emission of the higher ions ([Oiii], [Neiii]). This observation is considered as a proof that canals through the nebular cloud complex allow in some directions the exciting radiation to reach large distances from the star without having suffered an appreciable absorption or scattering.”
De Mairan’s Nebula, M43, NGC 1982. Credit: NASA/ESA/M. Robberto (Space Telescope Science Institute/ESA)/Hubble Space Telescope Orion Treasury Project Team
However, N U is far from being alone…. The whole complex is littered with stars being born! As Bo Reipurth (et al), stated in a 1999 study:
“The OMC-2/3 molecular clouds contain one of the highest concentrations of protostars known in nearby molecular clouds. We have observed an area of about 6 × 15 (0.8 pc × 2 pc) covering the OMC-2/3 region with the Very Large Array in the D configuration at 3.6 cm, matching well the area of a recent 1300 m survey. We detected 14 sources, of which it is highly probable that 11 sources are either protostars or very young stars. This testifies to the star-forming activity and extreme youth of the OMC-2/3 region. The 3.6 cm flux is free-free emission probably due to shocks in outflowing material. Three of the sources are extended even with the relatively low resolution of the present observations, and two of these may be collimated radio jets. The large fraction of submillimeter continuum sources that have a radio continuum counterpart is evidence that outflow is already common at the very earliest evolutionary stages. No relation is found between the radio continuum flux and the 1300 m flux of the associated submillimeter dust clumps.”
History of Observation:
In 1731, Jean-Jacques Dortous de Mairan was the first to notice this independent portion of the Orion nebula, stating:
“Finally I will add that close to the luminous space in Orion [M42], one sees the star d of Huygens [NU Orionis] currently (1731) surrounded by a brilliance very similar to that which produces, as I believe, the atmosphere of our Sun, if it were dense enough and extensive enough to be visible in Telescopes at a similar distance. See it in the form and the situation [given by] D, according to what was determined with the Reticule.”
On March 4, 1771, Charles Messier would also come to the same conclusion as he states in his observing notes:
“The star which is above, and has little distance from that nebula, and of which is spoken in the Traite de l’Aurore boreale [Treat of the Northern Light] by M. de Mairan is surrounded, and equally by a very thin light; the star doesn’t have the same brilliance as the four of the great nebula: its light is pale, and it appears covered by fog. I determined its position; its right ascension was 81d 3′ 0″, and its declination 5d 26′ 37″ south.”
Close-up view of the Orion Nebula’s little brother, Messier 43, taken by NASA/ESA Hubble Space Telescope. Credit: ESA/Hubble & NASA
While Sir William Herschel was very careful not to assign his own catalog numbers to Messier Objects, he, too, was fascinated by the M43 region. In his personal notes he writes:
“In the year 1774, the 4th of March, I observed the nebulous star, which is the 43d of the Connoissance des Temps and is not many minutes north of the great nebula; but at the same time I also took notice of two similar, but much smaller nebulous stars; one on each side of the large one, and at nearly equal distance from it. Fig. 37 is a copy of the drawing which was made at the time of observation.
“In 1783, I reexamined the nebulous star, and found it to be faintly surrounded with a circular glory of whitish nebulosity, faintly joined to the great nebula. About the latter end of the same year I remarked that it was not equally surrounded, but most nebulous toward the south.
“In 1784, I began to entertain an opinion that the star was not connected with the nebulosity of the great nebula in Orion, but was one of those which are scattered over that part of the heavens.
“In 1801, 1806, and 1810 this opinion was fully confirmed, by the gradual change which happened in the great nebula, to which the nebulosity surrounding this star belongs. For the intensity of the light about the nebulous star had by this time been considerably reduced, by attenuation or dissipation of nebulous matter; and it seemed now to be pretty evident that the star is far behind the nebulous matter, and that consequently its light in passing through it is scattered and deflected, so as to produce the appearance of a nebulous star. A similar phenomenon may be seen whenever a planet or a star of the 1st or 2nd magnitude happens to be involved in haziness; for a diffused circular light will then be seen, to which, but in a much inferior degree, that which surrounds this nebulous star bears a great resemblance.
“When I reviewed this interesting object in December 1810, I directed my attention particularly to the two small nebulous stars, by sides of the large one, and found that they were perfectly free from every nebulous appearance; which confirmed not only my former surmise of the great attenuation of the nebulosity, but also proved that their former nebulous appearance had been entirely the effect of the passage of their feeble light through the nebulous matter spread out before them.
The 19th of January 1811, I had another critical examination of the same object in a very clear view through the 40-feet telescope; but notwithstanding the superior light of this instrument, I could not perceive any remains of nebulosity about the two small stars, which were perfectly clear, and in the same situation, where about thirty-seven years before I had seen them involved in nebulosity.”
May this wonderful region entertain your brain for as many years as it did Bill Herschel!
The location of Messier 43 in the constellation of Orion. Credit: IAU/Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)
Locating Messier 43:
Locating M43 is as easy as locating… well… M42! This small star cluster accompanied by an emission/reflection nebula just to the north of the Orion Nebula’s “Trapezium” region is often mistake for part of the great nebula itself. However, if you look closely, you’ll see the two are separated by a dark dust lane.
Begin by locating the asterism of three stars known as Orion’s Belt. If you cover it with your fist held at arm’s length in a “thumb’s down” gesture with your left hand, the tip of your thumb will just about mark the correct spot in the sky. From a dark location when no Moon is present, you can easily see the haze of the Orion nebula surrounding the stars in the “sword” asterism. While it is easily seen in binoculars on a dark night, it will fade significantly under light pollution or moonlight.
And here are the quick facts on Messier 43 to help you get started:
Object Name: Messier 43 Alternative Designations: M43, NGC 1982, De Mairan’s Nebula, Companion of the Orion Nebula Object Type: Emission/Reflection Nebula and Open Cluster Constellation: Orion Right Ascension: 05 : 35.6 (h:m) Declination: -05 : 16 (deg:m) Distance: 1.3 (kly) Visual Brightness: 9.0 (mag) Apparent Dimension: 20×15 (arc min)
Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the open galactic star cluster known as Messier 39. Enjoy!
During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.
One of these objects is known as Messier 39, an open star cluster located in the direction of the Cygnus constellation. Because of its proximity to Deneb and its size – it is actually larger in the night sky than a full Moon – it is easily observed using binoculars and small, low magnification telescopes.
Description:
Positioned only about 800 light years away from our solar system, this 300 million year old group of about 30 stars may look like they are spread fairly far apart in the sky. But as clusters go, they are close, really close! This group is gathered in space in only a 7 light year neighborhood! All of its stars are main sequence and the very brightest of them are just about to evolve into the red giant star phase.
In a study done by Jean Claude Mermilliod (et al), they conducted a long-term monitoring of solar-type dwarfs with CORAVEL – a study which took 19 years. While most individual radial velocities were never published – apart from a small number of spectroscopic binaries – the stars themselves and their properties were well documented in the works of B. Uyaniker and T. L. Landecker of the National Research Council, Herzberg Institute of Astrophysics.
Low-magnification image of Messier 39. Credit: Christian van Endern
“We describe a Faraday rotation structure in the interstellar medium detected through polarimetric imaging at 1420 MHz from the Canadian Galactic Plane Survey (CGPS). The structure, at l = 918,b = -25, has an extent of ~2°, within which polarization angle varies smoothly over a range of ~100°. Polarized intensity also varies smoothly, showing a central peak within an outer shell. This region is in sharp contrast to its surroundings, where low-level chaotic polarization structure occurs on arcminute scales. The Faraday rotation structure has no counterpart in radio total intensity and is unrelated to known objects along the line of sight, which include a Lynds Bright Nebula, LBN 416, and the star cluster M39 (NGC 7092). It is interpreted as a smooth enhancement of electron density. The absence of a counterpart, in either optical emission or total intensity, establishes a lower limit to its distance. An upper limit is determined by the strong beam depolarization in this direction. At a probable distance of 350 ± 50 pc, the size of the object is 10 pc, the enhancement of electron density is 1.7 cm-3, and the mass of ionized gas is 23 M. It has a very smooth internal magnetic field of strength 3 UG, slightly enhanced above the ambient field. G91.8-2.5 is the second such object to be discovered in the CGPS, and it seems likely that such structures are common in the magneto-ionic medium.”
So where do these gases come from? Perhaps they are there all along. As Yu N. Efremov and T.G. Sitnik wrote in their 1988 study:
“It is found that about 90% of young clusters o-b2 and OB-associations situated within 3 kpc from the Sun are united into complexes with diameters from 150 to 700 pc. Almost all complexes contain giant molecular clouds with masses. A number of complexes (mostly large ones)-are connected with giant H I clouds; a few of small complexes are situated in the H I-caverns. Older (>b2) cluster avoid the regions occupied by young star groups. Complexes often have an hierarchic structure; some neighbouring complexes may be united into supercomplexes with diameters about 1.5 kpc.”
Does this mean it’s possible that M39 could be more than one cluster combined? As H. Schneider wrote in his 1987 study:
“Early-type stars up to 12.0 mag and spectral type F2 in two young northern clusters were investigated by means of Stromgren and H-beta photometry. The distance and reddening of the clusters were estimated, and the membership of the stars discussed. In the case of NGC 7039 a distance of 675 pc and a color excess of E(b-y) = 0.056 were found; the respective values for NGC 7063 were 635 pc and E(b-y) = 0.062. The reality of NGC 7039 is somewhat puzzling: it seems that there exists a loose star aggregate called NGC 7039, containing about six to nine stars, and in the background another cluster at a distance of about 1500 pc. Besides this, variable reddening across the cluster area is probable.”
Atlas Image mosaic of Messier 39, obtained as part of the Two Micron All Sky Survey (2MASS). Credit: NASA/NSF/IPAC/Caltech/Univ. of Mass.
History of Observation:
While it is possible this bright star cluster was remarked upon by Aristotle as a cometary appearing object about 325 BC, and it is also possible that it may have been discovered by Le Gentil in 1750, the fact remains M39 is most frequently attributed to be an original discovery of Charles Messier. As he recorded in his notes:
“In the night of October 24 to 25, 1764, I observed a cluster of stars near the tail of Cygnus: One distinguishes them with an ordinary (nonachromatic) refractor of 3 and a half feet; they don’t contain any nebulosity; its extension can occupy a degree of arc. I have compared it with the star Alpha Cygni, and I have found its position in right ascension of 320d 57′ 10″, and its declination of 47d 25′ 0″ north.”
Because Sir William Herschel did not publish his findings on Messier’s works, very few have read his observations of the object -“Consists of such large and straggling stars that I could not tell where it began nor where it ended. It cannot be called a cluster.” However, it would later go on to receive a New General Catalog (NGC) designation by Sir John Herschel who would describe it as “A star of 7th mag [position taken], one of a large loose cluster of stars of 7th to 10th magnitude; very coarsely scattered, and filling many fields.”
Even as accomplished as historic observers were, they sometimes didn’t always do the right thing. In the case of Messier 39, it is so close to us that it appears large dimensionally in the sky – and therefore needs less magnification instead of more to be properly studied as a whole. However, don’t always put away the magnfication, because as Admiral Smyth reports:
“A loose cluster, or rather splashy galaxy field of stars, in a very rich visinity between the Swan’s tail and the Lizard, due south of Beta Cephei, and east-north-east of Deneb [Alpha Cygni]. This was picked up by Messier in 1764, with his 3 1/2 foot telescope, and registered as being a degree in diameter. Among them there are several pairs, of which a couple were slightly estimated; the first being the brightest star (7m) and its comes, and the second a pretty pair of 10th-magnitudes.”
The location of Messier 39 in the Cygnus constellation. Credit: IAU/Sky & Telescope magazine/Roger Sinnott & Rick Fienberg)
Locating Messier 39:
This coarse open star cluster is easily found in small optics. Start first by identifying the very large constellation of Cygnus and pinpointing its brightest, northernmost star. Aim you binoculars there. You’ll find M39 about 9 degrees east and a bit north of Deneb (Alpha Cygni). If at first you don’t succeed, try looking at Deneb from a dark sky location and see if you can spot a small, hazy patch about a fist width away to the east. There’s your star cluster!
It will also show easily in the telescope finderscope as a hazy patch and even begin resolution with larger aperture finders. M39 is very well suited to light polluted skies and moonlit observing and will even hold up well to less than ideal sky conditions. Small instruments will easily see a bright handful of stars while larger telescopes will resolve many more faint members and pairs. Because of its large apparent size, you’ll enjoy viewing M39 far more if you use the least amount of magnification possible.
Enjoy this star-studded cluster and the great Milky Way field that frames it!
And here are the quick facts on this Messier Object to help get you started:
Object Name: Messier 39 Alternative Designations: M39, NGC 7092 Object Type: Galactic Open Star Cluster Constellation: Cygnus Right Ascension: 21 : 32.2 (h:m) Declination: +48 : 26 (deg:m) Distance: 0.825 (kly) Visual Brightness: 4.6 (mag) Apparent Dimension: 32.0 (arc min)
The Messier 30 globular cluster, in proximigy to other deep sky objects in the direction of the Capricornus constellation. Credit: Wikisky
Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the globular cluster known as Messier 30. Enjoy!
During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list (known as the Messier Catalog) would come to include 100 of the most fabulous objects in the night sky.
One of these objects is Messier 30, a globular cluster located in the southern constellation of Capricornus. Owing to its retrograde orbit through the inner galactic halo, it is believed that this cluster was acquired from a satellite galaxy in the past. Though it is invisible to the naked eye, this cluster can be viewed using little more than binoculars, and is most visible during the summer months.
Description:
Messier measures about 93 light years across and lies at a distance of about 26,000 light years from Earth, and approaching us at a speed of about 182 kilometers per second. While it looks harmless enough, its tidal influence covers an enormous 139 light years – far greater than its apparent size.
Half of its mass is so concentrated that literally thousands of stars could be compressed in an area that spans no further than the distance between our solar system and Sirius! However, inside this density only 12 variable stars have been found and very little evidence of any stellar collisions, although a dwarf nova has been recorded!
So what’s so special about this little globular? Try a collapsed core – and one that’s even been resolved by Earth-bound telescopes. According to Bruce Jones Sams III, an astrophysicists at Harvard University:
“The globular cluster NGC 7099 is a prototypical collapsed core cluster. Through a series of instrumental, observational, and theoretical observations, I have resolved its core structure using a ground based telescope. The core has a radius of 2.15 arcsec when imaged with a V band spatial resolution of 0.35 arcsec. Initial attempts at speckle imaging produced images of inadequate signal to noise and resolution. To explain these results, a new, fully general signal-to-noise model has been developed. It properly accounts for all sources of noise in a speckle observation, including aliasing of high spatial frequencies by inadequate sampling of the image plane. The model, called Full Speckle Noise (FSN), can be used to predict the outcome of any speckle imaging experiment. A new high resolution imaging technique called ACT (Atmospheric Correlation with a Template) was developed to create sharper astronomical images. ACT compensates for image motion due to atmospheric turbulence.”
Photography is an important tool for astronomers to work with – both land and space-based. By combining results, we can learn far more than just from the results of one telescope observation alone. As Justin H. Howell wrote in a 1999 study:
“It has long been known that the post-core-collapse globular cluster M30 (NGC 7099) has a bluer-inward color gradient, and recent work suggests that the central deficiency of bright red giant stars does not fully account for this gradient. This study uses Hubble Space Telescope Wide Field Planetary Camera 2 images in the F439W and F555W bands, along with ground-based CCD images with a wider field of view for normalization of the noncluster background contribution. The quoted uncertainty accounts for Poisson fluctuations in the small number of bright evolved stars that dominate the cluster light. We explore various algorithms for artificially redistributing the light of bright red giants and horizontal-branch stars uniformly across the cluster. The traditional method of redistribution in proportion to the cluster brightness profile is shown to be inaccurate. There is no significant residual color gradient in M30 after proper uniform redistribution of all bright evolved stars; thus, the color gradient in M30’s central region appears to be caused entirely by post-main-sequence stars.”
Image of Messier 30 (M 30, NGC 7099) was taken by Hubble’s Advanced Camera for Surveys (ACS). Credit: NASA/ESA
“We report the detection of six discrete, low-luminosity X-ray sources, located within 12” of the center of the collapsed-core globular cluster M30 (NGC 7099), and a total of 13 sources within the half-mass radius, from a 50 ks Chandra ACIS-S exposure. Three sources lie within the very small upper limit of 1.9” on the core radius. The brightest of the three core sources has a blackbody-like soft X-ray spectrum, which is consistent with it being a quiescent low-mass X-ray binary (qLMXB). We have identified optical counterparts to four of the six central sources and a number of the outlying sources, using deep Hubble Space Telescope and ground-based imaging. While the two proposed counterparts that lie within the core may represent chance superpositions, the two identified central sources that lie outside of the core have X-ray and optical properties consistent with being cataclysmic variables (CVs). Two additional sources outside of the core have possible active binary counterparts.”
History of Observation:
When Charles Messier first encountered this globular cluster in 1764, he was unable to resolve individual stars, and mistakenly believed it to be a nebula. As he wrote in his notes at the time:
“In the night of August 3 to 4, 1764, I have discovered a nebula below the great tail of Capricornus, and very near the star of sixth magnitude, the 41st of that constellation, according to Flamsteed: one sees that nebula with difficulty in an ordinary [non-achromatic] refractor of 3 feet; it is round, and I have not seen any star: having examined it with a good Gregorian telescope which magnifies 104 times, it could have a diameter of 2 minutes of arc. I have compared the center with the star Zeta Capricorni, and I have determined its position in right ascension as 321d 46′ 18″, and its declination as 24d 19′ 4″ south. This nebula is marked in the chart of the famous Comet of Halley which I observed at its return in 1759.”
Image of the core region of Messier 30 by the Hubble Space Telescope. Credit: NASA
However, we cannot fault Messier, for his job was to hunt comets and we thank him for logging this object for further study. Perhaps the first clue to M30’s underlying potential came from Sir William Herschel, who often studied Messier’s objects, but did not report his findings formally. In his personal notes he wrote:
“A brilliant cluster, the stars of which are gradually more compressed in the middle. It is insulated, that is, none of the stars in the neighborhood are likely to be connected with it. Its diameter is from 2’40” to 3’30”. The figure is irregularly round. The stars about the centre are so much compressed as to appear to run together. Towards the north, are two rows of bright stars 4 or 5 in a line. In this accumulation of stars, we plainly see the exertion of a central clustering power, which may reside in a central mass, or, what is more probable, in the compound energy of the stars about the centre. The lines of bright stars, although by a drawing made at the time of observation, one of them seems to pass through the cluster, are probably not connected with it.”
So, as telescopes progressed and resolution improved, so did our way of thinking about what we were seeing… By Admiral Smyth’s time, things had improved even more and so had the art of understanding more:
“A fine pale white cluster, under the creature’s caudal fin, and about 20 deg west-north-west of Fomalhaut, where it precedes 41 Capricorni, a star of 5th magnitude, within a degree. This object is bright, and from the straggling streams of stars on its northern verge, has an elliptical aspect, with a central blaze; and there are but few other stars, or outliers, in the field.
“When Messier discovered this, in 1764, he remarked that it was easily seen with a 3 1/2-foot telescope, that it was a nebula, unaccompanied by any star, and that its form was circular. But in 1783 it was attacked by WH [William Herschel] with both his 20-foot Newtonians, and forthwith resolved into a brilliant cluster, with two rows pf stars, four or five in a line, which probably belong to it; and therefore he deemed it insulated. Independently of this opinion, it is situated in a blankish space, one of those chasmata which Lalande termed d’espaces vuides, wherein he could not perceive a star of the 9th magnitude in the achromatic telescope of sixty-seven millimetres aperture. By a modification of his very ingenious gauging process, Sir William considered the profundity of this cluster to be of the 344th order.
“Here are materials for thinking! What an immensity of space is indicated! Can such an arrangement be intended, as a bungling spouter of the hour insists, for a mere appendage to the speck of a world on which we dwell, to soften the darkness of its petty midnight? This is impeaching the intelligence of Infinite Wisdom and Power, in adapting such grand means to so disproportionate an end. No imagination can fill up the picture of which the visual organs afford the dim outline; and he who confidently probes the Eternal Design cannot be many removes from lunacy. It was such a consideration that made the inspired writer claim, “How unsearchable are His operations, and His ways past finding out!”
Throughout all historic observing notes, you’ll find notations like “remarkable” and even Dreyer’s famous exclamation points. Even though M30 may not be the easiest to find, nor the brightest of the Messier objects, it is still quite worthy of your time and attention!
The location of Messier 30, in the direction of the Scorpius constellation. Credit: IAU/Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)
Locating Messier 30:
Finding M30 is not an easy task, unless you’re using a GoTo telescope. In any other case, it’s a starhop process, which must begin with identifying the the big grin-shape of the constellation of Capricornus. Once you’ve separated out this constellation, you’ll begin to notice that many of its primary asterism stars are paired – which is a good thing! The northeastern most pair are Gamma and Delta, which is where binocular-users should start.
As you move slowly south and slightly west, you’ll encounter your next wide pair – Chi and Epsilon. The next southwestern set is 36 Cap and Zeta. Now, from here you have two options! You can find Messier 30 a little more than a finger width east(ish) of Zeta (about half a binocular field)… or, you can return to Epsilon and look about one binocular field south (about 3 degrees) for star 41 which will appear just east of Messier 30 in the same field of view.
For the finderscope, star 41 is a critical giveaway to the globular cluster’s position! It won’t be visible to the unaided eye, but even a little magnification will reveal its presence. Using binoculars or a very small telescope, Messier 30 will appear as only a small, faded gray ball of light with a small star beside it. However, with telescope apertures as small as 4″ you’ll begin some resolution on this overlooked globular cluster and larger apertures will resolve it nicely.
And here are the quick facts on Messier 30 to help you get started:
Object Name: Messier 30 Alternative Designations: M30, NGC 7099 Object Type: Class V Globular Cluster Constellation: Capricornus Right Ascension: 21 : 40.4 (h:m) Declination: -23 : 11 (deg:m Distance: 26.1 (kly) Visual Brightness: 7.2 (mag) Apparent Dimension: 12.0 (arc min)
Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the open star cluster known as Messier 29. Enjoy!
During the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list would come to include 100 of the most fabulous objects in the night sky.
One of these objects is Messier 29, an open star cluster located in the northern skies in the direction of the Cygnus constellation. Situated in a highly crowded area of the Milky Way Galaxy, about 4,000 light-years from Earth, this star cluster is slowly moving towards us. Though somewhat isolated in the night sky, it can be easily spotted using binoculars and small telescopes.
Description:
While Messier Object 29 might appear a little bit boring compared to some of its more splashy catalog companions, it really isn’t. This little group of stars is part of the Cygnus OB1 association which just happens to be heading towards us at a speed of 28 kilometers per second (17.4 mps) . If it weren’t obscured by Milky Way dust, the light of its stars would be 1000 times brighter!
Messier 29 and Gamma Cygni (Sadr). Credit: Wikisky
All in all, M29 has around 50 member stars, but this 10 million year old star cluster still has some surprises. The five brightest stars you see are are all giant stars of spectral class B0, and if we were to put one next to our own Sol, it would shine 160,000 times brighter. Image just how “lit up” any planet might be that would reside inside that 11 light year expanse!
Astronomers were curious about Messier 29, too, so they went in search of binary stars. As C. Boeche (et al) wrote in a 2003 study:
“Between 1996 and 2003 we obtained 226 high resolution spectra of 16 stars in the field of the young open cluster NGC 6913, to constrain its main properties and study its internal kinematics. Twelve of the program stars turned out to be members, one of them probably unbound. Nine are binaries (one eclipsing and another double lined) and for seven of them the observations allowed us to derive the orbital elements. All but two of the nine discovered binaries are cluster members. In spite of the young age (a few Myr), the cluster already shows signs that could be interpreted as evidence of dynamical relaxatin and mass segregation.
“However, they may be also the result of an unconventional formation scenario. The dynamical (virial) mass as estimated from the radial velocity dispersion is larger than the cluster luminous mass, which may be explained by a combination of the optically thick interstellar cloud that occults part of the cluster, the unbound state or undetected very wide binary orbit of some of the members that inflate the velocity dispersion and a high inclination for the axis of possible cluster angular momentum. All the discovered binaries are hard enough to survive average close encounters within the cluster and do not yet show signs of relaxation of the orbital elements to values typical of field binaries.”
So why is finding binary stars important? Evolution is the solution, the hunt for Be stars. As S.L. Malchenko of the Crimean Astrophysical Observatory wrote in a 2008 study on Be stars:
“The phenomenon of Be stars has been known for over a century. The fact that at least 20% of B stars have an emission spectrum supports that the definition that this phenomenon is not special but it is rather typical from a large group of objects at a certain stage of evolution. The vagueness of the concept of the Be phenomenon suggests that this definition encompasses a broad group of objects near the main sequence that includes binary systems with different rate of mass exchange. This young open cluster in the Cyg OB1 association, is also know as M29, contains a large number of luminous stars with spectral types around B0. An extreme variation of extinction is found across the young open cluster NGC 6913, extinction in the cluster center is relatively homogeneous, but very large. We observed 10 spectra for 7 B stars and one known Be star in the blue region.”
Close-up of the core region of Messier 29. Credit: Adam Block/Mount Lemmon SkyCenter/University of Arizona
Although you won’t be able to detect it visually, there is also some nebulosity associated with M29, which is another important clue to this star cluster’s evolution. As B. Bhavya of Cochin University of Science and Technology wrote in a 2008 study:
“The Cygnus region is a region of recent star formation activity in the Milky Way and is rich in massive early type stars concentrated in OB associations. The presence of nebulosity and massive stars indicate that the stars have been forming till very recently and the young clusters found here are the result of the recent star formation event. Though the above fact is known, what is not known is that when this star formation process started and how it proceeded in the region. Though one assumes that all the stars in a cluster have the same age, this assumption is not valid when the candidate cluster is very young. In the case of young clusters, there is a chance for a spread in the age of the stars, depending on the duration of star formation. An estimation of this formation time-scale in the clusters formed in a star forming complex, will indicate the duration of star formation and its direction of propagation within the complex. In principle, duration of star formation is defined as the difference between the ages of the oldest and the youngest star formed in the cluster. In practice, the age of the oldest star is assumed as the age of that star which is about to turn-off from the main-sequence (MS) (turn-off age) and the age of the youngest star is the age of the youngest pre-MS star (turn-on age). The turn-off age of many clusters are known, but the turn-on age is not known for most of the clusters.”
History of Observation:
This cool little star cluster was an original discovery of Charles Messier, who first observed it in 1764. As he wrote of the object in his notes at the time:
“In the night of July 29 to 30, 1764, I have discovered a cluster of six or seven very small stars which are below Gamma Cygni, and which one sees with an ordinary refractor of 3 feet and a half in the form of a nebula. I have compared this cluster with the star Gamma, and I have determined its position in right ascension as 303d 54′ 29″, and its declination of 37d 11′ 57″ north.”
Gammy Cygni (the brightest object in the center) and neighboring regions. Credit: Wikipedia Commons/Erik Larsen
In the case of this cluster, it was independently recovered again by Caroline Herschel, who wrote: “About 1 deg under Gamma Cygni; in my telescope 5 small stars thus. My Brother looked at them with the 7 ft and counted 12. It is not in Mess. catalogue.”
William would also return to the cluster as well with his own observations: “Is not sufficiently marked in the heavens to deserve notice, as 7 or 8 small stars together are so frequent about this part of the heavens that one might find them by hundreds.”
So why the confusion? In this circumstance, perhaps Messier was a bit distracted, for it would appear that his logged coordinates were somewhat amiss. Leave it to Admiral Symth to set the records straight:
“A neat but small cluster of stars at the root of the Swan’s neck, and in the preceding branch of the Milky Way, not quite 2deg south of Gamma; and preceding 40 Cygni, a star of the 6th magnitude, by one degree just on the parallel. In the sp [south preceding, SW] portion are the two stars here estimated as double, of which A is 8, yellow; B 11, dusky. Messier discovered this in 1764; and though his description of it is very fair, his declination is very much out: worked up for my epoch it would be north 37d 26′ 15″. But one is only surprised that, with his confined methods and means, so much was accomplished.”
Kudos to Mr. Messier for being able to distinguish a truly related group of stars in a field of so many! Take the time to enjoy this neat little grouping for yourself and remember – it’s heading our way.
Locating Messier 29:
Finding M29 in binoculars or a telescope is quite easy once you recognize the constellation of Cygnus. Its cross-shape is very distinctive and the marker star you will need to locate this open star cluster is Gamma – bright and centermost. For most average binoculars, you will only need to aim at Gamma and you will see Messier 29 as a tiny grouping of stars that resembles a small box.
The location of Messier 29, in the direction of the Cygus constellation. Credit: IAU and Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)
For a telescope, begin with your finderscope on Gamma, and look for your next starhop marker star about a finger width southwest. Once this star is near the center of your finderscope field, M29 will also be in a low magnification eyepiece field of view. Because it is a very widely spaced galactic open star cluster that only consists of a few stars, it makes an outstanding object that stands up to any type of sky conditions.
Except, of course, clouds! Messier 29 can easily be seen in light polluted areas and during a full Moon – making it a prize object for study for even the smallest of telescopes.
As always, here are the quick facts to help you get started:
Object Name: Messier 29 Alternative Designations: M29, NGC 6913 Object Type: Open Galactic Star Cluster Constellation: Cygnus Right Ascension: 20 : 23.9 (h:m) Declination: +38 : 32 (deg:m) Distance: 4.0 (kly) Visual Brightness: 7.1 (mag) Apparent Dimension: 7.0 (arc min)
Image of the Messier 27 planetary nebula, taken by NASA's Spitzer Space Telescope. Credit: NASA/JPL-Caltech/J. Hora (Harvard-Smithsonian CfA)
Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the famous and easily-spotted Dumbbell Nebula. Enjoy!
Back in the 18th century, famed French astronomer Charles Messier noted the presence of several “nebulous objects” in the night sky. Having originally mistaken them for comets, he began compiling a list of them so that others would not make the same mistake he did. In time, this list would come to include 100 of the most fabulous objects in the night sky.
Known today as the Messier Catalog, this work has come to be viewed as one of the most important milestones in the study of Deep Space Objects. One of these is the famed Dumbbell Nebula – also known as Messier 27, the Apple Core Nebula, and NGC 6853. Because it of its brightness, it is easily viewed with binoculars and amateur telescopes, and was the first planetary Nebula to be discovered by Charles Messier.
Description:
This bright planetary nebula is located in the direction of the Vulpecula constellation, at a distance of about 1,360 light years from Earth. Located within the equatorial plane, this nebula is essentially a dying star that has been ejecting a shell of hot gas into space for roughly 48,000 years.
Picture of M27 processed and combined using IRAF and MaxIm DL. Credit: Wikipedia Commons/Mohamad Abbas
The star responsible is an extremely hot blueish subdwarf star, which emits primarily highly energetic radiation in the non-visible part of the electromagnetic spectrum. This energy is absorbed by exciting the nebula’s gas, and then re-emitted by the nebula. Messier 27 particular green glow (hence the nickname “Apple Core Nebula”) is due to the presence of doubly-ionized oxygen in its center, which emits green light at 5007 Angstroms.
For many years I quested to understand the distant and mysterious M27, but no one could answer my questions. I researched it, and learned that it was made up of doubly ionized oxygen. I had hoped that perhaps there was a spectral reason to what I viewed year after year – but still no answer.
Like all amateurs, I became the victim of “aperture fever” and I continued to study M27 with a 12″ telescope, never realizing the answer was right there – I just hadn’t powered up enough. Several years later while studying at the Observatory, I was viewing through a friend’s identical 12″ telescope and, as chance would have it, he was using about twice the magnification that I normally used on the “Dumbbell.”
Imagine my total astonishment as I realized for the very first time that the faint central star had an even fainter companion that made it seem to wink! At smaller apertures or low power, this was not revealed. Still, the eye could “see” a movement within the nebula – the central, radiating star and its companion.
Image from a ground-based telescope at Westview Observatory in Cridersville, OH. Credit: Wikipedia Commons/Charlemagne920
“As the gas at the inner edge begins to ionize, the pressure throughout the nebula is equalized by a shock which moves outward through the neutral gas. Later, when about 1/10 of the nebular mass is ionized, a second shock is released from the ionized front, and this shock moves through the neutral shell reaching the outer edge. The density of the HI gas just behind the shock is quite large and the outward gas velocity increases within until it reaches a maximum of 40-80 km per second just behind the shock front. The projected appearance of the nebula during this stage has a double ring structure similar to many observed planetaries.”
But, movement or no movement, Messier 27 is known as one of the top “polluters” of the interstellar medium. As Joseph L. Hora ( et al.) of the Harvard-Smithsonian Center for Astrophysics said in his 2008 study “Planetary Nebulae: Exposing the Top Polluters of the ISM“:
“The high mass loss rates of stars in their asymptotic giant branch (AGB) stage of evolution is one of the most important pathways for mass return from stars to the ISM. In the planetary nebulae (PNe) phase, the ejected material is illuminated and can be altered by the UV radiation from the central star. PNe therefore play a significant role in the ISM recycling process and in changing the environment around them…
“A key link in the recycling of material to the Interstellar Medium (ISM) is the phase of stellar evolution from Asymptotic Giant Branch (AGB) to white dwarf star. When stars are on the AGB, they begin to lose mass at a prodigious rate. The stars on the AGB are relatively cool, and their atmospheres are a fertile environment for the formation of dust and molecules. The material can include molecular hydrogen (H2), silicates, and carbon-rich dust. The star is fouling its immediate neighborhood with these noxious emissions. The star is burning clean hydrogen fuel, but unlike a “green” hydrogen vehicle that outputs nothing except water, the star produces ejecta of various types, some of which have properties similar to that of soot from a gas-burning automobile. A significant fraction of the material returned to the ISM goes through the AGB – PNe pathway, making these stars one of the major sources of pollution of the ISM.
“However, these stars are not done with their stellar ejecta yet. Before the slow, massive AGB wind can escape, the star begins a rapid evolution where it contracts and its surface temperature increases. The star starts ejecting a less massive but high velocity wind that crashes into the existing circumstellar material, which can create a shock and a higher density shell. As the stellar temperature increases, the UV flux increases and it ionizes the gas surrounding the central star, and can excite emission from molecules, heat the dust, and even begin to break apart the molecules and dust grains. The objects are then visible as planetary nebulae, exposing their long history of spewing material into the ISM, and further processing the ejecta. There are even reports that the central stars of some PNe may be engaging in nucleosynthesis for purposes of self-enrichment, which can be traced by monitoring the elemental abundances in the nebulae. Clearly, we must assess and understand the processes going on in these objects in order to understand their impact on the ISM, and their influence on future generations of stars.”
Messier 27 and the Summer Triangle. Credit: Wikisky
History of Observation:
So, chances are on July 12th, 1764, when Charles Messier discovered this new and fascinating class of objects, he didn’t really have a clue as to how important his observation would be. From his notes of that night, he reports:
“I have worked on the research of the nebulae, and I have discovered one in the constellation Vulpecula, between the two forepaws, and very near the star of fifth magnitude, the fourteenth of that constellation, according to the catalog of Flamsteed: One sees it well in an ordinary refractor of three feet and a half. I have examined it with a Gregorian telescope which magnified 104 times: it appears in an oval shape; it doesn’t contain any star; its diameter is about 4 minutes of arc. I have compared that nebula with the neighboring star which I have mentioned above [14 Vul]; its right ascension has been concluded at 297d 21′ 41″, and its declination 22d 4′ 0″ north.”
Of course, Sir William Herschel’s own curiosity would get the better of him and although he would never publish his own findings on an object previously cataloged by Messier, he did keep his own private notes. Here is an excerpt from just one of his many observations:
“1782, Sept. 30. My sister discovered this nebula this evening in sweeping for comets; on comparing its place with Messier’s nebulae we find it is his 27. It is very curious with a compound piece; the shape of it though oval as M. [Messier] calls it, is rather divided in two; it is situated among a number of small [faint] stars, but with this compound piece no star is visible in it. I can only make it bear 278. It vanishes with higher powers on account of its feeble light. With 278 the division between the two patches is stronger, because the intermediate faint light vanishes more.”
So where did Messier 27 get its famous moniker? From Sir John Herschel, who wrote: “A most extraordinary object; very bright; an unresolved nebula, shaped something like an hour-glass, filled into an oval outline with a much less dense nebulosity. The central mass may be compared to a vertebra or a dumb-bell. The southern head is denser than the northern. One or two stars seen in it.”
It would be several years, and several more historical astronomers, before the true nature of Messier 27 would even be hinted at. At one level, they understood it to be a nebula – but it wasn’t until 1864 when William Huggins came along and began to decode the mystery:
“It is obvious that the nebulae 37 H IV (NGC 3242), Struve 6 (NGC 6572), 73 H IV (NGC 6826), 1 H IV (NGC 7009), 57 M, 18 H. IV (NGC 7662) and 27 M. can no longer be regarded as aggregations of suns after the order to which our own sun and the fixed stars belong. We have with these objects to do no longer with a special modification only of our own type of suns, but find ourselves in the presence of objects possessing a distinct and peculiar plan of structure. In place of an incandescent solid or liquid body transmitting light of all refrangibilities through an atmosphere which intercepts by absorption a certain number of them, such as our sun appears to be, we must probably regard these objects, or at least their photo-surfaces, as enormous masses of luminous gas or vapour. For it is alone from matter in the gaseous state that light consisting of certain definite refrangibilities only, as is the case with the light of these nebulae, is known to be emitted.”
Whether or not you enjoy M27 as one of the most superb planetary nebula in the night sky (or as a science object) you will 100% agree with the words of of Burnham: “The observer who spends a few moments in quiet contemplation of this nebula will be made aware of direct contact with cosmic things; even the radiation reaching us from the celestial depths is of a type unknown on Earth…”
Locating Messier 27:
When you first begin, Messier 27 will seem like such an elusive target – but with a few simple sky “tricks”, it won’t be long until you’ll be finding this spectacular planetary nebula under just about any sky conditions. The hardest part is simply sorting out all the stars in the area to know the right ones to aim at!
The way I found easiest to teach others was to start BIG. The cruciform patterns of the Cygnus and Aquila constellations are easy to recognize and can be seen from even urban locations. Once you’ve identified these two constellations, you’re going smaller by locating Lyra and the tiny kite-shape of Delphinus.
Now you’ve circled the area and the hunt for Vulpecula the Fox begins! What’s that you say? You can’t distinguish Vulpecula’s primary stars from the rest of the field? You’re right. They don’t stand out like they should, and being tempted to simply aim halfway between Albeireo (Beta Cygni) and Alpha Delphini is too much of a span to be accurate. So what are we going to do? Here’s where some patience comes into play.
If you give yourself time, you’ll begin to notice the stars of Sagitta are ever so slightly brighter than the rest of the field stars around it, and it won’t be long until you pick out that arrow pattern. In your mind, measure the distance between Delta and Gamma (the 8 and Y shape on a starfinder map) and then just aim your binoculars or finderscope exactly that same distance due north of Gamma.
The location of M27 in the constellation Vulpecula. Credit: IAU/Sky & Telescope magazine (Roger Sinnott & Rick Fienberg)
You’ll find M27 every time! In average binoculars it will appear as a fuzzy, out of focus large star in a stellar field. In the finderscope, it may not appear at all… But in a telescope? Be prepared to be blown away! And here are the quick facts on the Dumbbell Nebula to help get you started:
Object Name: Messier 27 Alternative Designations: M27, NGC 6853, The Dumbbell Nebula Object Type: Planetary Nebula Constellation: Vulpecula Right Ascension: 19 : 59.6 (h:m) Declination: +22 : 43 (deg:m) Distance: 1.25 (kly) Visual Brightness: 7.4 (mag) Apparent Dimension: 8.0×5.7 (arc min)
The rose-coloured star forming region Messier 17, captured by the Wide Field Imager on the MPG/ESO 2.2-metre telescope at ESO’s La Silla Observatory in Chile.. Credit: ESO/Subaru Telescope (NAOJ)/Hubble Space Telescope
Welcome back to Messier Monday! In our ongoing tribute to the great Tammy Plotner, we take a look at the Messier 17 nebula – aka. The Omega Nebula (and a few other names).
In the 18th century, while searching the night sky for comets, French astronomer Charles Messier began noticing a series of “nebulous objects” in the night sky. Hoping to ensure that other astronomers did not make the same mistake, he began compiling a list of these objects,. Known to posterity as the Messier Catalog, this list has come to be one of the most important milestones in the research of Deep Sky objects.
One of these is the star-forming nebula known as Messier 17 – or as it’s more famously known, the Omega Nebula (or Swan Nebula, Checkmark Nebula, and Horseshoe Nebula). Located in the Sagittarius constellation, this beautiful nebula is considered one of the brightest and most massive star-forming regions in our galaxy.
Description:
From its position in space some 5,000 to 6,000 light years from Earth, the “Omega” nebula occupies a region as large as 40 light years across, with its brightest porition covering a 15 light year expanse. Like many nebulae, this giant cosmic cloud of interstellar matter is a starforming region in the Sagittarius or Sagittarius-Carina arm of our Milky Way galaxy.
What you see is the hot hydrogen gas that is illuminated when its particles are excited by the hottest of the stars that have just formed within the nebula. Also, some of the light is being reflected by the nebula’s own dust. These remain hidden by dark obscuring material, and we know their presence only through the detection of their infrared radiation.
Image of M17 showing specific elements based on their color, including sulfur (red), hydrogen (green), oxygen (blue). Credit: NASA/Ignacio de la Cueva Torregrosa
“We report the discovery of six infrared stellar-wind bowshocks in the Galactic massive star formation regions M17 and RCW49 from Spitzer GLIMPSE (Galactic Legacy Infrared Mid-Plane Survey Extraordinaire) images. The InfraRed Array Camera (IRAC) on the Spitzer Space Telescope clearly resolves the arc-shaped emission produced by the bowshocks. We use the stellar SEDs to estimate the spectral types of the three newly-identified O stars in RCW49 and one previously undiscovered O star in M17. One of the bowshocks in RCW49 reveals the presence of a large-scale flow of gas escaping the HII region. Radiation-transfer modeling of the steep rise in the SED of this bowshock toward longer mid-infrared wavelengths indicates that the emission is coming principally from dust heated by the star driving the shock. The other 5 bowshocks occur where the stellar winds of O stars sweep up dust in the expanding HII regions.”
Is Messier 17 still actively producing stars? You bet. Even protostars have been discovered hiding in its folds. As M. Nielbock (et al), wrote in 2008:
“For the first time, we resolve the elongated central infrared emission of the large accretion disk in M 17 into a point-source and a jet-like feature that extends to the northeast. We regard the unresolved emission as to originate from an accreting intermediate to high-mass protostar. In addition, our images reveal a weak and curved southwestern lobe whose morphology resembles that of the previously detected northeastern one. We interpret these lobes as the working surfaces of a recently detected jet interacting with the ambient medium at a distance of 1700 AU from the disk centre. The accreting protostar is embedded inside a circumstellar disk and an envelope causing a visual extinction. This and its K-band magnitude argue in favour of an intermediate to high-mass object, equivalent to a spectral type of at least B4. For a main-sequence star, this would correspond to a stellar mass of 4 M.”
The location of the Omega Nebula, with other Messier objects and major stars shown. Image: Wikisky
How many new stars lay hidden inside? Far more than the famous Orion nebula may contain. So says a 2013 study produced by L. Eisa (et al):
“The complex resembles the Orion Nebula/KL region seen nearly edge-on: the bowl-shaped ionization blister is eroding the edge of the clumpy molecular cloud and triggering massive star formation, as evidenced by an ultra-compact HII region and luminous protostars. Only the most massive members of the young NGC 6618 stellar cluster exciting the nebula have been characterized, due to the comparatively high extinction. Near-infrared imagery and spectroscopy reveal an embedded cluster of about 100 stars earlier than B9. These studies did not cover the entire cluster, so even more early stars may be present. This is substantially richer than the Orion Nebula Cluster which has only 8 stars between O6 and B9.”
History of Observation:
The Omega Nebula was first discovered by Philippe Loys de Cheseaux and is just one of the six nebulae in his documents. As he wrote of his discovery:
“Finally, another nebula, which has never been observed. It is of a completely different shape than the others: It has perfectly the form of a ray, or of the tail of a comet, of 7′ length and 2′ broadth; its sides are exactly parallel and rather well terminated, as are its two ends. Its middle is whiter than the border.” Because De Cheseaux’s work wasn’t widely read, Charles Messier independently rediscovered it on June 3, 1764 and cataloged it in his own way: “In the same night, I have discovered at little distance of the cluster of stars of which I just have told, a train of light of five or six minutes of arc in extension, in the shape of a spindle, and in almost the same as that in the girdle of Andromeda; but of a very faint light, not containing any star; one can see two of them nearby which are telescopic and placed parallel to the Equator: in a good sky one perceives very well that nebula with an ordinary refractor of 3 feet and a half. I have determined its position in right ascension of 271d 45′ 48″, and its declination of 16d 14′ 44” south.“
Omega Nebula sketch by John Herschel, 1833. Credit: messier-objects.com
By historical accounts, it was Sir William Herschel who may have truly had a little bit of insight on what this object might one day mean when he observed it on his own and reported:
“1783, July 31. A very singular nebula; it seems to be the link to join the nebula in Orion to others, for this is not without a possibility of being stars. I think a great deal more of light and a much higher power would be of service. 1784, June 22 (Sw. 231). A wonderful nebula. Very much extended, with a hook on the preceding [Western] side; the nebulosity of the milky kind; several stars visible in it, but they seem to have no connection with the nebula, which is far more distant. I saw it only through short intervals of flying clouds and haziness; but the extent of the light including the hook is above 10′. I suspect besides, that on the following [Eastern] side it goes on much farther and diffuses itself towards the north and south. It is not of equal brightness throughout and has one or more places where the milky nebulosity seems to degenerate into the resolvable [mottled] kind; such a one is that just following the hook towards the north. Should this be confirmed on a very fine night, it would bring on the step between these two nebulosities which is at present wanting, and would lead us to surmise that this nebula is a stupendous stratum of immensely distant fixed stars, some of whose branches come near enough to us to be visible as a resolvable nebulosity, while the rest runs on to so great a distance as only to appear under the milky form.”
So where did the name “Omega Nebula” come from? That credit goes to John Herschel, who stated in his observing notes:
“The figure of this nebula is nearly that of the Greek capital Omega, somewhat distorted and very unequally bright. It is remarkable that this is the form usually attributed to the great nebula in Orion, though in that nebula I confess I can discern no resemblence whatever to the Greek letter. Messier perceived only the bright preceding branch of the nebula now in question, without any of the attached convolutions which were first noticed by my Father. The chief peculiarities which I have observed in it are, 1st, the resolvable knot in the following portion of the bright branch, which is in a considerable degree insulated from the surrounding nebula; strongly suggesting the idea of an absorption of nebulous matter; and 2ndly, the much feebler and smaller knot in the north preceding end of the same branch, where the nebula makes a sudden bend at an acute angle. With a view to a more exact representation of this curious nebula, I have at different times taken micrometrical measures of the relative places of the stars in and near it, by which, when laid down on the chart, its limits may be traced and identified, as I hope soon to have better opportunity to do than its low situation in this latitudes will permit.”
Infrared images of M17, taken by the Spitzer Space Telescope. Credit: NASA/JPL-Caltech/M. Povich (Univ. of Wisconsin)
Locating Messier 17:
Because M17 is both large and quite bright, its distinctive “2” shape isn’t hard to make out in optics of any size. For binoculars and image correct finderscopes, try starting with the constellation of Aquila and begin tracing the stars down the eagle’s back to Lambda. When you reach that point, continue to extend the line through to Alpha Scuti, then southwards towards Gamma Scuti. M16 is slightly more than 2 degrees (about a fingerwidth) southwest of this star.
If you are in a dark sky location, you can also identify it easily in binoculars by starting at the M24 “Star Cloud”, north of Lambda Sagittari (the teapot lid star), and simply scanning north. This nebula is bright enough to even cut through moderately light polluted skies with ease, but don’t expect to see it when the Moon is nearby. You’ll enjoy the rich starfields combined with an interesting nebula in binoculars, while telescopes will easily begin resolving the interior stars.
And here are the quick facts on M17 for your convenience:
Object Name: Messier 17 Alternative Designations: M17, NGC 6618, Omega, Swan, Horseshoe, or Lobster Nebula Object Type: Open Star Cluster with Emission Nebula Constellation: Sagittarius Right Ascension: 18 : 20.8 (h:m) Declination: -16 : 11 (deg:m) Distance: 5.0 (kly) Visual Brightness: 6.0 (mag) Apparent Dimension: 11.0 (arc min)
And be sure to enjoy this video from the European Southern Observatory (ESO) that shows this nebula in all its glory:
