Posted on by Tammy Plotner

The Coma Berenices Constellation

The northern constellation known as Coma Berenices. Credit and Copyright: © 2003 Torsten Bronger.

Welcome back to Constellation Friday! Today, in honor of the late and great Tammy Plotner, we will be dealing with “Berenice’s Hair” – the Coma Berenices constellation!

In the 2nd century CE, Greek-Egyptian astronomer Claudius Ptolemaeus (aka. Ptolemy) compiled a list of all the then-known 48 constellations. This treatise, known as the Almagest, would be used by medieval European and Islamic scholars for over a thousand years to come, effectively becoming astrological and astronomical canon until the early Modern Age.

One of these is the constellation Coma Berenices, an ancient constellation located in the norther skies. In the Almagest, Ptolemy considered the asterism to be part of the constellation Leo. Today, it is one of the 88 constellations recognized by the International Astronomical Union, and is bordered by the constellations of Canes Venatici, Ursa Major, Leo, Virgo and Boötes.

Name and Meaning:

In mythology, it is easy to see why this dim collection of stars was once associated with Leo and considered to be the tuft of hair at the end of the Lion’s tail. However, as the years passed, a charming legend grew around this sparkling group of stars. Since the time of Ptolemy, this grouping of stars was recognized and although he didn’t list it as one of his 88 constellations, he did refer to is as “Berenice’s Hair”.

Coma Berenices as seen by the naked eye. Credit: Till Credner/ AlltheSky.com

As legend would have it, the good Queen Berenice II of Egypt offered to sacrifice her beautiful long hair to Aphrodite for the safe return of her husband from battle. When she cut off her locks and placed it on the altar and returned the next day, her sacrifice was gone. To save his life, the court astronomer proclaimed Aphrodite had immortalized Berenice’s gift in the stars… and thus the Lion lost his tail and the astronomer saved his hide!

History of Observation:

Like many of the 48 constellations recognized by Ptolemy, Coma Berenices traces it routes back to ancient Mesopotamia. To Babylonian astronomers, it was known as Hegala, which translated to “which is before it”. However, the first recorded mention comes from Conon of Samos, the 3rd century BCE court astronomer to Ptolemy III Euergetes – the Greek-Egyptian king. It was named in honor of his consort, Berenice II, who is said to have cut off her long hair as a sacrifice to ensure the safety of the king.

The constellation was named “bostrukhon Berenikes” in Greek, which translates in Latin to “Coma Berenices” (or “Berenice’s hair”). Though it was previously designated as its own constellation, Ptolemy considered it part of Leo in his 2nd century CE tract the Almagest, where he called it “Plokamos” (Greek for “braid”). The constellation was also recognized by many non-western cultures.

In Chinese astronomy, the stars making up Coma Berenices belonged to two different areas – the Supreme Palace Enclosure and the Azure Dragon of the East. Eighteen of the constellation’s stars were in an area known as Lang wei (“seat of the general”). To Arabic astronomers, Coma Berenices was known as Al-Du’aba, Al Dafira and Al-Hulba, forming the tuft of the constellation Leo (consistent with Ptolemy’s designation).

Fragment of Mercator’s 1551 celestial globe, showing Coma Berenices. Credit: Harvard Map Collection

By the 16th century, the constellation began to be featured on globes and maps produced by famed cartographers and astronomers. In 1602, Tycho Brahe recognized it as its own constellation and included it in his star catalogue. In the following year, it was included in Johann Bayer’s famed celestial map, Uranometria. In 1920, it was included by the IAU in the list of the 88 modern constellations.

Notable Objects:

Despite being rather dim, Coma Berenices is significant because it contains the location of the North Galactic Pole. It is comprised of only 3 main stars, but contains 44 Bayer/Flamsteed designated members. Of its main stars, Alpha Comae Berenices (aka. Diadem) is the second-brightest in the constellation.

The name is derived from the Greek word diádema, which means “band” or “fillet”, and represents the gem in Queen Berenice’s crown. It is sometimes known by its other traditional name, Al-Zafirah, which is Arabic for “the braid”. It is a binary star composed of two main sequence F5V stars that are at a distance of 63 light years from Earth.

The Black Eye Galaxy (Messier 64). Credit: NASA/The Hubble Heritage Team (AURA, STScI)

It’s brightest star, Beta Comae Berenices, is located 29.78 light years from Earth and is a main sequence dwarf that is similar to our Sun (though larger and brighter). It’s third major star, Gamma Comae Berenices, is a giant star belonging to the spectral class K1II and located about 170 light years from Earth.

Coma Berenices is also home to several Deep Sky Objects, which include spiral galaxy Messier 64. Also known as the Black Eye Galaxy (Sleeping Beauty Galaxy and Evil Eye Galaxy), this galaxy is located approximately 24 million light years from Earth. This galaxy has a bright nucleus and a dark band of dust in front of it, hence the nicknames.

Then there is the Needle Galaxy, which lies directly above the North Galactic Pole and was discovered by Sir William Herschel in 1785. It is one of the most famous galaxies in the sky that can be viewed edge-on. It lies at a distance of about 42.7 million light years from Earth and is believed to be a barred spiral galaxy from its appearance.

Coma Berenices is also home to two prominent galaxy clusters. These includes the Coma Cluster, which is made up of about 1000 large galaxies and 30,000 smaller ones that are located between 230 and 300 million light years from Earth. South of the Coma Cluster is the northern part of the Virgo Cluster, which is located roughly 60 million light years from Earth.

The globular cluster Messier 53 (NGC 5024), located in the Coma Berenices constellation. Credit: NASA (Wikisky)

Other Messier Objects include M53, a globular cluster located approximately 58,000 light years away; Messier 100, a grand design spiral galaxy that is one of the brightest members of the Virgo cluster (located 55 million light years away); and Messier 88 and 99 – a spiral galaxy and unbarred spiral galaxy that are 47 million and 50.2 million light years distant, respectively.

Finding Coma Berenices:

Coma Berenices is best visible at latitudes between +90° and -70° during culmination in the month of May. There is one meteor shower associated with the constellation of Coma Berenices – the Coma Berenicid Meteor shower which peaks on or near January 18 of each year. Its fall rate is very slow – only one or two per hour on average, but these are among the fastest meteors known with speeds of up to 65 kilometers per second!

For both binoculars and telescopes, Coma Berenices is a wonderland of objects to be enjoyed. Turn your attention first to the brightest of all its stars – Beta Coma Berenices. Positioned about 30 light years from Earth and very similar to our own Sun, Beta is one of the few stars for which we have a measured solar activity period – 16.6 years – and may have a secondary activity cycle of 9.6 years.

Now look at slightly dimmer Alpha. Its name is Diadem – the Crown. Here we have a binary star of equal magnitudes located about 65 light years from our solar system, but it’s seen nearly “edge-on” from the Earth. This means the two stars appear to move back-and-forth in a straight line with a maximum separation of only 0.7 arcsec and will require a large aperture telescope with good resolving power to pull them apart. If you do manage, you’re separating two components that are about the distance of Saturn from the Sun!

The location of the northern constellation Coma Berenices. Credit: IAU/Sky&Telescope magazine

Another interesting aspect about singular stars in Coma Berenices is that there are over 200 variable stars in the constellation. While most of them are very obscure and don’t go through radical changes, there is one called FK Comae Berenices which is a prototype of its class. It is believed that the variability of FK Com stars is caused by large, cool spots on the rotating surfaces of the stars – mega sunspots! If you’d like to keep track of a variable star that has notable changes, try FS Comae Berenices (RA 13 3 56 Dec +22 53 2). It is a semi-regular variable that varies between 5.3m and 6.1 magnitude over a period of 58 days.

For your eyes, binoculars or a rich field telescope, be sure to take in the massive open cluster Melotte 111. This spangly cloud of stars is usually the asterism we refer to as the “Queen’s Hair” and the area is fascinating in binoculars. Covering almost 5 full degrees of sky, it’s larger than most binocular fields, but wasn’t recognized as a true physical stellar association until studied by R.J. Trumpler in 1938.

Located about 288 light years from our Earth, Melotte 111 is neither approaching nor receding… unusual – but true. At around 400 million years old, you won’t find any stars dimmer than 10.5 magnitude here. Why? Chances are the cluster’s low mass couldn’t prevent them from escaping long ago…

Now turn your attention towards rich globular cluster, Messier 53. Achievable in both binoculars and small telescopes, M53 is easily found about a degree northwest Alpha Comae. At 60,000 light years away from the galactic center, it’s one of the furthest globular clusters away from where it should be. It was first discovered by Johann Bode in 1755, and once you glimpse its compact core you’ll be anxious to try to resolve it.

The Needle Galaxy (NGC 4565). Credit: ESO

With a large telescope, you’ll notice about a degree further to the east another globular cluster – NGC 5053 – which is also about the same physical distance away. If you study this pair, you’ll notice a distinct difference in concentrations. The two are very much physically related to one another, yet the densities are radically different!

Staying with binoculars and small telescopes, try your hand at Messier 64 – the “Blackeye Galaxy”. You’ll find it located about one degree east/northeast of 35 Comae. While it will be nothing more than a hazy patch in binoculars, smaller telescopes will easily reveal the signature dustlane that makes M64 resemble its nickname. It is one of the brightest spiral galaxies visible from the Milky Way and the dark dust lane was first described by Sir William Herschel who compared it to a “Black Eye.”

Now put your telescope on Messier 100 – a beautiful example of a grand-design spiral galaxy, and one of the brightest galaxies in the Virgo Cluster. This one is very much like our own Milky Way galaxy and tilted face-on, so we may examine the spiral galaxy structure. Look for two well resolved spiral arms where young, hot and massive stars formed recently from density perturbations caused by interactions with neighboring galaxies. Under good observing conditions, inner spiral structure can even be seen!

Try lenticular galaxy Messier 85. In larger telescopes you will also see it accompanied by small barred spiral NGC 4394 as well. Both galaxies are receding at about 700 km/sec, and they may form a physical galaxy pair. How about Messier 88? It’s also one of the brighter spiral galaxies in the Virgo galaxy cluster and in a larger telescope it looks very similar to the Andromeda galaxy – only smaller.

How about barred spiral galaxy M91? It’s one of the faintest of the Messier Catalog Objects. Although it is difficult in a smaller telescope, its central bar is very strong in larger aperture. Care to try Messier 98? It is a grand edge-on galaxy and may or may not be a true member of the Virgo group. Perhaps spiral galaxy Messier 99 is more to your liking… It’s also another beautiful face-on presentation with grand spiral arms and a sweeping design that will keep you at the eyepiece all night!

There are other myriad open clusters and just as many galaxies waiting to be explored in Coma Berenices! It’s a fine region. Grab a good star chart and put a pot of coffee on to brew. Comb the Queen’s Hair for every last star. She’s worth it.

We have written many interesting articles about the constellation here at Universe Today. Here is What Are The Constellations?, What Is The Zodiac?, and Zodiac Signs And Their Dates.

Be sure to check out The Messier Catalog while you’re at it!

For more information, check out the IAUs list of Constellations, and the Students for the Exploration and Development of Space page on Canes Venatici and Constellation Families.

Source:

Posted on by Tammy Plotner

Midnight At The OPT Corral: Shootout Between The Celestron SkyScout and Meade MySKY

It’s midnight on the plains of Ohio. A lone tumbleweed rolls across the backyard – or maybe it’s just a black german shepherd skulking about in the starlight. A mysterious figure dressed in black steps off the deck planks and out into the open. She’s come fully armed and ready to duel it out. But this time it isn’t the classic battle between the McClaurys and Clantons versus the Earps and Doc Holliday… It’s a shootout between a Celestron SkyScout and a Meade mySKY.

There isn’t any spurs to chink on my tennis shoes as I make my way out across the open back field. However, I am just strange enough to be dressed in a black leather duster and a borrowed black leather fedora and I’m doing my best cowboy swagger as I mosey my way towards the fence row where I’d earlier hung a cardboard sign that proclaimed it to be the “OPT Corral”. I’m in the wide, wide open now… Armed with fresh batteries and the latest technology. I want my questions answered and I want to give those answers to you.

Ready… Set… Aim… Shoot!

Hands down, the Meade mySKY is the single coolest astronomy gadget I’ve ever used. The second it turned on I was hopelessly, helplessly in love with the graphics, music and program. Five minutes later I had a short in the audio cable and when I tried to turn it off the button stuck and even at the risk of getting dew and grass on my good leather coat I had to sit down and take the batteries out to fix it. Once done, everything reset, and we were good to go again, but the nagging problem with a slight short in the audio cord persisted. Still… It’s terminally cool. Every time I would aim it at something I would have this vision of Carl Sagan out there with me, wandering through the weeds, puffing away and aiming a ray gun at the night sky. Hollywood all the way, baby… The multi-media presentations are simply stunning (and after awhile, annoying) and I can say without a doubt that for anyone who even remotely has an interest in astronomy that you’d love it, too.

Ready… Set… Aim… Shoot!

The Celestron SkyScout has about all the visual appeal of a chubby chick at a dance – but take it from a chubby chick at a dance – we’re the type you want to meet. Yep, we aren’t glamorous – but we don’t short out and we’re still on the same batteries you put in us over a year ago. We’re not “wowing” you with fifteen minute video on everything you wanted to know about the Moon but were afraid to ask, but guess what? We’re not blinding you either. We’re just a nice sturdy little box with a pleasant voice that explains an object when wanted and needed, and gives a red scrolling readout when wanted and needed. Same goes with the other… But not all the time, you see. No matter how many times you turn it off and on, or have to take the batteries out to turn it off and on, you have to go through the initial video presentation. But I digress…

Ready… Set… Aim… Shoot!

Once you’ve learned to use the Meade mySKY functions, you can dim the screen and change it over to night vision mode. However, I will warn you that even very dim and red, it is still like pointing your cell phone screen at the sky. Personally, I found it blinding and had to cover it with my hand to aim. The aiming mechanism itself is also a little difficult. It is three illuminated red marks, like a reflex sight, which can either be static or blinking. The problem is, when you go for a tight star field? The sights cover the stars and you can’t see where you’re aimed! To be fair, the Celestron SkyScout has somewhat solved that problem. By looking through the SkyScout (similar to a camcorder) you are seeing an unmagnified view of the night sky and you have an illuminated (brightness adjustable) red exterior circle. Again, this is considerably better, but not perfect. The screen does dim the stellar factor, so there’s no absolute solution besides preference.

Ready… Set… Aim… Shoot!

Score in the favor of the Meade mySKY. In this case I feel that its internal GPS system picked up on my location faster than the Celestron SkyScout and didn’t seem to notice when I walked it closer to metal. Odd, but true. In both cases, some operations are absolutely identical, because both pieces of equipment are capable of driving each companies respective telescopes. However, out here in the back fields, drivin’ the scopes ain’t what I’m after… It’s drivin’ the stars.

Ready… Set… Aim… Shoot!

Now we’re down to that good old classic saying – “the brass tacks”. In other words, what’s my opinion and why. Well, I ain’t afraid of no buzzards, so I’m going to give it to you.

If you want totally cool, get the Meade mySKY. It goes through all the same motions as the other, plus it has all the multi-media programming that any techno-geek could ever want. As a word of caution, I would also assess it as not very durable and somewhat annoying in the long run. It’s damn fancy, Frank… Kinda’ like a silver Colt revolver with trimmins’….

If you want long-term service, get the Celestron SkyScout. It lacks the bells and whistles, but also lacks the techno-problems that goes with them. It has proven itself to be highly durable and practical, perhaps a bit boring, but a useful astronomy tool. It’s a Glock, George… Plain and simple.

Shoot ’em both and decide.

Addendum: OPT has announced that due to the popular nature of this article, they have reduced the price of the Celestron SkyScout to $199 and a Meade mySKY will now be offered at $149 with free shipping.

Many thanks to Oceanside Photo and Telescope for providing the Meade mySKY and allowing me to use OPT as part of the ‘shoot out’ idea.

Posted on by Tammy Plotner

Weekend SkyWatcher’s Forecast – October 24-26, 2008

Greetings, fellow SkyWatchers! It’s a dark sky weekend and a great time to get out your binoculars or telescopes and enjoy. Use bright star – Formalhaut – to help you find distant planet Uranus… and the “Great Square of Pegasus” to help you find an even more distant galaxy! Would you like to explore some stellar evolution or did you know Saturn was back in the morning skies? Then check out what’s happening as we head out into the night…

Friday, October 24, 2008 – Today we remember the launch of Deep Space 1 from Cape Canaveral in 1998. Its primary mission was extremely successful, testing a dozen advanced, high-risk technologies. During its extended mission, Deep Space 1 headed for Comet Borrelly and sent back the best images from a comet up to that time. The mission continued to test new techniques until it was finally retired after three fantastic years of service on December 18, 2001.

Tonight in 1851, a busy astronomer was at the eyepiece as William Lassell discovered Uranus’ moons Ariel and Umbriel. Although the equipment he used is far beyond backyard equipment, we can have a look at that distant world, as we find Uranus about 25 degrees (slightly more than an hand span) north-northwest of Fomalhaut.

While Uranus’ small, blue-green disc isn’t exactly the most exciting thing to see in a small telescope or binoculars, the very fact we are looking at a planet that’s over 18 times further from the Sun than we are is pretty impressive! Usually holding close to magnitude 6, we watch as the tilted planet orbits our nearest star once every 84 years. Its atmosphere is composed of hydrogen, helium and methane, yet pressure causes about a third of this distant planet to behave as a liquid. Larger telescopes may be able to discern a few of Uranus’ moons, for Titania (the brightest) is around magnitude 14.

Now let’s head toward the southwest corner star of the Great Square of Pegasus – Alpha. Our goal will be 11th magnitude NGC 7479, located about three degrees south (RA 23 04 56 Dec +12 19 23).

Discovered by Sir William Herschel in 1784 and cataloged as H I.55, this barred spiral galaxy can be spotted in average telescopes and comes to beautiful life with larger aperture. Also known as Caldwell 44 on Sir Patrick Moore’s observing list, what makes this galaxy special is its delicate “S” shape. Smaller scopes will easily see the central bar structure of this 105 million light-year distant island universe, and as aperture increases, the western arm will become more dominant. This arm itself is a wonderful mystery – containing more mass than it should and having a turbulent structure. It is believed that a minor merger may have occurred at one time, yet no evidence of a companion galaxy can be found.

On July 27, 1990, a supernova occurred near NGC 7479’s nucleus and reached a magnitude of 16. When observed in the radio band, there is a polarized jet near the bright nucleus that is unlike any other structure known. If at first you do not see a great deal of detail, relax… Allow your mind and eye time to look carefully. Even with telescopes as small as 8-10″, structure can easily be seen. The central bar becomes “clumpy” and this well-studied Seyfert galaxy is home to an abundance of molecular gas and is actively forming stars. Enjoy the incredible NGC 7479…

Saturday, October 25, 2008 – And who was watching the planets in 1671? None other than Giovanni Cassini – because he’d just discovered Saturn’s moon Iapetus. If you’re up before dawn this morning, have a look at Saturn for yourself as it poses less than five degrees away from the Moon. Iapetus usually holds around a magnitude of 12, and orbits well outside of bright Titan’s path.

Today is the birthday of Henry Norris Russell. Born in 1877, Russell was the American leader in establishing the modern field of astrophysics. As the namesake for the American Astronomical Society’s highest award (for lifetime contributions to the field), Mr. Russell is the “R” in H-R diagrams, along with Mr. Hertzsprung. This work was first used in a 1914 paper, published by Russell.

Tonight let’s start with a star that resides right in the middle of the H-R diagram as we have a look Beta Aquarii (RA 21 31 33 Dec -05 34 16).

Named Sadal Suud (“Luck of Lucks”), this star of spectral type G star is around 1030 light-years distant from our solar system and shines 5800 times brighter than our own Sun. The main sequence beauty also has two 11th magnitude optical companions. The one closest to Sadal Suud was discovered by John Herschel in 1828, while the further star was reported by S. W. Burnham in 1879.

Now let’s head to the eastern portion of Capricornus and start by identifying Zeta about a fistwidth southwest of the eastern corner star – Delta. Now look southeast about two fingerwidths to identify 5th magnitude star 41. About one half degree west is our target globular for the evening, M30 (RA 21 40 22 Dec -23 10 44).

At near magnitude 8, this class V globular cluster is well suited to even binoculars, and becomes spectacular in a telescope. Originally discovered by Messier in August 1764, and resolved by William Herschel in 1783, M30’s most attractive features include the several branches of stars which seem to radiate from its concentrated core region. Estimated to be about 26,000 light-years away, you’ll find it fairly well resolved in large aperture, but take time to really look. The dense central region may have already undergone core collapse – yet as close as these stars are, very few have collided to form x-ray binaries. For the smaller scope, notice how well M30’s red giants resolve, and be sure to mark your notes!

Sunday, October 26, 2008 – If you’re up early, be sure to look for Venus and Antares making a close pairing in the pre-dawn sky!

Tonight it’s time for a telescopic challenge – a compact galaxy group. You’ll find it less than half a degree southeast of the stellar pair 4 and 5 Aquarii (RA 20 52 26 Dec -05 46 19).

Known as Hickson 88, this grouping of four faint spiral galaxies is estimated to be about 240 million light-years away and is by no means an easy object – yet the galactic cores can just be glimpsed with mid-sized scopes from a very dark site. Requiring around 12.5″ to study in detail, you’ll find the brightest of the group to be northernmost NGC 6978 and NGC 6977. While little detail can be seen in the average large backyard scope, NGC 6978 shows some evidence of being a barred spiral, while NGC 6977 shows the even appearance of a face-on. Further south, NGC 6976 is much smaller and considerably fainter. It is usually caught while averting and studying the neighborhood. The southernmost galaxy is NGC 6975, whose slender, edge-on appearance makes it much harder to catch.

Although these four galaxies seem to be in close proximity to one another, no current data suggests any interaction between them. While such a faint galaxy grouping is not for everyone, it’s a challenge worthy of seasoned astronomer with a large scope! Enjoy…

Until next week, ask for the moon – but keep on reaching for the stars!

This week’s awesome images are: Deep Space 1 image of Comet Borrelly – Credit: NASA, Rendition of Lassell’s Telescope (widely used public image), Uranus – Credit: HST/NASA, NGC 7479 – Credit: Palomar Observatory, courtesy of Caltech, Henry Norris Russell (widely used public image), Beta Aquarii – Credit: Palomar Observatory, courtesy of Caltech, M30 – REU program/NOAO/AURA/NSF and Hickson 88 – Credit: Palomar Observatory, courtesy of Caltech. Thank you so much!!

Posted on by Tammy Plotner

Dark Knight Ahead – B33 by Gordon Haynes

If you live in the northern hemisphere, I’m sure you’ve very much noticed the daylight hours have become much shorter – but have you noticed the return of the winter stars during the early morning hours? If you’re up before dawn the constellation of Orion sits high in the sky and with it brings promises of “Dark Knight Ahead”….

In this beautiful h-alpha image of B33 and NGC2024 taken by Gordon Haynes, we’re getting a preview of one of the most sought after dark nebulae in the heavens – the “Horsehead”. The long tongue of nebulosity which makes it visible is IC 434, first discovered photographically by Edward Pickering in 1889. But it wasn’t until January 25, 1900 that Isaac Roberts picked up the dark notch on a photo he’d made and E.E. Barnard visually recognized it around 1910.

The ever-vigilant, and visually astute Barnard made his first publication of the “dark knight” in Dark Regions in the Sky Suggesting an Obscuration of Light – Astrophysical Journal, Vol. 38, pages 496-501. In 1919, he officially cataloged it as B33 in On the Dark Markings of the Sky – with a Catalogue of 181 Such Objects where it remains to this day as an astronomical favorite. What makes this 1,600 light year distant dark globule of dust and non-luminous gas so important? Well, a recent study done using the h-alpha wavelength and the 2.34 m Vainu Bappu Telescope were done to test fractal structure. Ten sample readings of the box dimension of this image were taken using a fractal analysis software, giving an average value of 1.6965725. The sample dimensions were found to be different from the topological dimension of one. Importantly, the box dimension of B 33 was not found to be significantly different from that of the Julia set (box dimension 1.679594) with c = -0.745429 + 0.113008i. This provides compelling evidence to show that the structure of the Horsehead nebula is not only fractal, but also that its geometry can be described by the Julia function f(z) = z2 + c, where both z and c are complex numbers.

While that’s cool, I wanted to go even deeper. I checked into SCUBA and this is what I found from the works of D. Ward-Thompson (et al):

“We present observations taken with SCUBA on the JCMT of the Horsehead Nebula in Orion (B33), at wavelengths of 450 and 850 mum. We see bright emission from that part of the cloud associated with the photon-dominated region (PDR) at the `top’ of the horse’s head, which we label B33-SMM1. We characterise the physical parameters of the extended dust responsible for this emission, and find that B33-SMM1 contains a more dense core than was previously suspected. We compare the SCUBA data with data from the Infrared Space Observatory (ISO) and find that the emission at 6.75-mum is offset towards the west, indicating that the mid-infrared emission is tracing the PDR while the submillimetre emission comes from the molecular cloud core behind the PDR. We calculate the virial balance of this core and find that it is not gravitationally bound but is being confined by the external pressure from the HII region IC434, and that it will either be destroyed by the ionising radiation, or else may undergo triggered star formation. Furthermore we find evidence for a lozenge-shaped clump in the `throat’ of the horse, which is not seen in emission at shorter wavelengths. We label this source B33-SMM2 and find that it is brighter at submillimetre wavelengths than B33-SMM1. SMM2 is seen in absorption in the 6.75-mum ISO data, from which we obtain an independent estimate of the column density in excellent agreement with that calculated from the submillimetre emission. We calculate the stability of this core against collapse and find that it is in approximate gravitational virial equilibrium. This is consistent with it being a pre-existing core in B33, possibly pre-stellar in nature, but that it may also eventually undergo collapse under the effects of the HII region.”

So it’s a chance thing… It just happens to look like a cosmic chess piece. But this is one chess piece that has the odds stacked in its favor for starbirth. This shapely cloud of H2 molecules may have a density within its internal clumps that could reach up to 105 H2 per cubic centimeters or more and have their own internal magnetic field which will provides support against their own gravity. Deep inside, the dust blocks out the stellar ultraviolet radiation, getting darker and colder – just like our northern hemisphere nights. Near the center, the carbon changes and the chemistry becomes exotic – stars begin to form in a process very similar to condensation. The pressure appears to be building inside B33…

And tomorrow’s “Dark Knight” will be lit by new stars.

Many thanks to AORAIA member Gordon Haynes for the fine photograph!

Posted on by Tammy Plotner

The Vixen ED100SF Refractor – Superb Optical Quality

So here we go. There’s a knock on the door and a big box arrives. It’s either a coffin for a short, skinny person or I’ve got another telescope on my hands. I wrestled it up on my dining room table, carefully cut the packing tape and revealed the shiny aluminum case that lay beneath the brown cardboard layer with the word Vixen stamped on the outside. Vixen? Haven’t we met somewhere before in another life?

For those of you who know me, you know I’m not much of a refractor person, although I own several. The reason isn’t because I don’t like refractors, it’s because I’m primarily a faint galaxy and comet hunter and to get the aperture I need I simply can’t afford a refractor that size. However, I am also not adverse to being a sometimes “optical connoisseur” and there have been times in my life that I’ve been talked into doing things that I probably had no business doing…. and that’s how I first got introduced to Vixen refractors. To make a long story short, a friend of mine in California coerced me into purchasing an old 4″ Vixen refractor for him from a total (spooky) stranger just because he happened to live in Ohio and I’m the one that ended up footing the bill, packing this anitque across country in a self-made case fashioned from PVC pipe and loving it to death.

And now there’s another one here.

Of course, my first experience with a circa 1980 Vixen refractor certainly didn’t prepare me for today’s modern optics. When I unlatched the clean, neat aluminum case that comes standard with the Vixen – ED100SF I was blown away with the fit and finish of the product itself. Who doesn’t love a brand new telescope with a perfect white finish and all the trimmings packed neatly inside custom foam? Everything looks good, right down to the scope rings and Crayford focuser – but the bottom line isn’t looks – it’s performance. In the long run, I had some serious issues with yesteryear’s Vixen refractor and what I want to know is how today’s Vixen performs.

One of the first things you need to realize is the Vixen ED100SF isn’t a complete telescope. While most of you probably are aware of what an optical tube assembly is, I want to be fair and point out to others that it is only the telescope body with the focuser and mounting rings. In order to keep costs down, optical tube assemblies are offered to those who already have several mounts, tripods and finderscopes – along with a wide variety of eyepieces. This allows folks like me (and many of you) to afford telescopes like the Vixen refractor by making use of things we already have. In this case, the Vixen ED100SF needs to be mounted on something capable of supporting at least 14 pounds, and I happen to have several equatorial mounts capable of filling the bill – along with many different styles of finderscopes and eyepieces to use.

Now that we’re set up, are we ready to check out those optics?

As I said, once upon a time I had issues with Vixen optics – very specifically with chromatic aberration. This is also a reason why I am a reflector person. I do not like color fringing. You give me purple and I’ll tell you you’re giving me poo. Sure. Once upon a time, they tried to correct chromatic aberration by increasing the focal length. This made for great magnification powers and also made for terribly long telescopes. But, purple images or not, I loved that old Vixen… Would the new one behave the same?

The answer is no. Thanks to today’s extra low dispersion glass with its little element of flourite, there simply isn’t any unwanted color in the image. Now when I look at something, the only purple haze I get is if I’m listening to Jimi Hendrix on the ipod. All of those red, green, and blue wavelengths are coming right together in perfect, crisp focus and the image is absolutely razor sharp. Where once I might have called something a little bit “muzzy”, there is only perfection. And it isn’t even a stellar image!

The real test of the Vixen ED100SF comes with a perfect airy disk around Vega. Go ahead, do Epsilon! It’s perfect and clean. Go ahead and do a more difficult one, like Gamma Andromeda – because you’ll see there’s three stars there instead of just two. Put your backside down on my observing chair here and watch Jupiter for awhile. Again, even though I am not much of a refractor person or a planetary observer – I could really get to liking views like this! When a galiean moon comes out of eclipse and you can pick out what looks to be a hair-fine line of black between Jupiter’s limb and the satellite’s limb? What can you say besides “Wow!” The Crayford focuser is as smooth as glass and the optical quality of the telescope remains through every eyepiece I put in it. Wait a week and watch the Moon. No false colors there. Just deep dark craters and perfect definition.

On deep sky performance, I can only be honest. Here, the Vixen ED100SF only performs like a 4″ telescope. It doesn’t resolve globular clusters or galaxies any better than a similar sized reflector telescope. However, I must be fair and say that I am not an astrophotographer. I can only imagine that the high quality images that I was getting in planetary and double star performance would carry through equally should you wish to image deep sky with this baby. Since the color correction is absolutely outstanding, I can only imagine what would happen if it were combined with the correct filters and timed exposures to pick out HII regions in those distant galaxies I so admire. On open clusters, the Vixen ED100SF also gave precision performance. Objects like NGC 7790 were virtual pinpoints and that’s a nice thing to see in any telescope. In side by side comparisons with a Genesis refractor and a Takahashi, I could see no difference in optical performance visually.

At one time the Vixen ED100SF cost in excess of $1200, making it not the type of telescope for everyone. But now, prices have come to $799. Still, not the type of telescope for everyone, but definitely within the range of those interested in superb optical quality. Vixen has definitely come a long way over the years and like that Vixen telescope I delivered to a man in California so long ago…

I don’t want to give it back.

The Vixen ED100SF Refractor was kindly provided for this review by Oceanside Photo and Telescope. Our many thanks for the use of this very fine telescope!

Posted on by Tammy Plotner

Weekend SkyWatcher’s Forecast – October 10-12, 2008

Greetings, fellow Skywatchers! It’s Friiiiday! Are you ready for the weekend? Sure, it’s going to be a rather moony affair, but that doesn’t mean we can’t enjoy. Why not take the time to hunt down Neptune, or check out a cool crater like Letronne? We can always shoot for a binary star – or two – or just enjoy the solitary pleasures of being alone with Formalhaut. If you’re up to it, we’ll chase the rays from crater Bessel and try our luck with a new variable star. Don’t spend the last few good nights of the year inside hiding… Let’s rock the night together.

Friday, October 10, 2008 – Today in 1846, William Lassell was busy at his scope as he made a new discovery – Neptune’s moon Triton. Although our everyday equipment can’t “see” Triton, we can still have a look at Neptune which is also hanging out in tonight’s study constellation of Capricornus less than degree south of the Moon. Try checking astronomy periodicals or many great online sites for accurate locator charts. For some lucky astronomers, it will be an occultation event!

Tonight we’ll let Gassendi be our guide as we head north to examine the ruins of crater Letronne. Sitting on a broad peninsula on the south edge of Oceanus Procellarum, this class V crater once spanned 118 kilometers. Thanks to the lava flows which formed Procellarum, virtually the entire northern third of the crater was submerged, leaving the remaining scant walls to rise no more than a thousand meters above the surface. While this might seem shallow, it’s as high as El Capitan in Yosemite.

Although tonight’s bright skies will make our next target a little difficult to find visually, look around four fingerwidths southwest of Delta Capricorni (RA 21 26 40 Dec -22 24 40) for Zeta…

Also known as 34 Capricorni, Zeta is a unique binary system. Located about 398 light-years from Earth, the primary star is a yellow supergiant with some very unusual properties – it’s the warmest, most luminous barium star known. But that’s not all, because the B component is a white dwarf almost identical in size to our own Sun!

Saturday, October 11, 2008 – If you journey to the Moon tonight, you might return to the southern quadrant along the terminator to have a look at 227 kilometer diameter crater Schickard. You’ll easily note this crater for its smooth gray floor and eye-like appearance. Seen on the oblique, this great crater’s floor is so humped in the middle that you could stand there and not see the crater walls! Be sure to note Schickard for your lunar challenge studies. It’s a fine one!

After having looked at the Moon, take the time out to view a bright southern star – Fomalhaut (RA 22 57 39 Dec -29 37 20). Also known as “The Lonely One,” Alpha Piscis Austrini seems to sit in a rather empty area in the southern skies, some 23 light-years away. At magnitude 1, this main sequence A3 giant is the southernmost visible star of its type for northern hemisphere viewers, and is the 18th brightest star in the sky. The Lonely One is about twice the diameter of our own Sun, but 14 times more luminous! Just a little visual aid is all that it takes to reveal its optical companion…

Sunday, October 12, 2008 – Today in 1891, the Astronomical Society of France was established. Exactly one year later in 1892, astronomy great E. E. Barnard was hard at work using the new tool of photography and became the first to discover a comet – 1892 V – in this way! But Barnard’s main photographic interest was in capturing details of the Milky Way. Just as soon as skies are dark again, we’ll have a look at more of Barnard’s work.

Do you like looking at things which are considered dubious? Then tonight let’s start on the lunar surface and peek at a ray system whose origins are uncertain. You’ll find the bright ring of Bessel almost in the center of Mare Serenitatis, but the ray system is splashed all over it. Did they come from Menelaus on the mare’s edge? Or from as far south as Tycho? Next time the terminator passes over this region, look closely. Do you see the rays now – or just a complicated system of dorsa?

With tonight’s bright skies, it will be difficult to practice any astronomy – or will it? Try re-locating Fomalhaut and drop about a handspan south-southwest into Grus to pick up bright star Beta (RA 22 42 40 Dec -46 53 04).

Around 170 light-years from Planet Earth, Beta is the 59th brightest star in the sky and the second brightest star not to have a proper name. It’s an M-type supergiant, but one that is also slightly irregular – changing by about a third of a magnitude in approximately 37 days. Well evolved, Beta is on its way to becoming a Mira type and is only the size of the orbit of Venus. Its loss of mass could mean it has a dead carbon-oxygen core, and studies at infrared wavelengths point to a shell waiting to be expelled.

In the telescope, you will see Beta also has a visual companion to the south. Although it is unrelated to Beta itself, modern interferometry suggests there may be a true companion star which has yet to be resolved. No matter how you view it, you’ll like Beta for its rich color! Remember its position…

Unitl next weekend and darker skies, have a wonderful journey!

This week’s awesome images are: Apollo 16 image of Letronne – Credit: NASA, Zeta Capricorni – Credit: Palomar Observatory, courtesy of Caltech, Schickard region – Credit: Oliver Pettenpaul, Fomalhaut – Credit: Palomar Observatory, courtesy of Caltech, Bessel Rays – Credit: David Richards and Beta Gruis – Credit: Palomar Observatory, courtesy of Caltech. Thank you so much! Seeing these photographs contributes so much to our understanding of both history and what we’re seeing!

Posted on by Tammy Plotner

How Many Moons Does Jupiter Have?

Io Transit by Paul Haese

When it comes to the mighty Jupiter – and seeing Jupiter’s moons through a small telescope or binoculars – timing is everything. Jupiter’s satellites are constantly on the move, and almost any time you observe you’ll see at least one. The four largest of Jupiter’s moons are known as the Galileans, and go by the names of Europa, Callisto, Ganymede and Io. But which one is which and how do you know what you’re looking at?

Thanks to some very cool tools like Sky & Telescope’s Jupiter’s Moon you can tell exactly what time a Jovian event is about to happen and observe it yourself. For example:

Saturday, May 17, 2008

17:36 UT, Io’s shadow begins to cross Jupiter.
18:42 UT, Io begins transit of Jupiter.
19:54 UT, Io’s shadow leaves Jupiter’s disk.
21:00 UT, Io ends transit of Jupiter.

Io Transit by Paul Haese

What transpires will look very much like this awesome photo done by Paul Haese. Jupiter Transit events are easy to observe even with a small telescope, but it does require some techniques. First of all, you cannot simply glance in the eyepiece and see it happening with ease. It does require higher magnification and patience! The trick is to get comfortable and just watch… During your extended observing session, moments of stability will come and go and it won’t take long before you notice a phenomena that recurs. The body of Jupiter’s moons are a little more difficult to spot, but the shadow becomes very easy when you take your time and really look!

So what happens if your equipment or skies aren’t up to the task? Never fear… You’re not left out of the game. Timing is everything. Begin by observing Jupiter well in advance of the event and take note of the Galilean moon’s position. By checking every few minutes or so, you will notice when one is about to go into transit because you’ll see it near Jupiter’s limb. Keep watching… Because it will simply disappear! (This is also a great clue for larger telescopes to understand where to look and where the shadow will appear.)

While viewing through the average telescope isn’t going to be as good as what can be seen photographically, just timing and participating in an event is a wonderful opportunity to expand your astronomy knowledge and experience. Watching a Galilean moon transit Jupiter, or Jupiter’s Red Spot is something which can be done from light polluted skies and doesn’t require a lot of technical skills – just patience. Mark your calendars for 3:50 Universal Time on May 22nd when Jupiter will appear to have no moons at all! Try following the event in advance of the predicted time and report what happens. So how many moons does Jupiter have? The real answer is 63. But the question should be…

How many can you see?

This incredible image of an Io transit was done by Paul Haese, a member of MRO, using a Peltier cooled C14 and Skynyx 2-0 monochrome camera with RGB Astronomik filters. Paul’s planetary imaging skills are legendary. The UK has Damien Peach, the US has Don Parker and AU has Paul Haese! Thank you so much for sharing…

Posted on by Tammy Plotner

How To Use A Telescope

Choose Your Observing Site To Use A Telescope

One of the most important things to begin with is to carefully choose the site you will use set up and use your telescope at. While it would be tempting to take your new telescope out of the box and use it that night, it’s best to wait just a day or two! Begin the first clear night by going outside a taking a good look around. You want to choose an observing site where the view is as unobstructed and as dark as possible. While you are doing this, keep in mind that it must be comfortable to you as well. While the vista might be far improved a kilometer away – do you really want to have to take your equipment that distance each time you want to use it? Look at many different alternatives. If you live in a city, perhaps a rooftop will serve well. Urban settings often have very suitable yards that will work for most observing projects and rural settings are ideal.

Light pollution is another factor when choosing your site. Again, keep in mind that you must have a site that is accessible to enjoy. It isn’t always possible if you live in a well-lit area to take your equipment remote each time you want to use your telescope – but a sheltered area, such as in the shadow of a house, often blocks stray light well enough to enjoy using your telescope right at home. Of course, finding a dark sky site is also important, too. But not half as much as just finding a spot that you will enjoy and use.

While out during the day, look for level, solid ground. No one wants to see their telescope take a tumble. While it is tempting to set up on a deck, remember that any footsteps will cause vibration in the image. Setting up on places like a blacktop driveway or concrete can also cause thermal issues, too. Avoid them when you can, but do not discard these types of sites if they are comfortable and accessible.

How To Set Up Your Telescope

While every telescope set-up is slightly different, they are all basically the same in some respects. There must be an optical tube of some type, a mount and eyepieces. Take the time to become familiar with all the components of your telescope! If you must assemble and dis-assemble your telescope each time you use it, it’s a very wise idea to practice a few times before you go out in the dark. There is simply nothing more frustrating that trying to learn to set up your equipment when you cannot see what you are doing – or to loose a small part in the dark. If it is at all possible, leave your telescope and tripod fully assembled and in a place where it is easy to set outside at a moment’s notice. You’ll find that you’ll use it far more often if it takes less work.

Your telescope’s view is also dependent on ambient temperature. If you wear eyeglasses, you understand why! If you go from a very cool environment, such as a air-conditioned house, into a humid outdoors setting, your glasses fog up, don’t they? And so will your telescope’s optics. The same is true when observing outdoors in the winter. When taking your telescope from a heated climate to a cold one, you must give the telescope time to “cool down”. Even just a few degrees can mean waiver in the image.

Align your finderscope in advance! While this sounds rather strange, another frustrating thing to do in the dark is to align a finderscope – especially on a moving target. Once you have learned to assembly your telescope, learn to align your finder. Set up your scope and aim at a distant object. Now align your finder to that object as well. This will make things much easier, later!

Once your telescope is set up, the last thing to remember is to stow your things neatly so you won’t have any problems finding them when it comes time to put things away. Dust covers and eyepieces cases are so easy to lose. Keep things neat and you won’t have any problems. Choose the eyepiece you think you will need in advance and have them in a place where you won’t need to fumble in the dark. Have your red flashlight and maps handy. These are just little things that make using your telescope much more enjoyable!

Choose Your Observing Times

Experience will become your best teacher. It won’t take long before you realize that very humid nights or exceptionally cold ones are not particularly good times to observe. Unless you plan on looking at the Moon itself, nights that are well moon-lit are also not good times to search for a faint galaxy, either. Little things, like waiting for a planet to clear the atmospheric “murk” at the lower horizon mean a much better viewing experience.

How To Use A Telescope

Now that you have your observing site, learned to set up, and established a time to practice astronomy… Let’s learn how to use your telescope!

If you have an equatorial mount, align the axis to the pole star. Altazimuth mounts do not need this step. Take off your dustcaps and stow them away. Double check to make sure your tripod legs are secure. Choose your low power eyepiece and put it in the focuser. Are you ready? Now, loosen the axis and take aim at a star using your finderscope. When the star is aligned in the center of the finder, tighten the axis and it’s time to go to the eyepiece. Gently adjust the focus in or out until you have a crisp, clean image. Now watch the star move. This direction is always west – regardless of the orientation in the eyepiece. For equatorial mounts, use your slow motion cables to learn to “track” the star. For altazimuth mounts, use the pan control or shift the tube manually (dobsonian models). Once you have learned to “follow” and object, it’s time to star hop!

Each time you go to a new object with an equatorial mount, you must unlock the axis. The same is true with some styles of altazimuth mounts. Once you have the general location in the finder, lock the axis back up and use the slow motion cable controls or panhandle control to make small moves. Using a low power eyepiece first will help you locate things much easier, and you can then switch to more magnification once the object is located.

When you are finished for the evening, make sure to replace all your dustcaps. If your optics should become dewed, don’t wipe them off. Allow them to air dry to avoid micro-scratches on delicate coatings. Always make sure to give your observing area one last check before leaving just in case you’ve forgotten something!

Posted on by Tammy Plotner

A Herschel Anniversary – NGC 891 by Ken Crawford

NGC891 by Ken Crawford

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On this night – October 6 – in 1784, Sir William Herschel was busy at the eyepiece of his telescope with a new galaxy he’d just discovered. It was a beauty, too. A pencil-slim, edge-on galaxy with a dark dust lane. Herschel marked it down in his fifth catalog as discovery 19, but when he got excited talking about his sister Caroline’s discoveries, he made a mistake. Let’s learn…

Even though William Herschel later confused NGC 891 with Caroline’s independent discovery of NGC 205 (M110), you can understand how the brother/sister astronomy team could honestly make a mistake. In the words of Caroline Herschel; “I knew too little of the real heavens to be able to point out every object so as to find it again without losing too much time by consulting the Atlas. But all these troubles were removed when I knew my brother to be at no great distance making observations with his various instruments on double stars, planets, etc., and I could have his assistance immediately when I found a nebula, or cluster of stars, of which I intended to give a catalogue; but at the end of 1783 I had only marked fourteen, when my sweeping was interrupted by being employed to write down my brother’s observations with the twenty-foot.”

Oddly enough, Herschel’s mistake was perpetuated by Admiral William Henry Smyth – who when he retired from the Royal Navy spent his time in his private observatory equipped with a 6-inch refractor. There he observed a variety of deep sky objects, including double stars, clusters and nebulae, and kept careful records of his observations, publishing his work as the “Cycle of Celestial Objects” – including Herschel’s mistake. But in the end, does it really matter which Herschel discovered it? It’s what’s out there that counts…

Located some thirty million light years away in the Local Super Cluster, NGC 891 is wrapped by a cold, gaseous halo. According to Tom Oosterloo (et al); “HI observations are among the deepest ever performed on an external galaxy. They reveal a huge gaseous halo, much more extended than seen previously and containing almost 30 % of the HI. This HI halo shows structures on various scales. On one side, there is a filament extending (in projection) up to 22 kpc vertically from the disk. Small halo clouds, some with forbidden (apparently counter-rotating) velocities, are also detected. The overall kinematics of the halo gas is characterized by differential rotation lagging with respect to that of the disk. The lag, more pronounced at small radii, increases with height from the plane. There is evidence that a significant fraction of the halo is due to a galactic fountain. Accretion from intergalactic space may also play a role in building up the halo and providing low angular momentum material needed to account for the observed rotation lag. The long HI filament and the counter-rotating clouds may be direct evidence of such accretion.”

Accretion? Accretion from where? Is NGC 891 gathering material from somewhere else? Apparently so. According to work of Mapelli (et al): “It has been known for a long time that a large fraction of disc galaxies are lopsided. We simulate three different mechanisms that can induce lopsidedness: flyby interactions, gas accretion from cosmological filaments and ram pressure from the intergalactic medium. Comparing the morphologies, HI spectrum, kinematics and m = 1 Fourier components, we find that all of these mechanisms can induce lopsidedness in galaxies, although in different degrees and with observable consequences. The time-scale over which lopsidedness persists suggests that flybys can contribute to ~20 per cent of lopsided galaxies. We focus our detailed comparison on the case of NGC 891, a lopsided, edge-on galaxy with a nearby companion (UGC 1807). We find that the main properties of NGC 891 (morphology, HI spectrum, rotation curve, existence of a gaseous filament pointing towards UGC 1807) favour a flyby event for the origin of lopsidedness in this galaxy.”

Ah, ha! So, we have a nearby companion galaxy. We’ve learned recently that combining galaxies produces starburst activity and the case is true of NGC 891 as well. Studies done as recently as June 2008 indicate starbust activity based on the strength of the polycyclic aromatic hydrocarbon (PAH) features. And where are those PAHs? Why, in the halo, of course. According to the work of Rand (et al): “We present infrared spectroscopy from the Spitzer Space Telescope at one disk position and two positions at a height of 1 kpc from the disk in the edge-on spiral NGC 891, with the primary goal of studying halo ionization. Our main result is that the [Ne III]/[Ne II] ratio, which provides a measure of the hardness of the ionizing spectrum free from the major problems plaguing optical line ratios, is enhanced in the extraplanar pointings relative to the disk pointing. Using a 2D Monte Carlo-based photoionization code that accounts for the effects of radiation field hardening, we find that this trend cannot be reproduced by any plausible photoionization model and that a secondary source of ionization must therefore operate in gaseous halos. We also present the first spectroscopic detections of extraplanar PAH features in an external normal galaxy. If they are in an exponential layer, very rough emission scale heights of 330-530 pc are implied for the various features. Extinction may be non-negligible in the midplane and reduce these scale heights significantly. There is little significant variation in the relative emission from the various features between disk and extraplanar environment. Only the 17.4 ?m feature is significantly enhanced in the extraplanar gas compared to the other features, possibly indicating a preference for larger PAHs in the halo.”

So where is all this going? Current research shows a correlation between PAH abundance with galactic age. When asymptotic giant branch cough their carbon dust back into the interstellar medium at the end of their evolution, they become the primary source of PAHS and carbon dust in galaxies. As we know, a galaxy is one big recycling plant, and the ejecta is returned back to the interstellar medium after a few hundred million years along the line of main sequence evolution. But, the filamentary pattern extending away from the galactic disc of NGC 891 may very well point to stellar supernova explosions. By contrast, those, huge, massive stars that end up as Type II supernovae are the ones that blast dust and metals everywhere the moment they form.

So is this the result of old – or new – activity? According to Popescu (et al): “We describe a new tool for the analysis of the UV to the sub-millimeter (sub-mm) spectral energy distribution (SED) of spiral galaxies. We use a consistent treatment of grain heating and emission, solve the radiation transfer problem for a finite disk and bulge, and self-consistently calculate the stochastic heating of grains placed in the resulting radiation field. We use this tool to analyse the well-studied nearby edge-on spiral galaxy NGC 891. First we investigate whether the old stellar population in NGC 891, along with a reasonable assumption about the young stellar population, can account for the heating of the dust and the observed far-infrared and sub-mm emission. The dust distribution is taken from the model of Xilouris et al. (1999), who used only optical and near-infrared observations to determine it. We have found that such a simple model cannot reproduce the SED of NGC 891, especially in the sub-mm range. It underestimates by a factor of 2-4 the observed sub-mm flux. A number of possible explanations exist for the missing sub-mm flux. We investigate a few of them and demonstrate that one can reproduce the observed SED in the far-infrared and the sub-mm quite well, as well as the observed radial profile at 850 mu m. For the models calculated we give the relative proportion of the dust radiation powered by the old and young stellar populations as a function of FIR/sub-mm wavelength. In all models we find that the dust is predominantly heated by the young stellar population.”

Although it may have been busy at one time, NGC 891 is quiet now. According to Rowan Temple, “Using a sample of other local galaxies, we compare the X-ray and infrared properties of NGC 891 with those of `normal’ and starburst spiral galaxies, and conclude that NGC 891 is most likely a starburst galaxy in a quiescent state.” So take a look when you have time. This magnitude 10 beauty is located at (RA 2 : 22.6 Dec +42 : 21) at is often considered to be one of the finest deep sky objects Messier never cataloged.

No matter which Herchel discovered it.

Many thanks to AORAIA member Ken Crawford for the use of his superb image!