Category: Guide to Space

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Measuring the rotation of Saturn is actually a more complicated job than you might think. That’s because Saturn is just a ball of hydrogen and helium, without any solid surface features that you can measure from day to day. Saturn’s rotation is even more complicated than that, since different parts of the planet rotate at different speeds. So asking what the rotation of Saturn is depends on which part of the planet you’re talking about.

The visible features of Saturn rotate at different rates depending on their latitude (distance from the equator). Astronomers have developed three different systems for measuring the rotational speed of Saturn. System I is for regions around the planet’s equator. The System I rotation speed is 10 hours and 14 minutes. Above and below the Equatorial Belt is called System II. Here the rotation speed is 10 hours and 39 minutes.

System III is based on the rotation of Saturn’s magnetic field, and was measured by NASA’s voyager spacecraft. They determined that Saturn’s magnetic field takes 10 hours and 39 minutes to complete a rotation. But here’s a strange mystery. The rotation of the magnetic field was measured again by NASA’s Cassini spacecraft in 2004, and it found that the rotation of the magnetic field had slowed down to 10 hours and 45 minutes. So it appears that the rotation of Saturn can change over time.

We have written many articles about Saturn for Universe Today. Here’s an article that goes into much more detail about the process of measuring a day on Saturn.

Want more information on Saturn? Here’s a link to Hubblesite’s News Releases about Saturn, and here’s NASA’s Solar System Exploration Guide.

We have recorded a podcast just about Saturn for Astronomy Cast. Click here and listen to Episode 59: Saturn.

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Saturn is the second largest planet in the Solar System (after Jupiter), but you really need a comparison. Let’s take a look at Saturn compared to Earth.

First, let’s just look at Saturn’s physical characteristics. The equatorial diameter of Saturn is 120,536 km; that’s about 9.5 times bigger than the diameter of the Earth. The surface area of Saturn is 83 times the area of Earth, and the volume is 764 times the volume of Earth. In other words, you could fit 764 planets the size of Earth inside Saturn. Finally, the mass of Saturn is 95 times the mass of the Earth.

One interesting comparison between Earth and Saturn is density. Earth is the densest planet in the Solar System, while Saturn is the least dense. The density of Earth is 5.52 g/cm³, while the density of Saturn is 0.687 g/cm³. In other words, Earth is 8 times as dense as Saturn.

Another region where Saturn and Earth are similar is gravity. Of course, Saturn has much more mass than Earth, but it’s spread out over a larger area. Saturn doesn’t have a solid surface, of course, but if you could walk on the surface of Saturn, you would experience almost exactly the same gravity as you feel on Earth.

Earth takes 24 hours to complete a day, while Saturn takes 10 hours and 32 minutes. A year on Earth is, well, 1 year, while a year on Saturn lasts 30 years.

Are you wondering about other planets compared to Earth? Here’s an article about Jupiter compared to Earth, and here’s Mars compared to Earth.

Want more information on Saturn? Here’s a link to Hubblesite’s News Releases about Saturn, and here’s NASA’s Solar System Exploration Guide.

We have recorded a podcast just about Saturn for Astronomy Cast. Click here and listen to Episode 59: Saturn.

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The constellation of Vela is located south of the ecliptic plane and was once part of the much larger constellation of Argo Navis – now divided into three parts. It is now abbreviated and Vela represents the “sails”. Vela encompasses 500 square degrees of sky, ranking 32nd in constellation size. It has 5 main stars in its asterism and 50 Bayer Flamsteed designated stars within its confines. Vela is bordered by the constellations of Antlia, Pyxis, Puppis, Carina and Centaurus. It is visible to all observers located at latitudes between +30° and ?90° and is best seen at culmination during the month of March.

There are three annual meteor showers associated with Vela. The first is the Gamma Velids which peak on or about the night of January 6/7 of each year. At maximum, this stream produces about 8 meteors per hour average. The second is the Delta Velids, which peak on or about February 15 of each year. This is a weak stream with the radiant near Delta and viewers can expect to only see about one meteor per hour on the average. The last is the Puppid-Velid meteor shower, which begins activity on or about December 1 and lasts through around December 15 of each year. The expected date of maximum activity usually occurs on or about December 6 and the complex meteoroid stream can produce up to 10 faint meteors per hour on the average. Most Puppid-Velid meteors are quite faint, but occasionally produce bright fireballs. This particular shower is best viewed just before dawn.

While Vela has no real mythology associate with it since it wasn’t visible to the ancient Greeks and Romans, it does have some very lovely tales and a fascinating history. Argo Navis (or simply Argo) was a large southern constellation representing the Argo, the ship used by Jason and the Argonauts in Greek mythology. The Argo was built by the shipwright Argus, and its crew were specially protected by the goddess Hera. The best source for the myth is the Argonautica by Apollonius Rhodius. According to a variety of sources of the legend, the Argo was said to have been planned or constructed with the help of Athena. According to other legends it contained in its prow a magical piece of timber from the sacred forest of Dodona, which could speak and render prophecies. After the successful journey, the Argo was consecrated to Poseidon in the Isthmus of Corinth. It was then translated into the sky and turned into the constellation of Argo Navis. The name “Vela” is Latin for the sails of a ship!

Now, let us set sail on a binocular tour of Vela as we begin with its largest object, the Vela Supernova Remnant. Located some 800 light years away from Earth and formed about 11,000-12,300 years ago, this shredded curtain of interstellar medium is the result of a gigantic explosion of a star in a supernova – and explosion so massive it covers a full 8 degrees of sky! When it comes to this area, though, the spherical, expanding shock wave is most visible only in X-rays – but don’t stop scanning around. Spanning over distance of 100 light years of space, you’ll find threads of nebulosity, filamentary structure and gigantic shock formations in visible light, too.

Take a look with your binoculars on the northern edge for open cluster Trumpler 10 (RA 08: 47 42 Dec -42: 27 00). Chances are this magnitude 4, widely scattered stellar beauty was first discovered by Nicholas Lacaille in 1751 when he was first cataloging the southern skies. At around 47 million years old and about 1100 light-years distant, this region has been studied for galactic fountains and their connection with high and intermediate velocity clouds, as well as isolated cooling neutron stars and blue straggler stars in open star clusters!

Further along the Vela Supernove Remnant on the central eastern edge is galactic star cluster NGC 2659 (RA 8 : 42.6 Dec -44 : 57). This magnitude 8, Astronomical League’s Southern Sky Binocular Challenge is a nice compression of stars to large binoculars and well resolved to a small telescope. The brightest members of NGC 2659 are unevolved B and A0 stars, and the cluster may also contain an A0 giant star.

Now turn your attention to Delta Velorum – the “8” symbol on our chart. Delta is the second brightest star here and the brightest star in the night sky that doesn’t have a proper name. Located about 80 light years from our solar system, Delta is a system of its own. That’s right… a multiple star system! This class A1 dwarf is at least triple star, and may be quintuple. Both the A and B stars are easily separated in a telescope – and the A (primary) star is also a spectroscopic binary star. Look about an arc minute away for two more – a pair of faint, disparate red dwarf stars.

Get your binoculars back out and hop north for the huge, open galactic star cluster IC 2391 (RA 8 : 40.2 Dec -53 : 04). Also known as the “Omicron Velorum Cluster”, this magnitude 2.5 stellar jewel box was first described by Al Sufi about 964 AD while Louis de Lacaille found it independently on February 11, 1752. Containing about 30 or so stars which are easily resolved in a telescope, this treat is also on the Astronomical League’s Southern Sky Binocular Club list as well as being a Caldwell object, too.

Keeping to a low power, wide field view – such as small binoculars or a rich field telescope, will help you to spot nearby open star cluster NGC 2669 (RA 8 : 44.9 Dec -52 : 58), too. At magnitude 6, this area will stand out as a small compression of the starfield that isn’t quite as interesting as its splashy neighbor, but it is on the AL Southern Sky Telescopic Club challenge list. Be sure to take a look, because it has been highly studied for proper motions.

Keep binoculars handy to split optical double star Gamma 1 and Gamma 2. The dimmer of the pair – Gamma 1 – is named Suhail, and is jokingly referred to as Regor. Is it special? You bet. Because it has some very unusual pattern in its stellar spectral signature, Suhail is also known as the “Spectral Gem of Southern Skies” because it contains bright emission lines instead of dark absorption lines. But don’t stop with just binoculars – use a telescope, too! Brighter Gamma 2 is actually a spectroscopic binary star composed of a blue supergiant and the heaviest known, massive Wolf-Rayet star discovered to date. The binary companion is a blue-white B-type subgiant star which can be separated from the Wolf-Rayet binary easily with binoculars!

Let’s head south for star cluster NGC 2547 (RA 8 : 10.7 Dec -49 : 16). This magnitude 4.7 gathering of stars spans a handsome 20 arc minutes and was discovered by Abbe Lacaille in 1751. Also known as Dunlop 410, Melotte 84 and Collinder 177, the area has been the target of the Spitzer Space Telescope for some very interesting things – like M dwarf debris disk candidates! According to research done by Jan Forbrich (et al): “With only six known examples, M-dwarf debris disks are rare, even though M dwarfs constitute the majority of stars in the Galaxy. After finding a new M dwarf debris disk in a shallow mid-infrared observation of NGC 2547, we present a considerably deeper Spitzer-MIPS image of the region, with a maximum exposure time of 15 minutes per pixel. Among sources selected from a previously published membership list, we identify nine new M dwarfs with excess emission at 24 micron tracing warm material close to the snow line of these stars, at orbital radii of less than 1 AU. We argue that these are likely debris disks, suggesting that planet formation is under way in these systems. Interestingly, the estimated excess fraction of M stars appears to be higher than that of G and K stars in our sample.” Wow… An open cluster that might have planet candidates in it!

Now, star hop north for galactic cluster NGC 2670 (RA 8 : 45.5 Dec -48 : 47). Near magnitude 8, this UFO-shaped configuration of stars is part of the Astronomical League’s Southern Sky Binocular Club and Deep Sky binocular observing list. It has been well studied for mass loss of its stars in the red giant star stage and will appear as a thin streak in small aperture.

Head northeast for open star cluster NGC 2910 (RA 9 : 30.4 Dec -52 : 54). This magnitude 7 beauty is also a Astronomical League’s Southern Sky Binocular Club object and part of the Deep Sky binocular observing list. It was discovered by John Herschel on April 10, 1834 and has been the target for study for triggered star formation.

Let’s go to the telescope to study globular cluster NGC 3201 (RA 10 : 17.6 Dec -46 : 25). Discovered by James Dunlop on May 28, 1826, this magnitude 7 globular is easy for a telescope of any size, and larger aperture will fully resolve the loose structure on this one. Known as a low galactic latitude globular cluster, the population of stars isn’t very high – and it was fully resolved by the Hubble Space Telescope!

Keep the telescope out as we hop north for galaxy NGC 3256 (RA 10 : 27.8 Dec -43 : 54). At magnitude 11 and spanning 3 arc minutes – this is one impressive little peculiar galaxy. NGC 3256 belongs to the Hydra-Centaurus galaxy supercluster complex – but what you see here is the remains of a galaxy collision that occurred long ago. In our backyard telescopes, we can see two distinct nucleus regions, but the Hubble Space Telescope was able to resolve out intricate filaments of dark dust, unusual tidal tails of stars – the result of a huge, galaxy interaction that’s still occurring!

Last, but not least, let’s make run for the border… the Antila border! Our target is NGC 3132 (RA 10 : 07.0 Dec -40 : 26), better known as the “Eightburst Planetary” or “Southern Ring Nebula”. At magnitude 8 you can make out planetary nebula signature with binoculars, but you’ll need at least a mid-sized telescope to begin to see any details. Only slightly larger than Jupiter in apparent size in the eyepiece, the Eightburst resides about 2,000 light years from our Sun and contains two central stars – one of 10th magnitude, the other 16th. Yep. A planetary nebula formed from a binary star! So who is responsible for the nebula shell we’re seeing? The fainter, white dwarf star. It is now smaller than our own Sun, but extremely hot – its flood of ultraviolet radiation igniting the region in the ghostly glow we can see!

Sources:
Wikipedia
SEDS
Chandra Observatory
Chart courtesy of Your Sky.

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The northern circumpolar constellation of Ursa Minor was one of the 48 original constellations listed by Ptolemy, and remains one of the 88 modern constellations recognized by the IAU. Ursa Minor is currently the location of the north celestial pole, yet in several centuries, due the precession of the equinoxes, it will change. Ursa Minor covers 256 square degrees of sky and ranks 56th in size. It contains 7 main stars in its asterism and has 23 Bayer Flamsteed designated stars within its confines. Ursa Minor is bordered by the constellations of Draco, Camelopardalis and Cepheus. It is visible to all observers located at latitudes between +90° and ?10° and is best seen at culmination during the month of June.

There is one annual meter shower associated with Ursa Minor called the Ursids. Beginning on or about December 17th of each year, we encounter the meteoroid stream and activity can last through the end of December. The meteor shower itself is believed to be associated with Comet Tuttle and was probably discovered by William F. Denning during the 20th century. The peak date of activity occurs on December 22 during about a 12 hour window and you can expect to see about 10 meteors per hour on the average from a dark sky location.

In mythology, Ursa Minor is meant to represent a baby bear with a very long tail. Perhaps this springs from the “tale” of Kallisto and her son, who were placed in the sky as a bear and son. The tail is believed to be elongated from have been swung around the north star! In some forms of mythology, the seven stars of the Little Dipper were considered to be the Hesperides, daughters of Atlas… and it forms the “dragon’s wing” in yet other stories. While the “Little Dipper” asterism is a bit more difficult to recognize because its stars are more faint, once you do understand the pattern, you’ll always remember it. How? The star at the end of the little dipper handle is Polaris, the North Star. Polaris is easily identified by drawing a mental line through the two stars which form the end of the “bowl” of the Big Dipper and extending that line five times the distance.

Now, let’s take a look at Ursa Minor! While there are only a very few deep space objects here (and they require a large telescope) that doesn’t mean the constellation isn’t interesting. One handy thing to note is the stars themselves. The four stars in the “bowl” of the little dipper are unusual because they are of second, third, fourth and fifth stellar magnitude. While that might not seem like a big deal, it’s a great way to judge your sky conditions. What is the dimmest of the stars that you can see? Beta (B) is 2, Gamma (Y) is 3, Zeta (the squiggle) is 4 and the unmarked corner is Eta (n) and it is stellar magnitude 5.

Ready for the brightest star? Then say hello to Alpha (a) – Polaris. Alpha Ursae Minoris is also known as the “North Star” and even as the Lodestar. While it might be 430 light-years from Earth, it is currently the closest star to the north celestial pole and a main sequence supergiant star. But don’t just glance at it and walk away… Get out your telescope! In 1780, Sir William Herschel noticed something a little strange when he was looking at Polaris, and so will you… it has a companion star. That’s right. Polaris is a binary star. Not only that… But when astronomers were examining Polaris B’s spectrum, they noticed something else… You got it! Polaris B also has a spectroscopic companion, making this a tertiary star system. Are you ready for more? Then get this… Polaris A is also a Cepheid variable star! While its changes are very small (about 0.15 of a magnitude every 3.97 days), Polaris has brightened by 15% since we first began studying it and its variability period has lengthened by about 8 seconds each year since. That makes Polaris more than just a another star… It’s a super star!

Now aim your binoculars at Beta Ursae Minoris. Its name is Kochab and it is about 127 light years from our solar system. This orange giant star shines about 130 times more brightly than our own Sun. Somewhere around 3000 years ago, Kochab was once the pole star – but as Earth’s precessional motion changed, so did its position. Even then it still wasn’t quite as close as Polaris!

How about Gamma Ursae Minoris? That’s the “Y” symbol on our chart. Known as Pherkad, this spectral class A3 star is about 480 light years away and it is pretty special, too. Why? Because it’s a Delta Scuti type variable star and its brightness varies by 0.05 magnitudes with a period of 3.43 hours. While you’re not going to notice any change by just watching, image the power behind a star that shines 1100 times more luminous than the Sun, and possesses a radius 15 times larger!

Are you ready for Epsilon? Then get out the telescope, because 347 light year distant Epsilon is an eclipsing spectroscopic binary star. (Say that five times fast!) It is classified as a yellow G-type giant star with a mean apparent stellar magnitude of 4.21. In addition to light changes due to eclipses, the system is also classified as an RS Canum Venaticorum type variable star and its brightness varies from magnitude 4.19 to 4.23 with a period of 39.48 days, which is also the orbital period of the binary. The binary it orbited by a third component, Epsilon Ursae Minoris B, which is an 11th magnitude star, 77 arc seconds distant.

Now for Delta – the “8”. Delta Ursae Minoris is about 183 light years away and goes by the strange name, Pherkard. While it isn’t as grand as its mates, at least it is a white A-type main sequence dwarf star!

Last, but not least, is RR Ursae Minoris. You’ve got it… The double letter designation denotes a variable star. While changes are very small (4.73 at minimum and magnitude 4.53 at maximum) it’s the period that counts here. The changes take period of 748.9 days to happen! This means that RR has been highly studied to make sure it doesn’t have a spectroscopic companion – and so far none have been found.

Sources:
SEDS
Wikipedia
University of Wisconsin
Chart courtesy of Your Sky.

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The northern circumpolar constellation of Ursa Major is perhaps one of the oldest and most recognized of all. Listed by Ptolemy as one of the original 48 constellations, it has played a role in all cultures and civilizations – even recorded in historic literature, such as the works of Homer, Spenser, Shakespeare and Tennyson. Ursa Major has been depicted by Vincent Van Gogh and mentioned in the Bible. Its primary asterism is formed by anywhere from 7 to 20 stars (depending on how many you wish to include) and it contains 93 Bayer Flamsteed designated stars within its borders. It covers an expansive 1280 degrees of sky, ranking third in size. Ursa Major is bordered by the constellations of Draco, Camelopardalis, Lynx, Leo Minor, Leo, Coma Berenices, Canes Venatici and Bootes. It is visible to all observers located at latitudes between +90° and ?30° and is best seen at culmination during the month of April.

According to Greek mythology, the god Zeus once desired a woman named Kallisto. Quite understandably, his wife Hera became jealous and turned Kallisto into a bear. In the meantime, Kallisto’s son, Artemis, almost shoots his mother by accident while hunting. In order to avert tragedy, Zeus turns them both into stars and sets them in the sky. Despite the Greek tale, a resounding amount of cultures also recognized this constellation as being a bear – including many native American Indian tribes, the Jewish culture and more. No matter if you can “see” the bear in the stars or not, the seven brightest stars of Ursa Major form the well-known asterism known as the “Big Dipper” (as it is called in the United States) or the Plough (as it is referred to in the United Kingdom and Ireland). The Big Dipper constellation also played a very important role in the Underground Railroad which helped slaves escape from the South before the Civil War. By connecting the stellar patterns, escapees could easily follow the stars north and there were songs quietly passed among the slave population which told of the “Drinking Gourd” and how to follow its light.

Before we begin our binocular tour, let’s start first with a visual tour – because this asterism of stars is very significant in its own right. With the exception of Alpha (Dubhe) and Eta (Alkaid), these bright stars are all part of a stellar association known as the Ursa Major Moving Group. This means all of these stars share the same proper motion – heading towards a common point in Sagittarius. As a collective – along with several other stars – the group is known as Collinder 285 and is roughly 80 light years away from Earth. The Ursa Major Moving Group was discovered in 1869 by Richard A. Proctor, and may once have been a part of a much larger open star cluster.

Now, turn your attention towards the star in the center of the handle of the Dipper – Zeta – the squiggle on our chart. If you can resolve this close set of stars with just your unaided vision, then you’d be riding a horse in the Arab army! Collectively this pair is known as Mizar and Alcor, the “Horse and Rider”… and splitting them visually was once used as an eyesight test. Take a look in binoculars to easily split this optical double star – and then take a closer look in a telescope! Mizar, the brighter of the two, is true binary star system. Both the primary star – and the 4th magnitude secondary star are also spectroscopic binary stars, too… making it a four star system located about 78 light-years away. While Mizar and Alcor aren’t gravitationally bound to each other, they still share common ground. Separated by only about 3 light years, this pair also shares proper motion and belongs to the Ursa Major Moving Group!

Before we move on to fainter objects, aim your binoculars between Epsilon and Delta to pick up Messier 40 (RA 12 : 22.4 Dec +58 : 05). This faint double star was found by Charles Messier while looking for a nebula that was incorrectly reported by Johann Hevelius. While we can never be quite sure of why Messier included this optical double star in his catalog, we can always include it on our observing list!

Next up? Another binocular object (and spectacular in any telescope!) as we head for M81 (RA 9 : 55.6 Dec +69 : 04) and M82 (RA 9 : 55.8 Dec +69 : 41). Discovered in December, 1774 by JE Bode at Berlin, these two deep sky favourites hold secrets between themselves. Photographed as early as March, 1899, this pair is central to a group of galaxies encompassing the northern circumpolar constellations of Ursa Major and Camelopardalis. Modern photos show the superb spiral structure of the M81. At some 36,000 light years in diameter, it is one of the densest known galaxies. One third of the mass is concentrated at the core! Its’ glow is the combined luminosity of twenty billion suns… Often mistaken in the small telescope for an edge-on spiral, M81’s neighbor – M82 – shows no sign of “swirling”. A true space “oddity”! The light from M82 journeying back to our eyes, is polarized. This galaxy probably contains a super-massive magnetic field. Not only is M82 polarized visually, it is also a powerful radio source. Within its’ broken structure lay huge masses of dust accompanied by the radiance of stars possessing unusual spectral qualities. These facts lead scientists to believe that a violent outburst may have occurred within the galaxy as recently as 1.5 million years ago… About the time when our own adventurous ancestral species, Homo Erectus, began seeking pattern in the Night Sky!

It is estimated M82’s defining event released the energy equivalent of several million exploding suns! “Shock waves” emanating from the galaxy greatly resemble synchrotron radiation. This phenomenon was first discovered in association with planetary nebula M1 – but within the M82, on an enormous scale! Can you image a super nova remnant the size of an entire galactic core region? Roughly every one hundred million years, M81 and M82 make a “pass” at one another. Immensely powerful gravitation arms reach out and intertwine to produce a spectacular embrace. It is theorized that during the last go-round, M82 raised rippling density waves which circulated throughout M81. The result? Possibly the most perfectly formed spiral galaxy in all of space! But M81’s influence left M82 a broken galaxy. Filled with exploded stars and colliding gas, a galaxy so violent it emits X-rays. Reactions induced by colliding dust and gas caused the birth of numerous brilliant stars. Stars capable of creating extremely dense atoms… Some of which are now excited by the kind of extreme motion that induces immense magnetic fields. The end may already be envisioned. Scientists speculate within a few billion years, out of the two, there shall be one. Two Cosmic Lovers locked in full embrace. Indistinguishable but for the welter of radiation only such an embrace can foment. It is known this same Danse Galactic awaits our own galaxy. Billions of years hence, our own galaxy and its’ largest neighbor – the Great Spiral in Andromeda – shall swoop together in consummation of their own Cosmic Courtship.

Let us not speak only of this fascinating galactic duet however. For the M81 and M82 also have some very unusual playmates! Neighboring galaxy NGC3077 displays some of the same “peculiarities” as its’ larger companion, M82. At 6,000 light years in diameter, NGC3077 is little more than a third the size of its protoype. Southwest of Spiral M81, is yet another “odd ball”. Like NGC3077, NGC2976 is a dwarf. At less than 1/5th the size of M81, NGC2976 is some 7,000 light years across. A value only thrice the distance between our own Sun and the nearby, spectacular Great Nebula in Orion! Three faint, irregular galaxies are also associated with our galactic pair. The NGC2366 jumps the border into Camelopardalis. IC2574 is found just a bit southeast of the M81 and is a real “toughie”! A smaller system known as Ho II was discovered in 1950 by astronomer E. Holmberg. Even farther into Camelopardis is the large spiral NGC2403, also thought to be a member of the M81/82 “family” of galaxies. As one of the two galaxy groups closest to our own “Milky Way” system (the other lies in Sculptor), this region presents a fascinating opportunity for study by the backyard astronomer. Why, the main pair can even be seen through 6x35mm binoculars!

Now it’s time to go to the telescope and head for Messier 97 (RA 11 : 14.8 Dec +55 : 01). Best known as the “Owl Nebula”, this 11th magnitude customer isn’t always the easiest thing to spot. Many observers cite M97 as one of the most difficult of the Messier studies to detect – especially through the kind of contrast-robbing skies found near larger cities. Pollution! The “Owl Nebula” gets its name for the vague gray-greenness of its light, and the two curious voids visible through larger scopes. These voids are thought to be the result of looking at a globe of nebulosity whose lowest-density poles lie at an oblique angle to our line of sight. The material making up planetary nebula M97 and the light causing it to glow are associated with a high surface temperature central star in the last stages of life. At the center of M97 is a faint 16th magnitude white dwarf star.

More? Then try Messier 109 (RA 11 : 57.6 Dec +53 : 23). At near magnitude 10, this barred spiral galaxy isn’t particularly easy for a small telescope, either. In the field with Gamma, M109 will show its faded central bar and prominent nucleus to the small scope, but requires large aperture and high magnification to make out structure. This object was observed by Pierre Mechain on March 12, 1781, and by Charles Messier on March 24, 1781 – but little did they know it is part of the Ursa Major Cloud – a huge group of galaxies in this area which our chart barely begins to list. M109 is about 55 million light years away from our solar system – but only as far as your backyard.

Ready for Messier 101 (RA 14 : 03.2 Dec +54 : 21)? While its apparent magnitude is brighter and it is larger, it is low surface brightness and less magnification is best. Located about three fingerwidths northeast of Mizar and Alcor, this near 8th magnitude galaxy was added as one of the last on the Messier list, but it ranks as one of the first to be identified as a spiral. While M101 is huge and bright, binoculars will only spot the bright central region – yet the average beginner’s scope (114mm) will begin to reveal arm structure with aversion. As aperture increases, so does detail, and some areas are so bright that Herschel assigned them their own catalog numbers. Even Halton Arp noted this one’s lopsided core as number 26 (“Spiral with One Heavy Arm”) on his peculiar galaxies list. At a distance of 27 million light-years, M101 might be somewhat disappointing to smaller scopes, but photographs show it as one of the most fantastic spirals in the Cosmos. Dubbed the “Pinwheel,” it heads up its own galactic group consisting of NGC 5474 to the south-southeast and NGC 5585 to the northeast, which are visible to larger scopes. It is estimated there may be as many as six more members as well! Be sure to take the time to really study this galaxy. The act of sketching often brings out hidden details and will enrich your observing experience.

Ready to try your hand at a few more obscure galaxy challenges? Then let’s rock! Our first will be 10th magnitude NGC 3945 (RA 11 : 53.2 Dec +60 : 41). This double barred spiral galaxy is bright and contains a terrific core region which just glows to large telescopes. No wonder it’s a Herschel 400 challenge! Now go for NGC 3359 (RA 10 : 46.6 Dec +63 : 13). Also 10th magnitude, beautiful barred spiral galaxy this is located 49 million light years away and recent studies have shown that the central bar has only formed within the the last 500 million years. Put in a high power eyepiece, this particular object shows great spiral galaxy structure! Ready for NGC 2685 (RA 8 : 55.6 Dec +58 : 44)? It’s a little fainter at magnitude 11, but it’s worth the hunt because it’s an is an unusual lenticular galaxy. It would make a great astrophotography expedition because it displays two axes of symmetry as well as an encircling ring composed of stars and interstellar matter. Leftovers from a tremendous galaxy interaction!

Ready to head into no man’s land for NGC 3583 (RA 11 : 14.2 Dec +48 : 19)? For a large telescope, you’ll find this 12th magnitude spiral galaxy oddly distorted despite what should be regular form. It is very low luminosity with an active galactic nucleus and a black hole! Now go to NGC 3675 (RA 11 : 26.1 Dec +43 : 35). At magnitude 11, this one makes a much better presentation with its bright core and even spiral galaxy structure. Look for a great oval that almost appears like an elliptical galaxy. More? Then try NGC 3319 (RA 10 : 39.2 Dec +41 : 41). Also magnitude 11, this 32 million light year distant spiral is going to look pencil-slim… edge-on! While it truly isn’t seen on the oblique, what we are witnessing is a very, very strong central bar and very, very faint spiral arms. Enjoy!As you can see from our chart, there are a HUGE amount of galaxies waiting to be discovered in Ursa Major! The area just northwest of Delta (the “8” symbol on our chart) is where the Hubble Space Telescope took its deep field image spanning an area 2.5 arc minutes across. To give yourself just a slight idea of how many galaxies there are in something that size, take a look at that image and then hold a grain of salt between your fingers at arm’s length against the starry backdrop near Delta. Can you see where no chart can even begin to list how many are there? Can you imagine how long an observing article would be even if you just told about the ones you could see with an average telescope?! Be sure to explore…

But, before we leave? Don’t forget about a very special star called Groombridge 1830. I’ve marked it on the chart as G1830 with an arrow. While it’s nothing more than a pretty ordinary yellowish class G8 subdwarf star, it’s what it is doing that’s extraordinary. Located just shy of 30 light years from us, Groombridge 1830 is a halo star – very old and metal-poor. Out of all the stars near our Sun, only 1 in every 10,000 can be like this one. Why? Because the daggone thing is standing still! When it was first discovered, it was believed to be THE star of the time with the highest proper motion. Reality check? Groombridge 1830 stands still while the rest of the Milky Way Galaxy rotates right on by.

Don’t let the “Bear” pass you by! Get your paws on a detailed star chart and enjoy everything is has to offer…

Sources:
Wikipedia
SEDS
Chandra Observatory
Chart Courtesy of Your Sky.

Saturn is a ball made up almost entirely of hydrogen and helium. The density and temperature changes the deeper into the planet you go, but Saturn can’t be said to have a solid surface. If you tried to walk on the surface of Saturn, you would fall into the planet, suffering higher temperatures and pressures until you were crushed inside the planet.

But Saturn appears to have a surface, so what are we looking at. The outer atmosphere of Saturn consists of 93% molecular hydrogen and the rest helium, with trace amounts of ammonia, acetylene, ethane, phosphine and methane. It’s these trace amounts that create the visible bands and clouds that we see in pictures of Saturn.

There are three main regions in Saturn’s troposphere – the part of the planet where weather is actually occurring. These three regions are completely defined by the temperature at which droplets condense into vapor and form clouds. The top visible cloud deck is made up of ammonia clouds and is found about 100 km below the top of the troposphere, in a region called the tropopause. Below that is a second cloud deck of ammonium hydrosulphide clouds. And below that, where temperatures are 0-degrees C, there are clouds of water.

Of course you can’t stand on the surface of Saturn, but if you could, you would experience about 91% of Earth’s gravity. In other words, if your bathroom scale says 100 kg on Earth, it would only say 91 kg on Saturn.

We have written many articles about Saturn for Universe Today. Here’s an article about patterns in Saturn’s atmosphere, and here’s a nice picture of Saturn’s clouds in silhouette.

Want more information on Saturn? Here’s a link to Hubblesite’s News Releases about Saturn, and here’s NASA’s Solar System Exploration Guide.

We have recorded a podcast just about Saturn for Astronomy Cast. Click here and listen to Episode 59: Saturn.

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The southern constellation of Tucana was first introduced in 1589 by Petrus Plancius on a celestial globe which was later added to Johann Bayer’s atlas – Uranometria – in 1603. Located south of the celestial equator, Tucana spans 295 degrees of sky and ranks 48th in size. It has 3 main stars in its asterism and contains 17 Bayer Flamsteed designated stars within its confines. It is bordered by the constellations of Grus, Indus, Octans, Hydrus, Eridanus and Phoenix. Tucana is visible to all observers located at latitudes between +25° and ?90° and is best seen at culmination during the month of November.

Since Triangulum Australe is considered a “new” constellation, there is no mythology associated with it – only how its name came to be. During the late 1600s Dutch navigators Pieter Dirkszoon Keyser and Frederick de Houtman were exploring the southern hemisphere and part of their work dealt with charting the southern stars as well. Petrus Plancius, a celestial cartographer included their observations on his celestial globe, as well as their constellation names which depicted the strange creatures which they encountered on their travels. At the time it was called “Den Indiaenschen Exster”, but Plancius changed it to “Toucan”. When Johann Bayer added the constellation to Uranometria, he included it as “Tucana” and it was later adopted permanently under this name by the International Astronomical Union.

Let’s begin our binocular tour with Alpha Tucanae – the “a” symbol on our chart. Alpha is a very interesting star not just because it is a binary star, but because it is an astrometric binary star. This means Alpha’s companion has never been directly observed, either optically or spectrally, but is believed to be there because of changes in the proper motion of the primary. What happens? Every 11.5 years we pick up a precise wobble from this 199 light year distant star!

Now, turn your telescope towards Beta Tucanae – the “B” symbol. Beta Tucanae is pretty special, too. Not just because it is a binary star – but because it is a whole, six-part star system. Located about 140 light years from Earth, the Beta system consists of Beta-1 Tucanae and Beta-2 Tucanae, the two brightest stars you will see in the eyepiece. Both main sequence dwarf stars, separated by about 27 arc seconds and very close to the same magnitude. Do you see a slight color difference? Beta 1 is a blue-white B-type star while Beta 2 is a white A-type star.

Time to turn up the magnification because both of these bright stars have at least one closer main sequence companion. Located 2.4 arcseconds away from Beta 1 is the A component. At magnitude 13.5, it will require a large telescope, but what fun! Now, look at Beta 2… approximately 0.38 arcseconds you’ll find the 6th magnitude D star! Ready for more? Then move on to Beta-3 Tucanae – another binary star which is separated from Beta-1 and Beta-2 Tucanae by 9 arc minutes. Both components of the binary system are white A-type main sequence dwarfs and it’s tight.. only 0.1 separation and nearly matching in magnitude. That means two stars which orbit each other only four Earth distances apart!

For the eye, binoculars or telescope, it’s time to have a look at NGC 104 (RA 0 : 24.1 Dec -72 : 05), better known as “47 Tucanae”. With a magnitude of 4 and spanning 31 arc minutes in size, this globular cluster will blow you away! Those huge, gravitationally bound balls of stars know as globular clusters aren’t without a heart. Containing a thick concentration of 10,000 to more than a million stars in a region spanning just 10 to 30 light-years, globular clusters are more akin to seething masses of suns where the lightweights head for the outer edges while the giants collect in the core. What causes this process? Do globular clusters really have a way of getting some stars closer to the heart? What you see in 47 Tucanae, is the second largest globular cluster in the Milky Way’s busy galactic halo. As its name “47 Tucanae” implies, its core was first cataloged as a star and numbered the 47th in Tucana the Toucan – but not for long. On September 14, 1751 a French astronomer named Nicholas Louis de Lacaille was the first to discover its true nature with a half inch diameter spy glass and cataloged it as nebulous object. Next to observe and catalog it were James Dunlop in 1826, and John Herschel in 1834 when it became New General Catalog (NGC) 104. At home some 13,400 to 16,000 light years away from our solar system, this inconceivably dense concentration of at least a million stars spans 120 light years at the outside, yet at its heart is more than 15,000 individual stars that are packed so densely that you couldn’t fit our solar system between them.

Believed to have all been born about the same time from the same cloud of gas, globular clusters like 47 Tucanae are a wonderful study of how stars evolve and interact. With such busy conditions, it only stands to reason that stellar collisions have occurred at one time or another and 47 Tucanae is no exception. In the core, 23 unusually hot and bright stars called blue stragglers have been identified – the double massive result of two stars bumping into one another. Due to the associated gravitational pull, heavier stars slow down and sink to the cluster’s core, while lighter stars pick up speed and head for the outer edges. The more often collisions happen the more dramatic the results – pushing the smaller stars ever faster towards the periphery and creating exotic objects. What no earthly photo can ever show is that 47 Tucanae contains at least twenty millisecond pulsars – better known as neutron stars. Can you imagine a sun that rotates on its axis a few hundreds to one thousand times a second? Just imagine the power. According to scientists, such peculiar objects are generally thought to have a companion from which they receive matter. Close interacting binaries and bright cataclysmic binaries… dwarf novae and nova-like variable candidates…. They all make their home here closer to the heart.

Now, keep binoculars and telescopes handy we’re off to the next globular cluster – NGC 362 (RA 1 : 03.2 Dec -70 : 51). At near magnitude 7 and 12 arc minutes in size, this much smaller globular was discovered by James Dunlop on August 1, 1826. You’ll find it compact and very pretty in a smaller scope and well-resolved in large aperture. In 1980 this particular star cluster was compared to a similar one, only to find it was about 3 billion years younger!

Ready for that great big galaxy you can see without any optical aid? Then say hello to the Small Magellanic Cloud. This dwarf galaxy is part of our own local galaxy group which includes the Milky Way, Large Magellanic Cloud, the Andromeda Galaxy and more. It is believed the SMC was once a barred spiral galaxy that was disrupted by the Milky Way – and now an irregular galaxy which still contains a central bar structure. Located about about 200,000 light-years away, you’ll find a host of other great NGC objects inside as well, such as NGC 265, NGC 290, NGC 346, NGC 347and NGC 602. Enjoy!

Sources:
Chandra Observatory
SEDS
Wikipedia
Chart courtesy of Your Sky.

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The small southern constellation of Triangulum Australe was first introduced in 1589 by Petrus Plancius on a celestial globe which was later added to Johann Bayer’s atlas – Uranometria – in 1603. The constellation, then named “Triangul Australe” was later adopted by the IAU as a member of the 88 modern constellations. It spans 110 square degrees of sky, ranking 83rd in size. Triangulum Australe has 3 main stars in its asterism and 10 Bayer Flamsteed designated stars within its confines. It is bordered by the constellations of Norma, Ara, Circinus and Apus. Triangulum Australe is visible to all observers located at latitudes between +25° and ?90° and is best seen at culmination during the month of July.

Since Triangulum Australe is considered a “new” constellation, there is no mythology associated with it – only how its name came to be. During the late 1600s Dutch navigators Pieter Dirkszoon Keyser and Frederick de Houtman were exploring the southern hemisphere and part of their work dealt with charting the southern stars as well. Petrus Plancius, a celestial cartographer, had depicted a “triangle” of stars on his globe which appeared south of Argo Navis and with the Southern Cross. Their job was to confirm it! Later, Abbe Nicolas Louis de Lacaille would also journey to the southern hemisphere to chart the heavens as well, and on his maps he named this distinctive configuration “Triangle Austral ou le Niveau”. Because so many differing names and designations led to confusion, the International Astronomical Union eventually set the borders – and the name – at Triangulum Australe, the “Southern Triangle”.

Let’s begin our binocular tour with the brightest star – Alpha Trianguli Australis – the “a” symbol on our chart. Located approximately 415 light years from Earth and properly named Atria, here we have an orange K-type bright giant star which may harbor a spectroscopic companion. While it quietly fuses helium into carbon and oxygen in its deep core, Atria shines over 4900 times brighter than our own Sun! Classed as a barium star, this hybrid giant blows cool stellar winds hot surrounding magnetic corona. What makes Atria so curious is an abundance of x-ray emissions, which suggests the presence of a nearby white dwarf star!

Now, get out the big telescope for Beta – the “B” symbol on our chart. Alpha Trianguli Australis is located about 40 light years from our solar system and it is a true binary star. The primary component, Beta Trianguli Australis A, is a yellow-white F-type giant star, but you’ll need some aperture to see the 14th magnitude disparate companion separated from the primary by 155 arcseconds!

Ready for a change? Then let’s take a look with binoculars at X Trianguli Australis, a very fun variable star! Almost any optical aid will help you spot this clever little red carbon variable. It’s around 1500 light years away and at the dimmest it will appear to be about stellar magnitude 7. Keep an eye on it, though… Because it will brighten to magnitude 6!

For either binoculars or telescopes, let’s have a look at splendid open cluster, NGC 6025 (RA 16 : 03.7 Dec -60 : 30). On the edge of being detectable to the unaided eye, apparent magnitude 5, NGC 6025 spans about 12 arc minutes in size and was discovered by Nicolas Louis de Lacaille. For deep sky fans and those working on challenge objects, you’ll find it is included in Sir Patrick Moore’s Caldwell Catalogue as Caldwell 95 and on the Astronomical League’s Southern Sky Binocular List. Even small optics can easily resolve out about 30 or so stars from this rich galactic cluster! NGC 6025 has been highly studied to see if it contains binary stars, or rapidly rotating stars with spots that might pose as unseen companions.

Don’t forget the big scope for other challenge objects like planetary nebula NGC 5979 (RA 15 : 47.7 Dec -61 : 13). Nearly stellar in size, this small planetary will require the aid of a nebula filter to pick its small disc out from the surrounding field. There are also two very faint galaxies, NGC 6156 (RA 16 : 34.8 Dec -60 : 36) and NGC 5938 (RA 15 : 36.4 Dec -66 : 52), but both their size and magnitude will make them nearly impossible for all but the largest of telescopes.

Sources:
Wikipedia
University of Wisconsin
University of Illinois
Chart Courtesy of Your Sky.

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Triangulum, located just north of the ecliptic plane, was one of the 48 original constellations listed by Ptolemy, and remains one of the 88 modern constellations. It spans 132 square degrees of sky and ranks 78th in size. Triangulum has 3 mains stars in its asterism and 15 Bayer Flamsteed designated stars within its confines. It is bordered by the constellations of Andromeda, Pisces, Aries and Perseus. Triangulum can be seen by all observers located at latitudes between +90° and ?60° and is best seen at culmination during the month of December.

As one of the very few constellations to be named after an object instead of a mythical figure or animal, one of the first names of this constellation was Sicilia – which represented the island of Sicily. This tale came about because it was believed that Ceres, the patron goddess, had begged Jupiter to immortalize her home in the stars. For a time, this region of sky was also known as Triangulum Minus, as recorded by Johannes Hevelius. It was formed from the southern parts of his Triangula, and the name quickly fell into disuse. It eventually simply took on the Latin term for its three primary stars the “triangle” and has been referred to as Triangulum ever since.

Let’s begin our binocular tour of Triangulum with its brightest star – Beta – the “B” symbol on our chart. Beta often goes by the name Deltotum, which is a Greek letter – Delta – which also resembles a triangle. Beta is a white A-type giant star located about 124 light years from Earth. Now switch off to the second brightest star – Alpha – the “a”. Its name is Mothallah – the head of the triangle. Guess what? It’s a binary star! While you won’t be splitting this spectroscopic yellow-white F-type subgiant binary star with any optics, it’s still fun to know that its diameter is about 3 times as large as the Sun and that its companion orbits it in less than 2 days from a distance of under 4 million miles. That’s almost touching in astronomical terms! By the way… They’re both about 65 light years away from our solar system. For a binary star you can separate in a telescope, have a look at 6 Trianguli. Its 5.3 and 6.9 components are easy to pick apart even with a small telescope because they are separated by almost 40 arc seconds.

Now, you might need to get out your telescope for the next object… A long term variable star named R Trianguli (RA 02: 34 DEC +34: 03). Depending on when you start, you may have a long time to wait to see changes, because R takes 266 days to go from stellar magnitude 5.7 to an almost invisible 12.4! R Trianguli is an “M-class” Red giant star who owes its changes to pulsations. As it expands, it becomes brighter… As it contracts, it becomes faint. What an incredible star to watch!

For binoculars and rich field telescopes, it’s time to head towards the ghostly galaxy, Messier 33 (RA 1 : 33.9 Dec +30 : 39). While this incredible spiral galaxy has an apparent magnitude of 5.7, you’re not going to find it quite as easy to find as you might think. Why? Because a lot of times you’re going to be missing the forest because you’re looking at the trees. M33 is huge! Located some approximately 3 million light-years away, the “Pinwheel Galaxy” contains a host of its own NGC objects and can often be spotted without optical aid from a dark sky location. One of the most positive ways to locate it is to use the very lowest magnification eyepiece you have available and work your way up to study each portion. It is the third largest galaxy in the Local Group, a group of galaxies that also contains the Milky Way Galaxy and the Andromeda Galaxy, and it may be a gravitationally bound companion of the Andromeda Galaxy.

The Triangulum Galaxy was probably discovered by Giovanni Batista Hodierna before 1654, who may have grouped it together with open cluster NGC 752. It was independently discovered by Charles Messier in 1764, who catalogued it as M33 on August 25. M33 was also catalogued independently by William Herschel on September 11, 1784 number H V.17. It was among the first “spiral nebulae” identified as such by Lord Rosse. Herschel also cataloged The Triangulum Galaxy’s brightest and largest H II region (diffuse emission nebula containing ionized hydrogen) as H III.150 separately from the galaxy itself, which eventually obtained NGC number 604. As seen from Earth NGC 604 is located northeast of the galaxy’s central core, and is one of the largest H II regions known with a diameter of nearly 1500 light-years and a spectrum similar to the Orion Nebula. Herschel also noted 3 other smaller H II regions (NGC 588, 592 and 595).

In 2005, using observations of two water masers on opposite sides of Triangulum via the VLBA, researchers were, for the first time, able to estimate the angular rotation and proper motion of Triangulum. A velocity of 190 to 60 km/s relative to the Milky Way is computed which means Triangulum is moving towards Andromeda. In 2007, a black hole about 15.7 times the mass of the Sun was detected in the galaxy using data from the Chandra X-ray Observatory. The black hole, named M33 X-7, orbits a companion star which it eclipses every 3.5 days. Although we can never see it, we can certainly enjoy this faint galaxy for all the mysteries it holds!

Keep your telescope handy as you head off for our next galactic designation, NGC 925 (RA 2 : 27.3 Dec +33 : 35). At magnitude 10 and nearly 10 arc minutes in size, it is also fairly easy for a small telescope and large binoculars. This face-on presentation spiral galaxy is also part of the Hubble Space Telescope project for extra-galactic distances which use Cepheid variable stars to help judge that vast expanse of space between us. Look for a bright core region with elongated wispy spiral galaxy structure!

Now try your hand, and your telescope, and NGC 672 (RA 1 : 47.9 Dec +27 : 26). At close to magnitude 11 and 7 arc minutes in size, it is a bit more of a challenge, but large telescopes will find it and interacting galaxy IC 1727 in the same field of view. The pair is believed to be separated by about 88,000 light years – or about their own diameters. While you won’t catch an outstanding amount of detail in either one, you may begin to resolve out some lumpy areas of star birth!

Last, but not least, is NGC 784 (RA 2 : 01.3 Dec +28 : 50). At magnitude 12 and about 6 arc minutes in size, it is the smallest and faintest challenge yet. It is a barred-spiral galaxy presented nearly edge-on, and it is very diffuse. In spite of its expected small distance, NGC 784 has not yet been resolved into stars and is still being studied for velocity and kinematics. Good luck!

Sources:
SEDS
Wikipedia
Chart courtesy of Your Sky.