Category: Astronomy

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.

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The small constellation of Telescopium is located just south of the ecliptic plane and was originally charted by Abbe Nicolas Louis de Lacaille who named it. It was later adopted by the IAU as one of the modern 88 constellations. Telescopium spans 252 square degrees of sky – ranking 57th in size. It has 2 primary stars in its asterism and 13 Bayer Flamsteed designated stars within its confines. Telescopium is bordered by the constellations of Ara, Corona Australis, Indus, Microscopium, Pavo and Sagittarius. It is visible to observers located at latitudes between +40° and -90° and its primary stars are best seen at culmination during the month of August.

Since Telescopium is considered a “new” constellation, there is no mythology associated with it – only Abbe Nicolas Louis de Lacaille’s love of all things science and what Telescopium is meant to represent – the telescope of Sir William Herschel. In Lacaille’s time, it was called “Beta Telescopii” and when represented on Johann Bode’s charts, it pointed northwards, towards Sagittarius and Corona Australis. Since Bode actually depicted it clear up into Ophichus, he also changed the name to “Tubus Astronomicus” as well. Later, both the name – and the constellation – became more abbreviated as it was adopted by the International Astronomical Union.

Let’s begin our binocular tour of Telescopium with its brightest star – Alpha – the “a” symbol on our chart. While Alpha is far from bright to our vision, this class B (B3) blue subgiant star shines more than 900 times brighter than our own Sun from a distance of 250 light years away. It is a young star, just beginning to evolve away from a core-hydrogen-fusing dwarf. While it is rotating very slowing, Alpha is also chemically peculiar, because it is a helium rich star with very strong stellar magnetic fields. It is believed that it may someday evolve into a massive white dwarf like Sirius-B.

Now aim your binoculars towards Delta – the “8” symbol. It won’t take long to discover this designation is shared by two stars! That’s right, we’re looking at an optical double star. Delta 1 and Delta 2 are both blue-white B-type subgiant stars, but Delta 1 (slightly brighter) is approximately 800 light years from Earth, while Delta 2 is closer to 1,100 light years distant!

Are you ready for Kappa? That’s the “k” symbol on our chart. Kappa Telescopii is also a visual double star. It is a yellow G-type giant star located 293 light years from our solar system.

Get out large binoculars or a small telescope for a look at a very rare type of variable star – RR Telescopii (RA 20 04 18.54 Dec -55 43 33.2). Here we have an example of what is called a Symbiotic Nova. According to the work of F.L. Crawford: “The optical spectrum of RR Tel is very rich in emission. By comparing the results of this study with previous publications on the subject, it is found that the RR Tel system is advancing towards higher degrees of excitation. It is also shown that several nebular lines (for example, [OIII] 4363 Angstroms and NeIV 4714 Angstroms) demonstrate component structure, perhaps caused by the different densities of the emitting plasmas.” Also, infrared and optical photometric and spectroscopic observations of the symbiotic nova RR Telecopii are used to study the effects and properties of dust in symbiotic binaries containing a cool Mira component, as well as showing “obscuration events” of increased absorption, which are typical for such Mira-type variable stars. RR Telescopii erupted in 1944 and took nearly 1600 days to reach maximum. At its lowest, RR can be as dim as magnitude 11 – or as bright as magnitude 7!

Keep a telescope handy to have a look at globular cluster NGC 6584 (RA 18 : 18.6 Dec -52 : 13). At around magnitude 9, this 8 arc minute sized globular will delight you. Discovered by James Dunlop on June 5, 1826 and cataloged originally as Dunlop 376, you will pull a lot of nice resolution out of the core region with larger aperture. A lot of photometry work has been done on this particular star cluster – looking for calcium abundances, blue straggler stars and hot stars located in the galactic halo region.

Now aim your large telescope towards challenging planetary nebula IC 4699 (RA 18 : 18.5 Dec -45 : 59) At magnitude 12 and nearly stellar in size, this particular planetary nebula will be difficult to distinguish from the field without the aid of a nebula filter which will aid in revealing the small disc.

Sources:
SEDS
Wikipedia
Chart Courtesy of Your Sky.