Category: Guide to Space

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The southern circumpolar constellation of Mensa was created by Nicolas Louis de Lacaille and was originally named Mons Mensae. It was later changed and adopted by the International Astronomical Union and accepted as one of the permanent 88 modern constellations. Mensa encompasses only 153 square degrees of sky – ranking 75th in size. It possesses no bright stars and only 4 stars form its cup-shaped asterism. There are, however, 16 Bayer/Flamsteed designated stars within its confines. Mensa is bordered by the constellations of Chamaeleon, Dorado, Hydrus, Octans and Volans. It is visible to observers positioned at latitudes between +18° and ?90° and is best seen at culmination during the month of January.

There is an annual meteor shower connected with this constellation is called the Delta Mensids – so named because the meteors appear to radiate from a point in the sky close to the star Delta Mensae. The meteor shower begins on or about March 14 and lasts until about March 21. Studies have shown there may be two seperate meteoriod streams responsible for this shower – one which causes a maximum on or about March 18 and another on or about March 19 with the debris suspected to have originated from Comet Pons, which was visible in 1804. Just as Mensa isn’t much of a constellation, the Delta Mensids aren’t much a meteor shower, either… The maximum fall rate only averages about 1 to 2 per hour at most.

Since Mensa is considered a relatively “new” constellation, there is no mythology associated with it, but there are several legends about how it came to be so named. It is believed that Nicolas Louis de Lacaille called in “Mons Mensae” in honor of Table Mountain, which overlooked his home observatory in Cape Town, South Africa. Since the top of the flat mountain was often covered by clouds, and the stellar formation is topped by the Large Magellanic Cloud, the name seems to fit perfectly! There is also a tall tale of a man who loved to smoke his pipe – but his wife forbid him to in the house. As a result, he would climb to the table mountain to enjoy the view while he smoked and one fine day he met the devil. Of course, he bragged how much he could smoke, so they engaged in a contest. The result left the mountain in a fog and the Magellanic Cloud in the stars! Other legendary tales suggest that our neighboring galaxy is either a god or a monster left on the high hill to guard the cape from unwary travelers… But no matter how Mensa came about its name, it is still a very faint constellation and will require patience and practice to see.

When you are ready, let’s start with a binocular tour of Mensa and its brightest star, Alpha – the “a” symbol on our map. Just barely visible to the unaided eye at magnitude 5.09 Alpha Mensae is a main sequence dwarf star located about 33 light years away from Earth. Shining away at about 80% the luminosity of our own Sun, Alpha is very similar. It is also a slow stellar rotator, taking about 32 days to complete a full rotation on its axis. At around 10 million years old, it comes within 7% of being about the same size as Sol, too… But we better enjoy it while we can. Even as we speak, Alpha Mensae is heading away from us at a speed of 35 kilometers per second!

Now aim your binoculars towards Beta Mensae – the “B” symbol on our map. Beta has the distinction of being a foreground star on the southern edge of the Large Magellanic Cloud! It’s a G-type giant star – again similar to our own Sun. What’s that? Try a main sequence star that’s happy in the “Yellow Evolutionary Void”. Unlike Alpha, it’s a lot further away… About 640 light years from our solar system.

Next stop? Pi Mensae – the “TT” symbol on our map. Pi is a yellow subgiant star with a high proper motion. Located approximately 60 light years away, Pi simply dwarfs our Sun in terms of mass, size, luminosity, temperature, and metallicity, yet it’s 730 million years younger! What makes it special? Pi ranks 100th on the list of top 100 target stars for the planned Terrestrial Planet Finder mission. On October 15, 2001, that search became successful when one of the most massive superjovian planets (HD 39091 b) ever found was discovered orbiting Pi Mensae. While it currently has a very eccentric orbit and takes approximately 2064 days (5.65 years) to revolve around its parent star, it does pass through a habitable zone – which means it probably would have disrupted the orbits of Earth-like planets long ago, either sending them into the parent star, or off into interstellar space.

While touring Mensa in binoculars, be sure to take in the full depth and breadth of the Large Magellanic Cloud which also crosses into Dorado. For a telescope challenge, try locating an open cluster in another galaxy! NGC 1711 (RA 04:50:36.0 Dec -69:59:06.0) is a very rich, 10th magnitude galactic star cluster which borders on the edge of being globular. It is actually a very young object whose data serves as a base for the study of mass functions and for the comparison with theoretical cosmological models.

For even more telescope challenges, try globular cluster NGC 2019 (RA 05:31:56:0). Also at home in the LMG, this small, bright-cored globular is a worthy target for mid-sized telescopes. Other globular clusters include NGC 2134, NGC 2065, NGC 2107, NGC 2058, NGC 1943, NGC 1987 and NGC 2121 in descending order of magnitude. These were all discovered by Sir William Herschel and are all located in the Mensa portion of the LMG.

Mensa is also home to quasar PKS 0637-752 (RA 06:35:46 Dec -75:16:12) – the first study of the Chandra X-Ray Observatory. When gathering first light on August 15, 1999, Chandra presented the world with a pair of images which revealed the quasar PKS0637-752 – a bright distant galaxy. Quasars like this are fairly “normal” galaxies which contain an active and massive black hole at its center. The brightness of the quasar is a result of material falling into the black hole. As well as the bright core of emission around the black hole, these images revealed a jet of material ejected from the black hole undergoing a remarkably sharp turn. With overlaying radio contours and optical images provided by Chandra, the newly revealed x-ray jet displayed the power far great than any radio jet ever recorded. It produces as much energy as 10 trillion Suns, all from a volume smaller than our own solar system!

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

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Located north of the ecliptic plane, the constellation of Lyra is one of the original 48 constellations listed by Ptolemy, and remained as part of the 88 modern constellations recognized by the International Astronomical Union. Spanning only 286 square degrees of sky, Lyra ranks 52nd in size amongst the others, but contains the second brightest star in the northern hemisphere. Five main stars comprise its asterism and 25 Bayer Flamsteed designated stars are confined within its realm. Lyra is bordered by the constellations of Draco, Hercules, Vulpecula and Cygnus. It is visible to all viewers located at latitudes between +90° and ?40° and is best seen at culmination during the month of August.

There are two meteor showers associated with the constellation of Lyra. On or about April 22 of each year is the peak date of the annual Lyrid Meteor Shower. Its radiant – or where the meteors seem to originate – is around the bright star Vega. You can expect to see about 15 meteors per hour on the average when the constellation is at its highest on a dark night. They are bright, long-lasting meteors which leave long trails… the offspring of Comet Thatcher! The stream itself generally lasts through the beginning of May. By June 16, we return once again to hit another portion of the same stream, but with less force. The gravity of Jupiter and time has robbed this particular branch of the larger particles, so these meteors are much fainter. The fall rate also averages about 15 per hour maximum on a dark night – but the meteors are far fainter and tend to be more blue in color.

In mythology, Lyra is the “lyre”… a sort of hand-held harp. According to ancient Greeks, the messenger god Hermes created the lyre from the washed up body of a large tortoise shell which he covered with animal hide and antelope horns. He later gave it to Apollo as a present – who then presented it to his son Orpheus. There’s a wonderful quote by poet J.R. Lowell: “So there it lay, through wet and dry… As empty as the last new sonnet, Till by and by came Mercury, And, having mused upon it, ‘Why, here,’ cried he, ‘the thing of things In shape, material, and dimension! Give it but strings, and, lo, it sings, A wonderful invention!’ When Orpheus’ wife died, he was so grief stricken, he threw his harp into the Milky Way, wishing never to see it again. As legend has it, Apollo sent an eagle to retrieve it and set it among the stars. That is why you will also see it often depicted with wings as well. And so, the Lyre became part of the sky and it doesn’t take a whole lot of imagination to see its shape in the stars!

Now, let’s start our binocular tour of Lyra with its brightest star – Alpha – the “a” symbol on our map. Best known as Vega, it measures up as the second brightest star in the northern celestial hemisphere and the fifth brightest star in the night sky. Located 25.3 light years from Earth, this massively luminous A-type star is a suspected Delta-Scuti type variable star and its the first to have its spectrum photographed. Historically, Vega served as the northern pole star at about 12,000 BCE and will do so again at around 14,000 CE. Compared to our Sun, Vega is a youngster – with an unusually low abundance of the elements with a higher atomic number than that of helium. It’s also a rapid rotator – spinning completely on its axis in about 12 hours. So fast that the radius of the equator is 23% larger than the polar radius! Another thing Vega does have is an excess of infra-red radiation. What’s the cause? Possibly a circumstellar disc. Detections of irregularities in the disc means there’s a distinct chance of a planet the size of Jupiter orbiting there! I wonder how fast it orbits?

Keep your binoculars in hand and take a look at Beta Lyrae – the “B” symbol on our map. Now here’s a trick star system if there ever was one! Located 882 light-years from our solar system and named Sheliak, the “Tortoise” is very definitely a binary star – but not just any binary star. Sheliak is an eclipsing binary star. And not just any eclipsing binary star, but an eclipsing contact binary star system made up of a blue-white dwarf (B7V) star and a white main sequence (A8V) star. The two stars are close enough that material from the photosphere of each is pulled towards the other, drawing the stars into an ellipsoid shape. Beta Lyrae is the prototype for this class of eclipsing binaries, whose components are so close together that they deform by their mutual gravitation! In a period of period of 12.9075 days you’ll see this star swing drop from magnitude 3.4 to magnitude 4.6 – and it’s very noticeable. While you’ll never split the AB pair, you can very easily pick out the 7th magnitude C component with just your binoculars!

Don’t loose the binoculars yet. Head up to Delta 1 and Delta 2 – the figure “82” on our map. While the Delta pair is strictly an optical double star – this blue white and red pair of giant stars is very pleasing in binoculars. Slightly brighter, blue/white Delta 1 is located about 900 light years away and reddish Delta 2 is only about 720. Most of the time they are only separated by just a few tenths of a magnitude in brightness – but watch Delta 2 – because it is also a variable star and can become twice as dim! Did you happen to notice the pair is in a very stellar field? Good reason. Delta 1 and 2 are part of an open star cluster known as Stephenson 1.

Ready to have a look at Epsilon 2, the backwards “3” on our map? This is the famous “Double Double”. In binoculars you will see what appears to be a nice, white double star – but put a telescope at high magnification on it and watch what happens. Both stars will resolve into binary stars! The Epsilon Lyrae pair is one of the most observed multiple star systems in the heavens and the 162 light year distant mates make for a great time in just about any telescope – even in the most light polluted skies. Not only is each pair of stars physically connected to each other – but both pairs of stars are gravitationally bound – requiring over 12 centuries to complete their orbits. Are they close? You bet. If you have to wait for a moment of stability for them to cut themselves apart, then consider they’re only separated by about 0.16 of a light year!

And now for “Lucky 13″…

You can use binoculars, because star 13 is the infamous R Lyra – a proto-type variable star. Even though R is 350 light years away, its the brightest true (intrinsic) variable in the entire constellation. Sure, Beta looks brighter – but its changes come about because of eclipses – not because of internal processes. Inside of star 13 some mighty big changes are happening. Having progressed in its stellar evolution, this class M5 red giant star is also a semi-regular variable known as an SRb star – or a low-level, long period pulsating variable like Mira. Its changes are very noticeable, too… flipping between magnitude 3.9 and 5.0 over a 46 day period. Yes, it’s dying. And not a pretty death, either. Its mass is uncertain… It expands and contracts… its stellar temperature ranges from 3175 Kelvin to 3750 Kelvin… it has a dead carbon-oxygen core surrounded by fusing shells of helium… Apparently being star 13 isn’t so lucky!

Ready to get Messier? The go directly between Gamma and Beta Lyrae to grab the “Ring”… The only and only planetary nebula – M57. Discovered by French astronomer Antoine Darquier in 1779, the Ring Nebula was cataloged later that year by Charles Messier as M57 (RA 18 53 35 Dec +33 01 45). In binoculars the Ring will appear as slightly larger than a star, yet it cannot be focused to a sharp point. To a modest telescope at even low power, Messier 57 turns into a glowing donut against a wonderful stellar backdrop. The accepted distance to this unusual structure is about 1,400 light-years, and how you see the Ring on any given night is highly dependent on conditions. As aperture and power increase, so do details, and it is not impossible to see braiding in the nebula’s structure with scopes as small as 8″ on a fine night, or to pick up the star caught on the edge in even smaller apertures. Like all planetary nebulae, seeing the central star is considered the ultimate achievement in viewing. The central itself is a peculiar bluish dwarf which gives off a continuous spectrum, and might very well be a variable. At times, this shy, near 15th magnitude star can be seen with ease with a 12.5″ telescope, yet be elusive to even 31” in aperture weeks later. No matter what details you may see, reach for the “Ring” tonight. You’ll be glad you did.

More? Then hang on and let’s go globular cluster hunting as we capture Messier 56! Located roughly midway between Beta Cygni and Gamma Lyrae (RA 19 15 35.50 Dec +30 11 04.2), this class X globular was discovered by Charles Messier in 1779 on the same night he discovered a comet, and was later resolved by Herschel. At magnitude 8 and small in size, it’s a tough call for a beginner with binoculars, but is a very fine telescopic object. With a general distance of 33,000 light-years, this globular resolves well with larger scopes, but doesn’t show as much more than a faint, round area with small aperture. However, the beauty of the chains of stars in the field makes it quite worth the visit!

While you’re there, look carefully: M56 is one of the very few objects for which the photometry of its variable stars was studied strictly with amateur telescopes. While one bright variable had been known previously, up to a dozen more have recently been discovered. Of those, six had their variability periods determined using CCD photography and telescopes just like yours!

For a big telescope challenge, try your luck with NGC 6702 (RA 18:47.0 Dec +45:42). This magnitude 12, this small, faint elliptical galaxy was home to a supernovae event in 2002 and has a high evolved and highly studied globular cluster system. For a slightly brighter galaxy, look up very nearby NGC 6703 (RA 18:47.3 Dec +45:33) to the southeast. Also an elliptical galaxy, but a full magnitude brighter and slightly larger, you’ll pick out a more round signature in this one. Studies have found a dust lane in the center of NGC 6702 indicating a recent gaseous galaxy merger event meaning this pair are truly and interacting set.

Sources: SEDS, Wikipedia
Chart courtesy of Your Sky.

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Located north of the ecliptic plane, the dim constellation of Lynx was first introduced in the 17th century by Johannes Hevelius in 1687 and later recognized as one of the 88 modern constellations by the International Astronomical Union. According to legend, Lynx is so named because it is a relatively faint constellation, and one would supposedly need the eyes of a lynx to see it. Covering 545 square degrees of sky, it ranks as the 28th largest constellation. Although only 4 main stars form its asterism, Lynx contains 42 stars with Bayer Flamsteed designations. It is bordered by the constellations of Ursa Major, Camelopardalis, Auriga, Gemini, Cancer, Leo and Leo Minor. Lynx is visible to all observers located at latitudes between +90° and ?55° and is best seen at culmination during the month of March.

Since Lynx wasn’t recognized as a constellation until the 17th century, it has no mythology associated with it and it would seem that Hevelius was merely trying to fill in the spaces between the constellations by making up a mythical figure – or was he? Actually, by doing a little research into the life and times of Johannes Hevelius, you might find that he was a very interesting figure and very devoted to nature studies – in particular North America. At the time the lynx was a native of Europe, but hunted almost to the point of extinction. Not so in a new land. To Native Americans, the lynx was legendary – an elusive, ghost-like animal that sees without being seen. It was known as “the keeper of secrets of the forest” and to see it was quite magical – knowing that its secrecy was its strength. Oddly enough, the lynx was chosen as the emblem of the Accademia dei Lincei (“Academy of the Lynxes”), one of the world’s oldest scientific societies. Its piercing vision was invoked symbolically as characteristic of those dedicated to science. So perhaps good old Hevelius wasn’t quite as prone to “filling in the blanks” as we thought, eh?

Now, grab your binoculars and let’s take a look at the only star that Bayer (shame on him) got around to giving a Greek letter to – Alpha Lyncis – the “a” symbol on our map. At 220 light years from Earth, class K (K7) giant star Alpha has no proper name, yet it still burns merrily away at a rough stellar temperature of 3860 degrees Kelvin. It is about a billion and a half years old and perhaps not very special except for it is about 700 times brighter than our own Sun. However, take a look at its twin, star 31. Now, this one did get a name – Alsciaukat – the “Thorn”. It is almost identical to Alpha in every respect, only slightly further away at 390 light years. Their luminousities, their temperatures, their sizes, their ages… Almost twins! Only this time Alsciaukat is also a slight variable star, changing by about .05 magnitude. Why is it a bit different? Chances are it is brightening for the second time – gearing up to become a long term variable like Mira.

For the telescope, have a look at 38 Lyncis. Hevelius wasn’t without a sense of humor, because he named this one Maculosa and Maculata, which synonymously mean “The Spotted One”. Can you guess why? That’s right. It’s because 38 Lyncis is a binary star. Located about 120 light years from our solar system, this star has several components. The 3.9 primary star is also a spectroscopic binary, but look for the near 7th magnitude C star to split easily away and a very widely spaced 11th magnitude D companion, too. While the primary star usually appears to be white in color, look for a slight green tinge, as well as some blue coloration to the C star, too. The double star is on many observing lists!

Now, check out wide visual triple star, 12 Lyncis. Also on a host of observing lists, this one is very easy and very rewarding to small telescopes. Look for a 5.4 primary star accompanied by the 6.0 B star and the further spaced 7.3 magnitude C star. Located about 230 light years away, you can thank Otto Struve for discovering this one in 1828!

For variable star fans, be sure to keep an eye on R Lyncis (RA 07:01:18 Dec +55:19:50). It’s a great Mira-type variable that also does a disappearing act! For a long period of time, R appears as a rather ordinary red 7th magnitude star…. then it drops off the map when it falls down to magnitude 14.3. Weird? Darn right. R Lyncis belongs to a small group of long-period variables with a “S” spectrum – a ‘cool red giant’ that shows the presence of zirconium oxide.

Now we’ll put our “cat’s eyes”, grab our telescopes and go in search of one of the most distant objects in our Galaxy – NGC 2419 (RA 07:38:08.51 Dec +38:52:54). As a telescopic object only, this magnitude 11.5 study requires clear dark skies and at least 150mm of aperture. Since Lynx is a difficult constellation, you will find this easier by going 7 degrees north of Castor. You will know if you have the correct field if two stars appear to the western edge of a hazy patch. There is a very good reason “why” this elusive globular cluster is so special! Most commonly known as “the Intergalactic Wanderer”, the NGC 2419 is so distant that it was at one time believed to actually be outside our own galaxy. Almost all globular clusters are found within our galactic “halo” – a region which exists about 65,000 light years around the galactic center. Our faint friend here is at least 210,000 light years from where it should be! When I tell you it’s out there… I’m not kidding. The NGC 2419 is as distant as our galactic “neighbors”, the Magellanic Clouds! But don’t worry, our Galaxy has sufficient gravitation to keep “the Intergalactic Wanderer” around long enough for you to capture it for yourself!

Ready for more? Then keep the telescope out as we journey towards spiral galaxy NGC 2683 (RA 08:52.7 Dec +33:25). Located 16000 light years away from our own Milky Way Galaxy, this superb edge-on was discovered by William Herschel on February 5, 1788. Holding a bright and respectable magnitude 10 puts it well within realm of smaller telescopes and larger ones will be able to pick out varying degrees of spiral galaxy structure, including hints of a dark dust lane and a bright, bulging nucleus. It’s a Herschel 400 object, so be sure to mark your notes!

Need a challenge? Then try your luck with NGC 2776 (RA 9:12.2 Dec +44:57). At near 12th magnitude, this small spiral galaxy isn’t going to be easy, but a large telescope can handle it. Viewed perfectly face-on, look for the signature round structure with a bright core region and some resolution of arms during good seeing conditions. More? How about 13th magnitude barred spiral galaxy IC 2233 (RA 08:13:58 Dec +45 44:32). Sometimes known as the “Needle” because of its edge-on presentation!

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

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Located south of the ecliptic plane, the constellation of Lupus was once associated with Centaurus, but was listed as a separate constellation in Ptolemy’s Almagest. It survived to become one of the 88 modern constellations recognized by the International Astronomical Union. Lupus covers around 334 square degrees of sky and contains 9 stars in its asterism with 41 Bayer Flamsteed designated stars confined within its area. It is bordered by the constellations of Norma. Scorpius, Circinus, Centaurus, Libra and Hydra. Lupus can be seen by all observers located at latitudes between +35° and ?90° and is best seen at culmination during the month of June.

In mythology, Lupus represents the Wolf and was once thought to represent the wild African dog associated with the mythical first king of Arcadia. The stars were only a representation of some type of creature – a beast – caught by the Centaur and about to be slain. Actually, no animal even entered the picture until Ptolemy called it Lupus and the Latin translation transformed it from the “beast” into a wolf!

Let’s start our binocular tour of Lupus with Alpha Lupi – the “a” symbol on our map. Known as Men, the “Star of Fortune” is a Beta Cephii variable star located about 550 light years from Earth. Its magnitude changes happen every 6 hours and 14 minutes – just like clockwork – but they aren’t very radical. Even a sharp-eyed observer isn’t likely to notice a .03 stellar magnitude drop in this blue giant star! But pay a little closer attention. Do you see a companion there? Even though it’s only an optical double star, it helps to make Men just a little bit more interesting!

Now turn your binoculars towards Beta Lupi – the “B” symbol on our map. Kekouan is also a blue giant star and is similarly distant at about 525 light years from our solar system. It’s another one of those hot class B stars that shine in that wonderful blue/white light and part of the expanding “Upper Centaurus Lupus” (UCL) OB association. What would it be like if it were closer? Try 13,600 brighter than our Sun. It’s a subgiant right near the end of its life and very near to becoming a red supergiant star…. and one day… a supernova!

Travel on in binoculars to the next star in the Association – Gamma Lupi – the “Y” symbol on our map. Gamma’s proper name is Thusia, meaning “The Sacrifice”, but the only thing you’ll have to sacrifice is a moment of your time to take a look through the telescope, because Thusia is a binary star. Located 567 light years from Earth, the blue/white primary is a giant star in its own right, accompanied by a very close companion whose orbit takes it nearly edge on from our perspective with a maximum separation of about .68″. Also try your luck with Epsilon Lupi, the “E” symbol. It, too, is a close binary star with about the same separation and 3.5 and 5.5 magnitude components.

Keep the telescope handy to look up NGC 5824 (RA 15:03:58.5 Dec -33:04:04). Located about 105 light years from where you’re reading, this globular cluster was first discovered by James Dunlop and recovered independently by E.E. Barnard. At around magnitude 9 and a little on the small side, you’ll find it relatively bright with a slightly off-centered, concentrated core region and a bit of resolvability around the edges for larger aperture.

Try your hand at planetary nebula IC 4406 (RA 14:22:26 Dec -44:09:04) too. This bi-polar nebula often goes by the popular name “The Retina Nebula” and will appear almost square because of the angle on which we see it. Chances are, it’s a hollow cylinder, just like all torus shaped planetaries – we just happen to be catching it from the side. At magnitude 10, it’s not going to wow you like the Hubble images will, but it is still a very worthy target for a larger telescope that will show a little detail.

Small, rich field telescopes and larger binoculars will be happy to take a look at NGC 5822 (RA 15:05.2 Dec -54:21). Spanning 40 arc minutes and shining away at magnitude 7, this well populated open cluster is so huge it will appear like a star cloud. Don’t be fooled into thinking your resolving it when you’re picking out foreground stars! NGC 5822’s population runs into the hundreds and its members average around stellar magnitude 13 and fainter. It will be hard to pick out from the rich Milky Way Galaxy star fields!

Don’t leave the telescope until you’ve tried galactic cluster NGC 5749 (RA 14 48.9 Dec -54 31). In a low power eyepiece, this star cluster will look like a just a loose group of stars which almost blend with the background star field. Containing around 35 members with the brightest about magnitude 10, keep to lower magnification to keep the target in site!

Cutting through our Milky Way galaxy at a rough angle of about 18 degrees is a disc-shaped zone called Gould’s Belt. Lupus is part of this area whose perimeter contains star forming regions which came to life about 30 million years ago when a huge molecular cloud of dust and gas was compressed – much like in the Orion area. In Lupus we find Gould’s Belt extending above the plane of the Milky Way!

Locate Theta Lupi and head around five degrees west for NGC 5986 (RA 15 46 03 Dec 37 47 10), a 7th magnitude globular cluster which can be spotted with binoculars with good conditions. While this Class VII cluster is not particularly dense, many of its individual stars can be resolved in a small telescope. Now sweep the area north of NGC 5986 (RA 17 57 06 Dec 37 05 00) and tell me what you see. That’s right! Nothing. This is dark nebula B 288 – a cloud of dark, obscuring dust which blocks incoming starlight. Look carefully at the stars you can see and you’ll notice they appear quite red. Thanks to B 288, much of their emitted light is absorbed by this region, providing us with a pretty incredible on-the-edge view of something you can’t see – a Barnard dark nebula.

Now let’s have a look at some things gravitationally bound as we start at Eta Lupi – the “n” symbol on our map. Eta is a fine double star which can even be resolved with binoculars. Look for the 3rd magnitude primary and 8th magnitude secondary separated by a wide 15″. You’ll find it by starting at Antares and heading due south two binocular fields to center on bright H and N Scorpii – then one binocular field southwest (RA 16 00 07 Dec 38 23 48).

When you are done, hop another roughly five degrees southeast (RA 16 25 18 Dec 40 39 00) to encounter the fine open cluster NGC 6124. Discovered by Lacaille and known to him as object I.8, this 5th magnitude open cluster is also known as Dunlop 514, as well as Melotte 145 and Collinder 301. Situated about 19 light-years away, it will show as a fine, round, faint spray of stars to binoculars and be resolved into about 100 stellar members to larger telescopes. While NGC 6124 is on the low side for northern observers, it’s worth the wait for it to hit its best position. Be sure to mark your notes, because this delightful galactic cluster is a Caldwell object and a southern skies binocular reward!

Source: Wikipedia
Chart courtesy of Your Sky.

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Libra is a constellation of the zodiac, positioned on the ecliptic plane between between Virgo to the west and Scorpius to the east. It is a faint group of stars and not easy to recognize. Its two major stars once once represented the claws of Scorpius. How and when it came to be recognized by its present designation is unknown. Libra covers approximately 538 square degrees of sky and contains 6 stars in its asterism. There are 46 Bayer Flamsteed designated stars within Libra and it is bordered by Serpens Caput, Virgo, Hydra, Centaurus, Lupus, Scorpius and Ophiuchus. Libra can be seen by all observers at latitudes between +65° and ?90° and is best seen at culmination during the month of June.

In mythology, the Alpha and Beta stars of Libra once represented Chelae Scorpionis, the northern and southern claws of the Scorpion. Who knows exactly where and when it became depicted as a set of scales, but the Romans identified it with the scales held by Astraea, the goddess of justice. They believed the Moon was in Libra when Rome was founded and the astrological sign represented balance because this is where the Sun was housed during autumnal equinox. Oddly enough, Libra is the only astrological symbol that doesn’t depict some type of living creature.

Once you’ve located it, let’s take a binocular tour of Libra, beginning with Alpha Librae – Zubenelgenubi – the “a” symbol on our map. Despite its alpha designation, it’s not the brightest star here, but what you’ll find here is a wonderful, visual double star. Alpha Librae “The Southern Claw” is located approximately 77 light years from the Sun, and the components are easily separated with even the slightest visual aid. Look for a beautiful yellow coloration to the spectral type A3 primary star and a slight blue tinge to the far fainter type F4 companion. Zubenelgenubi is close to the ecliptic so it can be easily occulted by the Moon!

Now, hop to Beta Librae – Zubeneschamali – the “B” symbol on our map. “The Northern Claw” is actually the brightest star in Libra and also one of the furthest away at about 160 light years from Earth. Beta Librae is a blue dwarf star of spectral type B8, what would appear to be a rather ordinary main sequence star – but take a really close look in binoculars. Does it appear a little green to you? Zubeneschamali is running a high temperature – more than twice that of our own Sun – produces light with a simple spectrum. This makes it a perfect candidate for examining interstellar gas and dust which lay between us and it – but its rapid hydrogen fusion also causes it to appear a little more green than other stars. A color rarely seen in stars! What’s more, Beta Librae spins about 100 times faster than our Sun and shines about 130 brighter. Not bad for a star that not even as evolved as Sirius!

Point your binoculars further south for Sigma Librae – the “O” symbol with the little flag on our map. Its traditional name is Zubenhakrabi – a cool class M (M3) rather-luminous red giant. Located approximately 292 light years from our solar system, Sigma is rather special – a prototype of its own group of ultra-small-amplitude variables which are called Sigma Librae variable stars. What are they? Pulsing red giants, of course! It doesn’t change its brightness much, maybe only 0.16 magnitudes over a 20-day period, but knowing you’re looking at dying solar mass star, with a dead helium core, fueled by internal nuclear-burning shells of helium and hydrogen is still undeniably fascinating! What’s Zubenhakrabi future like? Chances are it will just eventually become a Mira-type variable star that will eventually shed its outer skin, leaving its now-content carbon-oxygen center to become just another of the white dwarf stars of the night!

Time to get out the telescope and head for NGC 5694 (RA 14:39:36.5 Dec -26:32:18). This 10th magnitude, irregularly shaped globular cluster was discovered by Sir William Herschel in 1784 and is one of the more remote globular clusters of the Milky Way Galaxy at a distance of about 113 thousand light years. If you find it difficult to resolve, you’d be right. Its brightest stars average about magnitude 16 and so far none of them have been discovered to be variable. Why bother if it is so dim? Because this globular cluster is a curiosity! It’s moving… and it’s moving fast. According to studies, NGC 5694 can either be a hyperbolic orbit or may be elevated into a higher energy orbit during its evolution. It is possible that NGC 5694 may have once belonged to the Magellanic Clouds. Thanks to work done by Lee (et al) who discovered one red giant star, we know that it has a “unique chemical abundance pattern” and an “an extragalactic origin”. No wonder it’s so faint….

Need a big telescope challenge? Then try NGC5792 (RA 14:58.4 Dec -01:05). At around magnitude 12, it’s going to take some dark sky to catch this nearly edge-on spiral galaxy, but it is worth your time and trouble. As part of the Herschel catalog, you’ll find a distracting star on the western edge, but very pretty spiral galaxy structure with a bright nucleus await you. At 85 million light years away, it still shows some very nice form to large aperture.

Before you put away your telescope, try NGC 5903/5898 (RA 15:18.6 Dec -24:04). This binary elliptical galaxy pair is quite achievable in an 8″ telescope with dark skies and good seeing conditions. You’ll find them about three degrees northeast of Sigma, and just north of a pair of 7th magnitude stars. While northernmost NGC 5903 seems to be nothing more than a faint elliptical with a brighter concentration toward the center and an almost identical elliptical – NGC 5898 – to the southwest, you’re probably asking yourself… Why the big deal over two small ellipticals? First off, NGC 5903 is Herschel III.139 and NGC 5898 is Herschel III.138…two more to add to your studies. And second? The Very Large Array has studied this galaxy pair in the spectral lines of neutral hydrogen. The brighter of the pair, NGC 5898, shows evidence of ionized gas which has been collected from outside its galactic realm – while NGC 5903 seems to be running streamers of material toward its neighbor. A double-galaxy, double-accretion event! But there’s more… Look to the southeast and you’ll double your pleasure and double your fun as you discover two double stars instead of just one! Sometimes we overlook field stars for reasons of study – but don’t do it tonight. Even mid-sized telescopes can easily reveal this twin pair of galaxies sharing “their stuff,” as well as a pair of double stars in the same low power field of view. (Psst…slim and dim MCG 043607 and quasar 1514-241 are also here!) Ain’t it grand?

Tip the “scales” in your favor if you have a big telescope and get a good star chart. There’s lots more in Libra than you think!

Source: Wikipedia
Star Chart Courtesy of Your Sky.

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For all the things different about Neptune from Earth, here’s something that’s remarkably similar. The tilt of Neptune’s axis is 28.32 degrees. Compare that to the Earth’s tilt of 23.5 degrees.

With such a similar axial tilt, Neptune has very similar seasonal variations to Earth. For half of its orbit around the Sun, Neptune’s northern pole is tilted towards the Earth, and then for the other half of its orbit, the southern pole faces the Sun.

One of the biggest effects of the seasonal variation on Neptune is the current “hotspot” at Neptune’s southern pole. While most of Neptune has an average temperature of around -200 Celsius, Neptune’s south pole is about 10 degrees warmer. This makes the south pole warm enough so that methane gas – frozen in the rest of Neptune’s atmosphere – can escape into space.

Once Neptune’s seasons reverse, the hotspot will shift back to Neptune’s north pole.

We have written many stories about Neptune for Universe Today. Here’s an article about how there could be oceans deep down within Neptune’s interior, and some movies of Neptune captured by Hubble.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

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We know there’s life on Earth, but could there be live on Neptune? And if there is life on Neptune, what kind of life is it?

Wherever we find liquid water on Earth, we find life. Whether that water is thousands of meters beneath the ground, inside nuclear reactors, or inside glaciers. As long as there’s water, there’s life. Of course, it’s just microbial life – but still, life.

To find life on Neptune, the planet would need to have a source of energy that bacterial life can exploit, as well as a standing source of liquid water. At its surface, the temperature of Neptune dips down to 55 Kelvin. That’s very cold, and there’s no way liquid water could exist.

But as you travel down into Neptune’s interior, temperatures and pressures increase. And there could very well be a point inside the planet where water remains as a liquid, and life could exist inside it. Of course, this region would be hundreds of kilometers below the surface, and would be impossible for us to study. So for now, it will have to remain a mystery.

Right now, scientists don’t know if there’s any life on Neptune, and the conditions on the planet seem very hostile for life. It’s unlikely we’ll ever find any there.

We wrote a detailed article on Universe Today about the possibility that there are oceans inside Neptune and other gas giant planets.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

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The mass of Neptune is 1.02×10²⁶ kg.

That’s a pretty big number. If you wrote it out, it would be 102,000,000,000,000,000,000,000,000 kg. That’s still hard to wrap your brain around, so let’s give you some context. The mass of the Earth is 6 x 10²⁴ kg. In other words, the mass of Neptune is 17 times the mass of the Earth.

Neptune is actually more massive than Uranus. Uranus has only 14.5 times the mass of Earth, while Neptune has 17 times the mass of Earth.

Of course, the mass of Neptune is pretty tiny compared to some of the more massive objects in the Solar System. Neptune has only 5% the mass of Jupiter, and you could have 19,400 Neptunes to match the mass of the Sun.

We have written many stories about Neptune on Universe Today. Here’s an article about how it might have used its mass to capture Triton.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

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Neptune is a gas planet, so it doesn’t have a solid surface. If you tried to walk on the surface of Neptune, you’d sink right in. But let’s say you could walk on Neptune. How strong is the gravity on Neptune? How heavy would you feel?

The surface gravity of Neptune is 1.14 times the gravity on Earth. In other words, if you could actually walk on Neptune, you would feel only a little heavier than if you were walking on Earth. If you weighed 100 kg on Earth, you would weight 114 kg on Neptune. Compare that to the much lower gravity you would feel on the Moon (16.5%) or Mars (37.6%).

Neptune has much more mass than Earth. In fact, it has a mass of 17 times the mass of the Earth. You would think that would make the gravity much more extreme. But it also has a much larger size. The diameter of Neptune is 3.8 times the diameter of Earth. This brings the gravity on Neptune down to a very comfortable 114% the gravity of Earth.

Except for the non-solid part, walking on Neptune would feel very comfortable.

Want to learn more about the gravity on the Moon, or the gravity on Mars?

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.

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The density of Neptune is 1.638 g/cm³.

Just to give you some comparison, the density of water is 1 g/sm³. In other words, if you had a bathtub big enough, Neptune would sink into it. This is different for Saturn which has a density of less than 1. While Neptune sinks, Saturn would float. Of course, both planets are much less dense than Earth, with a density of 5.51 g/cm³.

Want to calculate the density of Neptune on your own? It’s pretty simple math. Just take the mass of Neptune, and divide it by its volume.

The mass of Neptune is 1.0243×10²⁶ kg, and the volume of Neptune is 6.254×10¹³ km³. Divide the two, and convert to grams per cubic centimeter, and you’ll get the density of Neptune: 1.638 g/cm³.

We have written many stories about Neptune on Universe Today. Here’s an article about how there might be liquid oceans deep within Neptune. And here’s an article with cool videos of Neptune captured by Hubble.

If you’d like more information on Neptune, take a look at Hubblesite’s News Releases about Neptune, and here’s a link to NASA’s Solar System Exploration Guide to Neptune.

We have recorded an entire episode of Astronomy Cast just about Neptune. You can listen to it here, Episode 63: Neptune.