Category: Guide to Space

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The constellation of Hydrus was originally created by Petrus Plancius from the observations of Dutch sea navigators Pieter Dirkszoon Keyser and Frederick de Houtman when exploring the southern hemisphere and should not be confused with its more northerly counterpart – Hydra. Hydruss’ stellar patterns became known when it appeared on a celestial globe in 1597 and was considered a constellation when it was added to Johann Bayer’s Uranometria catalog in 1603. It survived the years to become one of the 88 modern constellations recognized by the International Astronomical Union. Hydrus is a southern circumpolar constellation and covers approximately 243 square degrees of sky. It contains 3 major stars which make up its asterism and 19 stars which have Bayer/Flamsteed designations. Hydrus is bordered by the constellations of Dorado, Eridanus, Horologium, Mensa, Octans, Phoenix, Reticulum and Tucana. It can be seen by observers located at at latitudes between +8° and ?90° and is best visible at culmination during the month of November.

Because Hydrus wasn’t visible to the ancient Greeks or Romans, no mythology surrounds this constellation. It is, however, just another example of how constellation names and figures can sometimes repeat themselves, like Ursa Major and Minor, Canis Major and Minor, Pegasus and Equuleus, Leo and Lynx… Perhaps the ancient Maori had legends about this handful of stars! To them, the Hydrus was the water snake who killed crocodiles by entering into their mouths and killing them from the inside…

Let’s begin our binocular tour with the second brightest of the stars – Alpha Hydri – the “a” symbol on our map. Once upon a time in the year 2900 BC, this happy little F class dwarf star had the honor of being the southern pole star. Thanks to the precession of the equinoxes, it has long since moved away, but continues to be of interest as it gears up to become a red giant star. Rotating completely on its axis about every 26 hours, all of Alpha’s exterior activity happens acoustically rather than magnetically. Why? Because 71 light year distant Alpha has a high metal content!

Now, drop south for Beta Hydri – the “B” symbol on our map. In binoculars you’ll see a nice visual double star. Beta is located 24.4 light years from our solar system and right now serves the distinction of being the brightest star closest to the south celestial pole. What’s special about it? What you’re looking at is nearly a duplicate of our own Sun. While it is just slightly larger and brighter, Beta is most definitely a subgiant near or at the end of its hydrogen fusing life – on its way to becoming a red giant no larger than the orbit of Earth. Its maximum rotation period is 29 days, very near to that of the 24 day cycle of Sol and its evolutionary fate appears to be similar – a “one day” white dwarf star.

Hop north and east for Gamma Hydri – the “Y” shape on our map. If you think you’re seeing red compared the the soft yellow-white of the other stars – you’re right. Gamma is a luminous class M red giant star that has signed off core hydrogen fusion and is approaching the end of its life span. While it is not terribly large – not even the size of the orbit of Mercury compared to our Sun, Gamma puts out some real stellar luminosity – shining 650 times brighter than Sol. This may be because it is firing up its helium to fuse carbon and oxygen… or it may have depleted its helium and is about to toss off its outer envelope and become a dead, white dwarf!

Before we move on, let’s head back north… Stopping first to pay our respects to visual double star Pi 1 Hydri – a non-interacting pair of 6th magnitude giants. Look closely because Pi 1 is red and Pi 2 is orange! Now, hop east to Eta 2 – the “n 2” symbol on our map. What’s so special about Eta 2? First off, Eta Hydri is a double star – a true binary star consisting of a blue-white dwarf called Eta 1 and a yellow giant star, Eta 2. But hey, that’s not what really fun. What’s really run is there is a giant planet orbiting around Eta 2! It’s about 217 light years from Earth and it goes by the very unromantic name of HD 11977 b. Sure, it’s about six and a half times the size of Jupiter, which puts it right up there at dead star size… But hey! It’s a planet! This means at least a few intermediate-mass stars could host substellar companions – either planets or brown dwarfs. When later measured by Doppler, science proved HD 11977 b was clearly within the planetary mass and became the first to be accurately determined.

Are you ready for a true telescope challenge? Hydra isn’t precisely known for bright objects, so our first is IC 1717 (RA 01h 32m 30.0s Dec -67 32′ 12.0″). What is it? Well… nothing. The only thing we really know for sure it that something was there when Dreyer cataloged this position because Dreyer was exceedingly good at his job. Maybe it was a comet… Maybe it was something variable. It never hurts to look!

Just in case you have an small telescope, you might want to try NGC 1466 (RA 03:44.5 Dec -71:41). This 11.5 magnitude globular cluster doesn’t belong to the Milky Way Galaxy… it belongs to the Large Magellanic Cloud. Even that far away, science has been able to spot that it has 44 RR Lyra type variable stars and is every bit as old as the galaxy halo to which it belongs!

For large telescopes, try NGC 1511 (RA 3:59.5 Dec -67:38), too. This ‘object’ is actually a triple set of galaxies whose co-ordinates are so close to one another that they almost appear as one unit. Interacting galaxies? You bet. This galaxy collision is a process that’s been going on for a billion years and will eventually become a giant elliptical galaxy at then end. Chances are NGC 1511 has already absorbed at least one galaxy in its past. According to scientists, “the peculiar optical ridge to the east of NGC 1511 is probably the stellar remnant of a galaxy completely disrupted by interactions with NGC 1511”.

Sources: Wikipedia, Chandra Observatory
Charts Courtesy of Your Sky.

The sprawling constellation of Hydra was one of the 48 constellations listed by Ptolemy and endures today to be the largest of the 88 modern constellations adopted by the International Astronomical Union. Spanning an incredible 1303 square degrees of night sky and containing 17 primary stars in the asterism, Hydra contain 75 stars with Bayer/Flamsteed designations. It is bordered by the constellations of Antlia, Cancer, Canis Minor, Centaurus, Corvus, Crater, Leo, Libra, Lupus, Monoceros, Puppis, Pyxis, Sextans and Virgo. Position south of the ecliptic plane, Hydra is visible to all observers at latitudes between +54° and ?83° and is best seen at culmination during the month of April.

In mythology, Hydra represents the Snake – not much of a stretch of the imagination given all the twists, turns and distance this constellation takes across the sky. According to legend, Apollo sent the Raven, Corvus, off with the Cup (Crater) to fetch a drink. When the Raven spent his time waiting for a fig to ripen instead of returning with Apollo’s refreshment, he realized he’d made a mistake and grabbed a water snake to offer to the sky god as atonement for his tardiness. Infuriated, Apollo tossed the whole lot of them into the sky where they remain until this day… Some legends also refer to Hydra as one of the many labors of Hercules, too!

Shall we begin with a binocular tour of Hydra? Then let’s start first with the small asterism of stars which marks the “head” of Hydra located between bright stars Regulus and Procyon. When you’ve picked out this distorted circlet, focus your attention on the northernmost of these stars – Epsilon – the backward “3” on our map. While to binoculars it might seem rather ordinary, Epsilon is actually a fantastic multiple star system with at least five members! The primary is a yellow-white giant star with a white subgiant star orbiting so close that it is considered a spectroscopic binary star. A bit further away is another binary pair, the G and F star… and further away yet is a class M dwarf star. Be sure to take out your telescope and have a look….

Now move southeast for the brightest star in Hydra – Alpha – the “a” symbol on our map. Its name is Alphard and it is located about 175 light years away from Earth. Shining in a very soft orange color, this giant star reaches temperatures of about 4000 degrees Kelvin and if at home in our solar system would be about 400 times brighter than our Sun. What makes Alphard unique? Its barium content. At one time Alphard, too, was a binary star, but its massive companion is long gone. Alphard happily collected its by-products of nuclear fusion and left us with evidence of what once was!

Keep your binoculars handy and use the two points of reference you’ve just learned to find our next target – Messier 48. By connecting Epsilon and Alpha as the base of an imaginary triangle with the top pointed southwest, aim your binoculars at the apex and behold one very nice – and very bright – open star cluster. Discovered by Charles Messier in 1771 and also cataloged as NGC 2548, you might even be able to distinguish this stellar field as a hazy spot unaided from a dark sky location. With an estimated age of about 300 million years, you’ll see a very large group of about 50 stars which can resolve into as many as 80 members in larger telescopes. When you see M48, you can thank Caroline Herschel for fixing Messier’s position mistake on this one!

Hop along to Lambda Hydrae – the upside down “Y” on our map. Lambda is a visual double star in binoculars, but it is also a true spectroscopic binary star as well. As you continue south, then east and pass by Xi (the squiggle), keep in mind Xi is unique, too. Xi is an evolved giant star with solar-like oscillations… the very first time science has proved the existence of vibrations in a giant star 10 times the size of our Sun! If you place Xi to the western edge of the field in binoculars, you’ll also see 5th magnitude Beta Hydrae, too. Seeing two there instead of one? You should. Beta is a visual double star and the pair are only separated by about half a magnitude.

Now head northeast towards Gamma, but stop by Messier 68 along the way. This class X globular cluster was discovered by Charles Messier on April 9, 1780, but was resolved into stars by Sir William Herschel who said; “A beautiful cluster of stars, extremely rich, and so compressed that most of the stars are blended together; it is near 3′ broad and about 4′ long, but chiefly round, and there are very few scattered stars about.” M68 will look like a small, round fuzzy in binoculars, but larger telescopes will resolve this 33,000 light-year distant Milky Way resident out!

Are you ready for Gamma Hydrae? It’s the “Y” shape on our map. If you got lost, just use the lower two stars of Corvus to point east towards it. Gamma is located about 132 light years away from our solar system and shines approximately 105 times brighter than Sol. In the not-to-distant past, Gamma decided to shut down its hydrogen fusion factory, which means it may possess a dead helium core. What’s in Gamma’s future? Chances are it will grow larger and less luminous as the core shrinks – then it will fire up to fuse carbon and oxygen. When it does it will become six times brighter and five times bigger! If you’re looking with a telescope and see another star there, you’re right… but it’s an optical companion.

To the east of Gamma is R Hydrae. Now here is one classy variable star! Located about 2000 years away from Earth, R Hydrae’s changes take a period of 389 days to happen, but they happen in a big way. The magnitude of this crazy star jumps from a very dim and telescopic only 11.0 to an easy unaided eye 3.2! R is the third Mira-type variable discovered and may have been noted as early as 1662 by Johannes Hevelius. R Hydra is also special because it has a “declining period” – it has changed its times by 100 days in the last couple of hundred years. So what’s happening? A helium shell is building up around the exterior – just waiting for the day to reach a critical mass and ignite, creating more carbon and oxygen. This is called a “helium shell flash” and it signals the end of life for the giant star. Eventually the layers will just expand into space and the carbon-oxygen core will shine as a white dwarf star. Look around while you’re there… Because you just might spot a companion!

Now drop almost due south for Messier 83 (RA 13:37.0 Dec -29:52). In binoculars this superb spiral galaxy will appear as a soft round glow, but telescopes will reveal wonderful spiral galaxy structure (dependent on observer latitude). With a classification somewhere between a normal and barred spiral galaxy, large telescopes can expect to at least see three traces of spiral arm structure. For astrophotographers, you’ll find terrific star forming regions will appear and dark dust lanes follow the spiral structure throughout the disk.

Ready to do a telescope object in Hydra? Then look no further than NGC 3242 (RA 10:24.8 Dec -18:38). This 8th magnitude planetary nebula is best known as the “Ghost of Jupiter” for its magnificent size! Be sure to look for a double halo structure and the 11th magnitude central star. Even small telescopes will catch a faint blue color to this superb object!

For larger telescopes, let’s try some galaxies. First off, NGC 3621 (RA 11:18.3 Dec -32:49) located about about 3 degrees west/southwest of Xi. You’ll find this fairly larger and bright spiral galaxy sitting inside a box of faint stars! Need a pair of galaxies? Then try NGC 3923 and NGC 3904 (RA 11 h 51 min Dec – 28 48′). Use low magnification and a wide field eyepiece to capture this spiral and elliptical galaxy in the same view.

There’s plenty more deep sky in the constellation of Hydra to be explored, so be sure to get a good star chart and charm the “Snake”!

Sources: Chandra Observatory, Wikipedia
Charts Courtesy of Your Sky.

If you’ve got a clear view of the skies, and happen ti live in the southern hemisphere, there’s a relatively obscure constellation you should probably check out. It’s known as Horologium, a region of the sky that is named after an important historic personality, one who is largely responsible for how we measure time.

The constellation of Horologium was one of 14 created by Nicolas Louis de Lacaille to chart southern hemisphere skies. Originally named “Horologium Oscillitorium” to honor Christiaan Huygens – the inventor of the pendulum clock – it was later shortened to its present named when adopted as one of the 88 modern constellations by the IAU.

Horologium spans 249 square degrees of sky and consists of 6 mains stars in the asterism, with 10 Bayer/Flamsteed designated stars. It is bordered by the constellations of Eridanus, Hydrus, Reticulum, Dorado and Caelum. Horologium is visible to all observers at latitudes between +30° and ?90° and is best seen at culmination during the month of December.

Horologium was named to honor Christiaan Huygens, the Dutch mathematician, astronomer and physicist. While traveling in the southern hemisphere and charting the heavens, Nicholas de Lacaille (who loved all things science) found this dim constellation reminded him of Huygen’s newly invented pendulum clock.

Huygens clock incorporated the first harmonic oscillator – increasing the accuracy to within 15 seconds per day. His “horological innovation” so impressed Lacaille that he found the pattern for this invention in the stars.

Horologium is bordered by five different constellations: Eridanus (the Po River), Caelum (the chisel), Reticulum (the reticle), Dorado (the dolphinfish/swordfish), and Hydrus (the male water snake).

Spring driven pendulum clock, designed by Christiaan Huygens (1657) and copy of the Horologium Oscillatorium,  Museum Boerhaave, Leiden. Credit: Flickr/Rob Koopman

The official constellation boundaries are defined by a twenty-two sided polygon. Covering a total of 249 square degrees, Horologium ranks 58th in area out of the 88 modern constellations.

With almost no bright stars to claim, stargazing at Horologium can be a bit tricky. But with binoculars, a telescope, and a chart, there are plenty of opportunities for some picturesque views. Let’s start by taking a look in binoculars with Alpha Horologii – the “a” symbol on our map.

Located about 193 light years from Earth, this very normal K1 orange giant star – quietly fusing its core helium into carbon and oxygen. Nearby is Delta, the “8” symbol. It, too is rather ordinary. Delta is a spectroscopic binary star, located about 175 light years away.

So, with very little in the constellation in the way of stars, what is there to do with a telescope? First of all, there’s NGC 1261 (RA: 03:12:15.3; Dec: -55:13:01). This 8th magnitude globular cluster is very well condensed and is at home in a very picturesque field. Small wonder it made the Caldwell list at number 87. Look for a very bright core region and well resolved chains of stars at the edges of this pretty star cluster.

For larger telescopes, try NGC 1512 (RA 4:03.9 Dec -43:21). At slightly brighter than magnitude 11, this barred spiral galaxy belongs to the Dorado group and is located about 30 million light years away. While you won’t find much details here, NASA’s Galaxy Evolution Explorer show spiral galaxy NGC 1512 sitting slightly northwest of elliptical galaxy NGC 1510.

The two galaxies are currently separated by a mere 68,000 light-years, leading many astronomers to suspect that a close encounter is currently in progress. The overlapping of two tightly wound spiral arm segments makes up the light blue inner ring of NGC 1512. Meanwhile, the galaxy’s outer spiral arm is being distorted by strong gravitational interactions with NGC 1510.

Another challenge? Then try NGC 1433 (RA 3:42.0 Dec -47:13). This magnitude 10 galaxy is an example of a ringed barred spiral. While physically you may only notice a bright nucleus and the soft bar, the stars orbiting the disk of this galaxy shows its internal motions photographically. A small elliptical ring can develop near the nucleus – blue proof of star formation. Always keep a watch, because this galaxy had a supernova event in 1985.

Source: Wikipedia
Chart Courtesy of Your Sky.

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The constellation of Hercules belongs to one of the 48 originals plotted by Ptolemy and has survived time to become one of the 88 modern constellations adopted by the International Astronomical Union. Spanning an impressing 1225 square degrees of sky and containing 22 stars in the asterism, it has 106 Bayer/Flamsteed designated stellar designations. Hercules is bordered by the constellations of Draco, Bootes, Corona Borealis, Serpens Caput, Ophiuchus, Aquila, Sagitta, Vulpecula and Lyra. It is visible to all observers at latitudes between +90° and ?50° and is best seen at culmination during the month of July. There is one annual meteor shower associated with Hercules, the Tau Herculids, which peak on or near June 3. The radiant, or point of origin, is near the Hercules/Corona Borealis border and the meteor shower itself last about a month beginning around two weeks before and lasting about two weeks after the peak date. Most of these meteors are quite faint and at maximum, expect to see no more than 15 per hour average.

The mythology surrounding Hercules is a long and very colorful one. He was considered the greatest of all heroes – both Greek and Roman. The legendary strong man was supposed to be the son of Zeus; immortal, yet forever challenged by Hera by his circumstance of birth. His tasks were many: killing a lion with a hide that could not be punctured, destroying the many headed Hydra, cleaning out nasty stables, fighting birds with knife-like feathers, capturing a bull that breathed fire, taming horses that ate flesh, stealing cattle from monsters, stealing golden apples, fighting dragons, snatching a three-headed dog, loosing the love of his life, accidentally killing his teacher and so much more… It is no wonder that Hercules is so often depicted as kneeling in the sky! Even an immortal would be tired from so much… But at last, Hercules earned his place in the stars and he remains there to this day… The fifth largest constellation in the night sky.

Because the constellation of Hercules has no particularly bright stars, it is sometimes difficult to navigate through with binoculars until you learn a few “key” ingredients. There is a large asterism which is fairly easy to recognize that forms a lopsided box, referred to as the “keystone”. The northeast corner is Pi. The northwest corner is Eta. The southeast corner is Epsilon. The southwest corner is Zeta. Always remember when you look at a star chart that north and south are up and down… But east is to the left and west is to the right! To find the “keystone”, let bright Vega guide you…. just start by looking southwest.

Have you found Pi Herculis, yet? If you’re seeing two stars in your binoculars and you’re not sure which one, Pi is the slightly redder and slightly brighter of the pair. Situated about 370 light years from Earth, Pi Herculis is a cool, red supergiant star that was born about 140 million years ago. Although you can’t see it, Pi also has an orbiting substellar companion about 27 times larger than Jupiter there, too! Now, drop south for Epsilon – another binary star. Chances are good this pair of twin stars are almost identical to each other – about twice the size and mass of our Sun – and orbit each other so closely they nearly touch.

Don’t stop moving south. Our next stop is Gamma Herculis, the “8” shape on our map. Gamma is also a very cool star – one with a dead helium core that’s waiting to become a red giant. In maybe 8 million or so years, it will begin to fuse helium into carbon and become much brighter than it is tonight. If you see a faint companion star, it is only an optical one in binoculars – but Gamma is also a genuine binary star.

Next stop? Further south for Alpha – the “a” shape on our map. Now here is a great star! Named Rasalgethi and located about 380 light years away, here we have one of the finest double stars in the night sky. The primary star is a magnificent red class M supergiant that’s over 475 more luminous than our Sun and whose size would fill up our solar system clear out to the orbit of the asteroid belt. But that’s not all… Aim a telescope at Rasalgethi and you’ll see it has a fifth magnitude companion five seconds of arc away. It is also a binary star – an F2 giant with a close orbiting dwarf star companion. Surrounding this whole system is an envelope of gas expelled from the primary star’s incredible solar winds… Enjoy the unusual red and green hues of this colorful double star! And keep watching… Because Rasalgethi is also an irregular variable star – whose brightness changes from magnitude 2.7 to 4.0 within a period of about three months.

Next up? Return to the “keystone” and the northwest corner for Eta – the “n” shape on our map. Shining away about 50 times brighter than our own Sun at a distance of 112 light years, there is nothing particularly impressive about Eta, except where it leads. Begin moving your optics slowly south towards Zeta and you will encounter the “Great Hercules Cluster” – M13! Easily seen in binoculars, sometimes visible to the unaided eye in a dark sky location and absolutely magnificent in any telescope, Messier 13 is perhaps the most famous of all northern globular clusters. Located about 25,000 light years away and home to more than half a million stars, this 12 billion year old system spans no more than 100 light years across. Also known as NGC 6205, this impressive ball of stars was first discovered by Edmund Halley in 1714 and catalogued by Charles Messier on June 1, 1764. If you aren’t impressed, then take the words of Kurt Vonnegut to heart: “”Every passing hour brings the Solar System forty-three thousand miles closer to Globular Cluster M13 in Hercules — and still there are some misfits who insist that there is no such thing as progress.”

Ready for more? Then take another look at Eta and Pi and form an imaginary triangle on the sky using these two stars as the base. The apex is very near where you will find another amazing globular cluster for binoculars or small telescopes – Messier 92. First discovered by Johann Elert Bode in 1777 and independently rediscovered by Charles Messier on March 18, 1781, M92 is a 16 billion year old beauty – formed back at the Milky Way Galaxy’s beginnings. Hiding in there are 16 variable stars and one rare eclipsing binary. What a treat to have two such bright objects so near to one another!

Ready for an alternative binocular tour of Hercules? Then let’s use what you’ve learned. Start by locating magnificent M13 and move 3 degrees northwest – about a binocular field. What you will find is a splendid loose open cluster of stars known as Dolidze/Dzimselejsvili (DoDz) 5 – and it looks much like a miniature of the constellation Hercules. Just slightly more than 4 degrees to its east and just about a degree south of Eta Herculis is DoDz 6, which contains a perfect diamond pattern and an asterism of brighter stars resembling the constellation of Sagitta. Now we’re going to move across the constellation of Hercules towards Lyra. East of the “keystone” is a tight configuration of three stars – Omicron, Nu, and Xi. About the same distance separating these stars northeast you will find DoDz 9. You’ll see a pretty open cluster of around two dozen mixed magnitude stars. Now look again at the “keystone” and identify Lambda and Delta to the south. About midway between them and slightly southeast you will discover the stellar field of DoDz 8. This last is easy – all you need to do is return to Alpha. Move about 1 degree northwest (Rasalgethi will stay in the field) to discover the star-studded open cluster DoDz 7. These great open clusters are very much off the beaten path and will add a new dimension to binocular and fast-telescope observing!

Would you like a challenge? Then go back to M13 with a large telescope and take a look about 40 arc minutes to the northeast for NGC 6207 (RA 16:43.1 Dec +36:50). At near magnitude 12, this small spiral galaxy isn’t for everyone, but it’s always a smile a bonus when you’re in the area, despite the lack of details. Try NGC 6210 (RA 16:44.5 Dec +23:49), too. This bright planetary nebula is suited for all telescopes and takes magnification very well. Look for a blue/green color in larger telescopes, and adding a nebula filter can sometimes reveal some subtle details of a shell around this one. But be sure to take the filter out if you want to catch the central star!

Sources: Chandra Observatory, SEDS
Chart Courtesy of My Sky.

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The constellation of Grus was originally created by Petrus Plancius from the observations of Dutch sea navigators Pieter Dirkszoon Keyser and Frederick de Houtman when exploring the southern hemisphere. Grus’ stellar patterns became known when it appeared on a celestial globe in 1597 and was considered a constellation when it was added to Johann Bayer’s Uranometria catalog in 1603. It survived the years to become one of the 88 modern constellations recognized by the International Astronomical Union. Grus is located south of the ecliptic plane and covers approximately 366 square degrees of sky. It is bordered by the constellations of Piscis Austrinus, Microscopium, Indus, Tucana, Phoenix and Sculptor. The asterism consists of 7 main stars and there are 28 stars with Bayer/Flamsteed designations. Grus is visible to all observers at latitudes between +34° and ?34° and is best seen at culmination during the month of October.

Until the late 16th century, Grus was considered part of Piscis Austrinus – the “Southern Fish” – since most of its stars weren’t visible to northern latitudes. When exploration began below the equator many wondrous new creatures were discovered. One such bird was the fishing crane – Phoenicopterus – the flamingo. Perhaps this is how the constellation got is name, since Grus is also Dutch for “crane”!

First let’s take a binocular tour of Grus, starting with its brightest star, Alpha, the “a” symbol on our map. Alpha Gruis proper name is Alnair, the Arabic word for “bright one of the tail”. In this case, it was originally the tail of the fish. But besides being a bit “fishy”, Alnair is a hot, blue subgiant giant star about 101 light years away from Earth. Not only is it larger, hotter and brighter than our own Sol, but it a rather fast stellar rotation – making a complete rotation in under a day. Hop on to Beta Gruis, the “B” symbol on our map. Beta Gruis is a rare kind of star – a cooler class M giant star. It is very possible it is in an advanced state of evolution, losing mass and brightening with a dead carbon-oxygen core in preparation for sloughing its outer envelope – ready to become a Cepheid variable!

Now for visual and binocular double star, Delta 1 and Delta 2 Gruis – the “8” symbol in the center of the constellation. While this pair aren’t physically connect to one another, they do make a pleasing sight with their lovely yellow and red contrasting colors. For a true telescopic binary star, hop north to Upsilon. This disparate pair is separated by over a degree of arc and the difference between stellar magnitudes is a great experience.

For the telescope, tackle NGC 7213 (RA 22:09.3 Dec -47:10) about 16′ southeast of Alpha. This 10th magnitude Seyfert galaxy has definitely got some stories to tell. Not only is it a spiral galaxy, but one that has an incredible,giant H-alpha filament erupting from its nucleus. Another great challenge is NGC 7582, 7590 and 7599 (RA 023:19 Dec -42:3). Here is a small galaxy group consisting of three faint spirals in the same field, all tilted close to edge on. While at least an intermediate sized telescope is need to see them, a wide field eyepiece will place all three in the same field of view at around 100x magnification. Before we leave for the night, let’s try NGC 7410 (22:55.0 -39:40). This uniformly illuminated tilted spiral galaxy shows little sign of structure, despite its bright nature.

Sources: Wikipedia, SEDS
Chart courtesy of Your Sky.

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A lunar year or lunar calendar is one that is based on the cycles of the moon phases. The problem with a lunar calendar is that it drifts away from the seasons. Each year, the start and end dates of each month drift by 11 days. In order to stay correct, every lunar calendar has to deal with this drift away from the calendar year.

Let’s examine a year. A lunar month lasts 29.53 days. So after 12 lunar months, you’re about about 354 days. This is short of the 365 days that it takes the Earth to orbit the Sun. This is a problem since after about 3 years, the lunar months are out of cycle with the solar year by about a month. And this problem would just continue.

To make the lunar calendar work in China, farmers would add in a leap month every 3 years. This would mostly get the lunar month to line up with the solar year, but they still drifted apart somewhat. For some calendars used for religious purposes, such as the Islamic Hirji calendar, they never bothered to sync up the calendars and let them drift. It takes 33 years for the cycle of lunar years to get back to the original position.

A lunar calendar was used in England up until Tudor times.

Want more information about the Moon? Here’s NASA’s Lunar and Planetary Science page. And here’s NASA’s Solar System Exploration Guide.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

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The density of the Moon is 3.346 g/cm³. The Moon is actually the second densest moon in the Solar System after Io.

Need some comparisons? The density of Earth is 5.52 g/cm³. This makes it the densest planet in the Solar System. The density of Io is 3.53 g/cm³.

Astronomers believe that the Moon formed when a Mars-sized object crashed into the Earth. The resulting debris from the collision collected into orbit around the Earth and became the Moon. The Moon’s relatively low density comes from the fact that it was mostly the Earth’s upper mantle and crust that was thrown up into space, and not very much of its core.

The low density of the Moon means that it has less mass, and less gravity. If you ever get a chance to stand on the Moon, you’ll see that its gravity is only 16.5% the gravity of Earth. In other words, if you weight 100 kg on Earth, you would only weigh 16.5 kg on the Moon.

Want to know the density of other objects in the Solar System? Here’s the density of Jupiter, the density of the Sun, and the density of Saturn (the least dense planet in the Solar System).

Want more information about the Moon? Here’s NASA’s Lunar and Planetary Science page. And here’s NASA’s Solar System Exploration Guide.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

The composition of the Moon is a bit of a mystery. Although we know a lot about what the surface of the Moon is made of, scientists can only guess at what the internal composition of the Moon is. Here’s what we think the Moon is made of.

Like the Earth, the Moon has layers. The innermost layer is the lunar core. It only accounts for about 20% of the diameter of the Moon. Scientists think that the lunar core is made of metallic iron, with small amounts of sulfur and nickel. Astronomers know that the core of the Moon is probably at least partly molten.

Outside the core is the largest region of the Moon, called the mantle. The lunar mantle extends up to a distance of only 50 km below the surface of the Moon. Scientists believe that the mantle of the Moon is largely composed of the minerals olivine, orthopyroxene and clinopyroxene. It’s also believed to be more iron-rich than the Earth’s mantle.

The outermost layer of the Moon is called the crust, which extends down to a depth of 50 km. This is the layer of the Moon that scientists have gathered the most information about. The crust of the Moon is composed mostly of oxygen, silicon, magnesium, iron, calcium, and aluminum. There are also trace elements like titanium, uranium, thorium, potassium and hydrogen.

Want to compare the Moon to other objects in the Solar System? Here’s what the Earth is made of, and here’s what Mars is made of.

Want more information about the Moon? Here’s NASA’s Lunar and Planetary Science page. And here’s NASA’s Solar System Exploration Guide.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

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Want to help your kids learn more about the Moon with some interesting activities? Here are some Moon activities that we can suggest:

• Learn the phases of the Moon – For this activity, you need a bright light to represent the Sun, and a ball that you can use as the Moon. Have your child sit on a chair away from the light. The child is the Earth. Then orbit the child in a counter-clockwise direction. The child should see the different amounts of illumination on the ball representing the Moon.
• Organize the phases of the Moon – Draw out all the Moon phases on pieces of paper and mix them all up. Let your children arrange them into the proper order, starting with the new moon going to the full moon, and then back again. You can refer to a calendar of Moon phases if you need to know if they’re right.
• Make craters – Drop marbles or ball bearings into a material that shows how craters can form. To make your lunar surface, put a layer of a white material, like flour in a pan to a depth of a few cm. Then cover it with a thin layer of something dark, like cocoa powder. When you drop the marbles into the material, it will create very familiar looking craters.
• Feel your weight on the Moon – Calculate your child’s weight on the Moon by multiplying their current weight by 0.165. For example, if they weigh 30 kg, they would only weigh 5 kg on the Moon. Have them stand on a bathroom scale and then support their weight until the scale shows their moon weight. Now let them walk around the room with you supporting the bulk of their weight. That’s what it would feel like to walk on the Moon.

Want more activities? NASA has a huge list of cool space activities on their website.

We also have instructions on how you can build a model of the Solar System.

Want more information about the Moon? Here’s NASA’s Lunar and Planetary Science page. And here’s NASA’s Solar System Exploration Guide.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?

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The Moon, on average, is about 150 million kilometers away from the Sun. That’s actually an interesting coincidence, since the Earth orbits about 150 million kilometers away from the Sun. What? Well, the Moon orbits the Earth, so it’s following the Earth around in its orbit around the Sun.

Now, we can actually get a little more precise here. The Earth actually takes an elliptical path around the Sun. It ranges in distance from 147 million km to 152 million km. So the Moon can actually range in this distance as well.

But wait, we can get even more precise. The Moon takes an elliptical orbit around the Earth. Sometimes it gets as close as 363,000 km, and other times it gets as far as 406,000 km.

So the closest point that the Moon can get to the Sun is when the Earth is at its closest point in orbit, and the Moon is most distant from the Earth. The closest point that the Moon can actually get to the Sun is 146,692,378 km.

The furthest that the Moon can get from the Sun is the opposite situation. The Earth is at its most distant from the Sun, and the Moon is furthest from the Earth. At that point, the Moon would be 152,503,397 km.

And that’s how far the Moon is from the Sun.

Here’s more information about how far the Moon is from Earth, and how far the Earth is from the Sun.

Want more information about the Moon? Here’s NASA’s Lunar and Planetary Science page. And here’s NASA’s Solar System Exploration Guide.

You can listen to a very interesting podcast about the formation of the Moon from Astronomy Cast, Episode 17: Where Did the Moon Come From?