Category: Astronomy

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The constellation of Serpens is unique – being the only one to be divided into two parts. Serpens Caput represents the western half. Serpens was one of the 48 constellations listed by the 1st century astronomer Ptolemy and it remains one of the 88 modern constellations. The entire constellation spans 637 square degrees of sky and contains 9 main stars within its asterism and 57 Bayer Flamsteed designated stars within its confines. Serpens Caput is bordered by the constellations of Hercules, Corona Borealis, Virgo, Libra, Bootes and separated from its counterpart by Ophiuchus. Serpens Caput can be seen by all observers located at latitudes between +80° and ?80° and is best seen at culmination during the month of July.

In mythology, Serpens represents a huge snake held by the constellation Ophiuchus. It can either be referred to as simply “Serpens” or by its western half (Caput – the “Snake’s Head”) or its eastern half (Cauda – the “Snake’s Tail”). Ophiuchus was believed to have been the son of Apollo and a healer. According to legend, the snake is also meant to represent healing as it sheds its skin in rebirth.

Let’s begin our binocular tour of Serpen Caput with its brightest star – Alpha Serpentis – the “a” symbol on our map. Alpha Serpentis goes by the proper name Unukalhai, meaning loosely the “heart of the serpent”. Alpha Serpentis is approximately 73.2 light years from Earth and it is a great binary star for a small telescope. The primary, Alpha Serpentis A is an orange K-type giant star about 15 times larger than our Sun and its 11th magnitude B star is about 58 arcseconds from the primary. But don’t stop there! If skies are steady, power up and keep looking for the 13th magnitude C star located 2.3 arcminutes from A.

Now, aim your telescope towards Theta – the “8” symbol on our chart. Theta Serpentis is located 132 light years from our solar system and goes by the name of Alya, which means “fat tail”. Guess what? It’s also a great multiple star system! Both Theta-1 Serpentis and Theta-2 Serpentis are white A-type main sequence dwarf stars, very close in magnitude and separated by 22 arcseconds, but Theta Serpentis C is a yellow G-type star that is widely separated from this par by about 7 arc minutes.

For binoculars and all telescopes, let’s take a look a Messier 5 (RA 15 : 18.6 Dec +02 : 05). At nearly unaided eye visible, you’ll like this one! This fifth brightest globular cluster in the sky is considered one of the most ancient at 13 billion years old. Located further away from the dusty galactic center, resolution explodes as we move up in aperture. Easily seen as a round ball of unresolved stars in binoculars, small scopes begin to pick up individual stellar points at higher magnifications. Careful attention shows that M5 is not perfectly round. Its brightest 11th and 12th magnitude stars actually are randomly distributed but seem to array themselves in great arcs.

For a big telescope challenge, try NGC 6118 (RA 16 : 21.8 Dec -02 : 17). It is a very low surface brightness, 13th magnitude spiral galaxy, and although its fairly large, it’s pretty hard to see in small telescopes. This quality has given rise to the nickname the “Blinking Galaxy”, since it only seems to appear during averted vision – only to disappear if the angle isn’t right. About 80 million light-years away, NGC 6118 is a grand-design spiral seen at an angle, with a very small central bar and tightly wound spiral arms. Thank to imagining by the VLA, we know more about this galaxy than ever. In 2004 a supernova event was caught near the galaxy’s center – believed to be the collision of two binary stars!

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

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The small constellation of Scutum was originally created by Johannes Hevelius in 1683 and was later adopted as a permanent constellation by the IAU. It resides just north of the ecliptic plane or about 10 degrees south of the celestial equator and spans 109 square degrees of sky, ranking 84th in constellation size. There are 2 main stars in Scutum’s asterism and it contains 7 Bayer Flamsteed designated stars within its confines. It is bordered by the Aquila constellation, Sagittarius and Serpens Cauda. Scutum is visible to all observers located at latitudes between +80° and ?90° and is best seen at culmination during the month of August.

There is one annual meteor shower associated with the constellation of Scutum – the June Scutiids. Beginning on or about June 2 and ending about July 29th, we pass into the meteoroid stream which brings on the activity. The peak date for this meteor shower is on or about June 27 and the maximum fall rate is 2-4 meteors per hour.

The constellation of Scutum wasn’t named for a mythological figure – but rather for an object to honor a classical one. In, 1683, Johannes Hevelius, who originally named it Scutum Sobiescianum (the shield of Sobieski), did to commemorate the victory of the Polish forces led by King John III Sobieski in the Battle of Vienna, and thus the name refers to Sobieski’s Janina Coat of Arms. Rather fitting, since this particular king helped Hevelius rebuild his observatory after it was destroyed by fire! It’s Latin name means “shield” and the name was later shortened to Scutum when it was adopted as a permanent constellation by the International Astronomical Union.

Let’s begin our binocular tour of Scutum with its brightest star – Alpha – the “a” symbol on our map. Alpha Scuti is an orange class K giant star located about 175 light years from Earth. While it is not uncommon for this type of star to be over 130 times brighter than our Sun and more than 20 times larger – what’s unusual is the way it has evolved. According to its mass, Alpha should be about 2 billion years old and beginning to fuse helium to carbon… However, it has been discovered that Alpha is slightly variable – meaning it could be shedding its outer layer and on the way to becoming a white dwarf star!

Now, have a look at Delta – the “8” symbol on our chart. Here’s a peculiar star if there ever was one… A star so strange that it’s the prototype of its class. Delta is a giant star – but it is also a variable star. Located 187 light years from our solar system, this metal-rich oddity shines 33 times brighter than our Sun, but it’s only about twice as big. Deep inside, it has stopped fusing hydrogen and it is on its way to becoming a red giant star. But, it’s pulsing like a heartbeat… Changing its magnitude by about 20% every 5 to 65 hours. Added to this are periods of 2.79 hours, 2.28 hours, 2.89 hours, and 20.11 hours. All of this adds up to a very complex rhythm which makes Delta unique! Now, take a look in a telescope, too… Because Delta isn’t alone – it is also a binary star. Look for a 12th magnitude companion 15.2 seconds of arc away from the primary and a 9th component 52.2 seconds away.

For binoculars and small telescopes, head off to Messier 11 (RA 18 : 51.1 Dec -06 : 16)! This incredible galactic star cluster was discovered in 1681 by German astronomer Gottfried Kirch at the Berlin Observatory, M11 was later cataloged by Charles Messier in 1764 and first dubbed the “Wild Duck” by Admiral Smyth. To our modern telescopes and binoculars, there is little doubt as to how this rich galactic cluster earned its name – for it has a distinctive wedge-shaped pattern that closely resembles a flight of ducks. This fantastic open cluster of several thousand stars (about 500 of them are magnitude 14 or brighter) is approximately 250 million years old. M11 is easily located by identifying Altair, the brightest star in Aquila. By counting two stars down the “body” of Aquila and stopping on Lambda, you will find your starhop guide. Near Lambda you will see three stars, the centermost is Eta Scuti. Now just aim! Even small binoculars will have no problem finding M11, but a telescope is required to start resolving individual stars. The larger the telescope’s aperture the more stars will be revealed in this most concentrated of all open clusters!

Keep binoculars and rich field telescopes handy as you shift over to Alpha Scutum and check east-northeast for neighboring 7.8 magnitude open cluster NGC 6664 (RA 18 : 36.7 Dec -08 : 13) . Compare the view to Scutum’s other Messier open cluster – similar sized M26 (RA 18 : 45.2 Dec -09 : 24). As one of the faintest Messier clusters, it’s surprising his scope was able to reveal it at all! To locate Messier 26 shift a little less than 3 degrees south-southeast of Alpha. Those with larger scopes should look for a strange void in the middle of the cluster.

Now, let’s go with a large telescope and have a look at globular cluster NGC 6712 (RA 18 : 53.1 Dec -08 : 42). At magnitude 8, it can be captured with smaller aperture, but requires some muscle to resolve! NGC 6712 was probably discovered by Le Gentil on July 9, 1749 when investigating the Milky Way star cloud in Aquila, but we know it was independently discovered by William Herschel on June 16, 1784. As for its nature? That took John Herschel, who was the first to described it as a “globular star cluster” during his observations in the 1830s!

Last, but not least, let’s do something that you don’t even need a telescope for – R Scuti. This terrific red variable star ranges from 4th to 8th magnitude in 142 days. Chances are, R is probably a red supergiant star, surrounded by a shell of material thousands of times bigger than the interior star itself. One day, it will drop its envelope – turning into a planetary nebula and the star into a white dwarf… But until then? We can simply enjoy this beautiful mystery star!

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

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The small constellation of Sculptor is located south of the ecliptic plane. It was originally charted by Abbe Nicolas Louis de Lacaille who named it “Apparatus Sculptoris” – the Sculptor’s Studio. It was later adopted by the International Astronomical Union as one of the 88 modern constellations and its name shortened to Sculptor. It covers 475 square degrees of sky and ranks 36th in constellation size. Sculptor has 4 main stars in its asterism and contains 18 Bayer Flamsteed designated stars within its boundaries. It is bordered by the constellations of Cetus, Aquarius, Piscis Austrinus, Grus, Phoenix and Fornax. Sculptor is visible to all observers located at latitudes between +50° and ?90° and is best seen at culmination during the month of November.

Since Sculptor is considered a “new” constellation, there is no mythology associated with it – only the story of how its name came to be. French astronomer Nicolas Louis de Lacaille charted the southern hemisphere skies from the Cape of Good Hope during the time period of 1751-1752 and his love of all objects in art and science were portrayed in the names he assigned to his newly created constellations. Depicted on his chart as a fanciful tripod with a carved bust and the artist’s tools, ” l’Atelier du Sculpteur” was later shortened to the simpler term – Sculptor – and adopted by the International Astronomical Union as a permanent constellation.

Let’s begin our binocular tour of Sculptor with its brightest star – Alpha – the “a” symbol on our map. Located approximately 680 light years from Earth, Alpha Sculptoris is a blue-white B-type giant classified as an SX Arietis type variable star and its magnitude varies by 0.01. While changes in brightness and spectral composition that small would never be detectable to the human eye, at one time it was believed to be caused by orbiting black hole – but were later identified to chemical variations in its atmosphere. While Alpha doesn’t appear to be much, take a closer look… It still shines over 1700 times brighter than our own Sun – yet is only 7 times larger! It is one of the weirdest stars you will ever see – a helium weak star that rotates ever-so-slowly. Thanks to this creeping motion, Alpha can generate a huge stellar magnetic field which allows it to concentrate its chemicals in certain areas – and even flip its magnetic poles!

For other binocular attractions, take a look at Beta Sculptoris – the “B” symbol. It’s a a blue-white B-type subgiant star positioned approximately 178 light years from our solar system. Or Gamma – the “Y” symbol – it’s an an orange K-type giant that is 179 light years away… or even Delta – the “8” symbol. Delta is is a triple star system that’s 139 light years distant and the primary component, Delta Sculptoris A, is a white A-type main sequence dwarf star! Take out the telescope and look for a faint, 11th magnitude companion, Delta Sculptoris B, 4 arcseconds, or more than 175 AU, away from it. Orbiting this pair at the much greater separation of 74 arcseconds, is the third player in this drama, the yellow G-type Delta Sculptoris C, which has an apparent stellar magnitude of 9.4.

For telescope observers, one of the greatest challenges you will ever encounter is the Sculptor Dwarf Galaxy (RA 01 : 00.0 Dec -33 : 42). Discovered by Harlow Shapley on photographic plates in 1937, this extreme low surface brightness elliptical galaxy is a member of our own local galaxy group and is about 290,000 light-years away. Use at least a 150mm telescope and an absolute minimum of magnification to spot just a compression in the starfield at this location!

Now, let’s take a look at the Sculptor Group – a a loose group of galaxies near the south galactic pole and one of the closest groups of galaxies to the Milky Way Local Group. At the head of this class is the Sculptor Galaxy – NGC 253 – is an intermediate spiral galaxy (RA 0 : 47.6 Dec -25 : 17). Discovered by Caroline Herschel, this brilliant magnitude 7 beauty is a starburst galaxy, undergoing periods of intense star formation, and can easily be seen with a small telescope or binoculars. However, companion galaxies NGC 247, PGC 2881, PGC 2933, Sculptor-dE1, and UGCA 15 will need much more aperture! This association forms a gravitationally bound core near the center of the group and most other galaxies associated with the Sculptor Group are only weakly gravitationally bound to this core.

While there, drop south and take a look at NGC 288 (RA 00:52:47.5 Dec -26:35:24). This 8th magnitude globular cluster was discovered by Sir William Herschel and can often be spotted in the same binocular field as NGC 253. While this small globular doesn’t appear to be worthy of much attention, think again… In the late 1980’s it was discovered that it is about 3 billion years older than other globular clusters!

Need to take a look at the home of a supernova? The stop by NGC 150 (RA 0 : 34.3 Dec -27 : 48). Home to an event in 1990, this spiral galaxy is also a great radio emitter, too. Even though it will require a larger telescope to catch anything at magnitude 11, it will still give a nice oblong presentation with a bright core region.

For another binocular and small telescope galaxy, take a look at NGC 55 (RA 0 : 14.9 Dec -39 : 11). This huge, magnitude 8 irregular galaxy gives a great, near edge-on presentation and is believed to be very similar to the Large Magellanic Cloud (LMC). Spanning about 50,000 light-years, large telescopes will be able to resolve out brighter regions of emission nebulae – large star forming regions producing new stars.

For an unusual mid-size telescope challenge, take a look at NGC 7793 (RA 23 : 57.8 Dec -32 : 35). At magnitude 9 and about 9 arc minutes in size, you’ll find 10 million light year distant Bennett 130 to be a beautiful spiral with a sharp nucleus and round, hazy spiral galaxy structure. It was discovered by James Dunlop and it is also part of the Sculptor Group. In 2005, the Spitzer Space Telescope was able to pierce through its clouds and take a closer look at star formation driving the evolution of the galaxy.

Don’t forget while you’re in Sculptor to take on large telescope challenges like NGC 7713 (RA 23 : 36.5 Dec -37 : 56) – a 12th magnitude spiral galaxy, NGC 7755 (RA 23 : 47.9 Dec -30 : 31), also 12th magnitude, but a much smaller elliptical galaxy. How about small and faint NGC 24 (RA 0 : 09.9 Dec -24 : 58) or far easier NGC 134 (RA 0 : 30.4 Dec -33 : 15). There’s galaxies galore just waiting to be carved out of Sculptor and enjoyed!

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

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The zodiacal constellation of Scorpius resides on the ecliptic plane and was one of the original 48 constellations charted by Ptolemy to be later adopted as a modern constellation by the IAU. It covers 497 square degrees of sky and ranks 33rd in size. Scorpius has 15 main stars in its asterism and 47 Bayer Flamsteed designated stars within its confines. It is bordered by the constellations of Sagittarius, Ophiuchus, Libra, Lupus, Norma, Ara and Corona Australis. Scorpius is visible to all observers located at latitudes between +40° and ?90° and is best seen at culmination during the month of July.

There are two annual meteor showers associated with the constellation of Scorpius. The first is the Alpha Scorpiids – which begin on or about April 16 and end around May 9. The peak date of most activity is on or about May 3 and the radiant is near the brilliant red star, Antares. The second meteor shower, the June Scorpiids peaks on or about June 5 of each year. The radiant for this particular meteor shower is closer to the Ophiuchus border and the activity rate on the peak date is high – with about 20 meteors (average) per hour and many reported fireballs.

Because Scorpius was easy visible to ancient civilizations and its patterns do resemble the Scorpion which it represents, there is a great deal of mythology associated with this constellation. To the Greeks it represented the creature sent by Hera to eliminate Orion the Hunter – forever kept apart in the sky to continue their heavenly feud. Perhaps it was Apollo who sent the Scorpion and Orion flees it? Scorpius was also said to appear to Phaethon, who wrecked the sun-chariot when the horses balked at the mighty monster’s appearance. The Oriental culture recognized this pattern of stars as part of the Dragon, while the Polynesians saw it as a fishhook. No matter what legend you choose to place on this pattern of stars, its curving asterism is very distinctive and easy to recognize!

Let’s begin our binocular tour of Scorpius with its brightest star – Alpha – the “a” symbol on our chart. Antares is part of of the Upper Scorpius Association of Stars and is no doubt also a star poised on the edge of extinction. At a safe distance of 500 light-years, you’ll find this pulsating red variable equally fascinating to the eye as well as to the telescope. Unlike other stars, Alpha Scorpii also has a companion which can be revealed to small telescopes under steady conditions. Discovered on April 13, 1819 during a lunar occultation, this 6.5 magnitude green companion isn’t the easiest to split from such a bright primary – but it’s certainly fun to try to spot its 5.4 magnitude green companion. Like winter’s Sirius, the Antares pair needs especially still – but not necessarily dark – skies. It also requires a well-chosen magnification – one high enough to separate the two close stars (2.9 arc seconds), but low enough to concentrate the fainter star’s (magnitude 5.4) light. Did you know that Antares’ true rival is brighter Betelgeuse? Photometric measurements show that more massive Betelgeuse is slightly redder than Antares. Fortunately, the “Rival” does reside along the ecliptic plane allowing us many opportunities to see it accompany other solar system objects and be occulted by the Moon!

Keep your binoculars handy because all you have to know is Antares and go west…

Just slightly more than a degree away you’ll find a major globular cluster perfectly suited for every size telescope and binoculars – M4 (RA 16 23 35 Dec 26 31 31). This 5th magnitude Class IX cluster can even be spotted unaided from a dark location! In 1746 Philippe Loys de Cheseaux happened upon this 7200 light-year distant beauty – one of the nearest to us. It was also included in Lacaille’s catalog as object I.9 and noted by Messier in 1764. Much to Charles’ credit, he was the first to resolve it!

As one of the loosest globular clusters, M4 would be tremendous if we were not looking at it through a heavy cloud of interstellar dust. To binoculars, it is easy to pick out a very round, diffuse patch – yet it will begin resolution with even a small telescope. Large telescopes will also easily see a central “bar” of stellar concentration across M4’s core region, which was first noted by William Herschel. As an object of scientific study, the first millisecond pulsar was discovered within M4 in 1987 – one which spins 10 times faster than the Crab Nebula pulsar. Photographed by the Hubble Space Telescope in 1995, M4 was found to contain white dwarf stars – the oldest in our galaxy – with a planet orbiting one of them! A little more than twice the size of Jupiter, this planet is believed to be as old as the cluster itself. At 13 billion years, it would be three times the age of the Sol system!

Keep your binoculars or a small telescope handy as well go off to explore a single small globular cluster – Messier 80. Located about 4 degrees northwest of Antares (half a fist), this little globular cluster is a powerpunch. Located in a region heavily obscured by dark dust, the M80 will shine like an unresolvable star to small binoculars and reveal itself to be one of the most heavily concentrated globulars to the telescope. Discovered within days of each other by Messier and Mechain respectively in 1781, this intense cluster is around 36,000 light years distant.

In 1860, the M80 became the first globular cluster to contain a nova. As stunned scientists watched, a centrally located star brightened to magnitude 7 over a period of days and became known as T Scorpii. The event then dimmed more rapidly than expected, making observers wonder exactly what they had seen. Since most globular clusters contain stars all of relatively the same age, the hypothesis was put forward that perhaps they had witnessed an actual collision of stellar members. Given the cluster contains more than a million stars, the probability remains that some 2700 collisions of this type may have occurred during the M80’s lifetime.

Now head for Lambda Scorpii and hop three fingerwidths northeast to NGC 6406 (RA 17 40 18 Dec -32 12 00)… We’re hunting the “Butterfly!” Easily seen in binoculars and tremendous in the telescope, this brilliant 4th magnitude open cluster was discovered by Hodierna before 1654 and independently found by de Cheseaux as his Object 1 before being cataloged by Messier as M6. Containing about 80 stars, the light you see tonight left its home in space around the year 473 AD. Messier 6 is believed to be around 95 million years old and contains a single yellow supergiant – the variable BM Scorpii. While most of M6’s stars are hot, blue, and belong to the main sequence, the unique shape of this cluster gives it not only visual appeal, but wonderful color contrast as well.

Less than 3 arc minutes east of 3.3 magnitude G Scorpii (the tail star of the Scorpion) is 7.4 magnitude globular cluster NGC 6441. No challenge here. This 38,000 light-year distant compact cluster is around 13 thousand light-years from the galactic core. It was first noted by James Dunlop from southeastern Australia in 1826.

Around two and a half degrees northeast of G Scorpii (and NGC 6441) is another interesting deep sky twosome – bright open cluster M7 and faint globular NGC 6453. M7 was first recorded as a glowing region of faint stars by Ptolemy circa 130 CE. Located 800 light-years away, the cluster includes more than half a dozen 6th magnitude stars easily resolved with the least amount of optical aid. Through telescopes, as many as 80 various stars can be seen and it rocks in binoculars!

Now head northeast and the faint haze of 31,000 light-year distant globular cluster NGC 6453 will reveal itself to mid- and large-sized scopes. Like NGC 6441, this globular cluster was discovered from the southern hemisphere, in this case by John Herschel on June 8, 1837 while observing from the Cape of Good Hope, South Africa.

It’s time to aim your telescope at NGC 6302, a very curious planetary nebula located around three fingerwidths west of Lambda Scorpii: it is better known as the “Bug” nebula (RA 17 13 44 Dec -37 06 16). With a rough visual magnitude of 9.5, the Bug belongs to the telescope – but it’s history as a very extreme planetary nebula belongs to us all. At its center is a 10th magnitude star, one of the hottest known. Appearing in the telescope as a small bowtie, or figure 8 shape, huge amounts of dust lie within it – very special dust. Early studies showed it to be composed of hydrocarbons, carbonates and iron. At one time, carbonates were believed associated with liquid water, and NGC 6302 is one of only two regions known to contain carbonates – perhaps in a crystalline form.

Ejected at a high speed in a bi-polar outflow, further research on the dust has shown the presence of calcite and dolomite, making scientists reconsider the kind of places where carbonates might form. The processes that formed the Bug may have begun 10,000 years ago – meaning it may now have stopped losing material. Hanging out about 4000 light-years from our own solar system, we’ll never see NGC 6302 as well as the Hubble Telescope presents its beauty, but that won’t stop you from enjoying one of the most fascinating of planetary nebulae!

Now begin your starhop at the colorful southern Zeta pair and head north less than one degree for NGC 6231 (RA 16 : 54.0 Dec -41 : 48). Wonderfully bright in binoculars and well resolved to the telescope, this tight open cluster was first discovered by Hodierna before 1654. De Cheseaux cataloged it as object 9, Lacaille as II.13, Dunlop as 499, Melotte as 153, and Collinder as 315. No matter what catalog number you chose to put in your notes, you’ll find the 3.2 million year young cluster shining as the “Northern Jewelbox!” For high power fans, look for the brightest star in this group – it’s van den Bos 1833, a splendid binary.

About another degree north is loose open cluster Collinder 316, with its stars scattered widely across the sky. Caught on its eastern edge is another cluster known as Trumpler 24, a site where new variables might be found. This entire region is encased in a faint emission nebula called IC 4628 – making this low power journey through southern Scorpius a red hot summer treat!

When you are done, hop west (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!

There are many, many more splendid object to be discovered in the constellation of Scorpius, so be sure to get a detailed star chart and enjoy!

Sources:
Wikipedia
Chandra Observatory
Chart Courtesy of Your Sky.

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The zodiacal constellation of Sagittarius resides on the ecliptic plane and was one of the original 48 constellations charted by Ptolemy to be later adopted as a modern constellation by the IAU. It spans 867 square degrees of sky and ranks 15th in constellation size. It has 7 primary stars in its main asterism and 68 Bayer Flamsteed designation stars within its confines. Sagittarius is bordered by the constellations of Aquila, Scutum, Serpens Cauda, Ophiuchus, Scorpius. Corona Australis, Telescopium, Indus, Microscopium and Capricornus. It is visible to all observers located at latitudes between +55° and ?90° and is best seen at culmination during the month of August.

The easily recogniged “tea pot” shape of Sagittarius was well known in mythology as being represented by the half-man, half-horse – the Centaur. According to some legends, he was the offspring of of Philyra and Saturn. Named Chiron, he turned himself into a horse to hide from his jealous wife and was eventually immortalized in the stars. He is often depicted as an archer as well, with his arrow pointed directly at the red heart of the Scorpion – Antares. Sagittarius may represent the son of Pan, who invented archery and was sent to entertain the Muses who threw a laurel wreath at his feet. No matter what identity you choose, one thing is for certain – there’s no mistaking the presence of the nearby Sagittarius arm of the Milky Way!

(Since the constellation of Sagittarius is simply slopping over with deep sky objects, creating a small, workable chart here would be very confusing. For this reason, I have only chosen a few of my favorite objects to highlight and I hope you enjoy them, too!)

Let’s begin our binocular tour of Sagittarius with its alpha star – the “a” symbol on our map. Located far south in the constellation, Alpha Sagittarii is far from being the brightest of its stars and goes by the traditional name of Rukbat – the “knee of the Archer”. It’s nothing special. Just a typical blue, class AB dwarf star located about 170 light years from Earth, but it often gets ignored because of its position. Have a look at Beta while you’re there, too. It’s the “B” symbol on our map. That’s right! It’s a visual double star and its name is Arkab – the “hamstring”. Now, power up in a telescope. Arkab Prior is the westernmost and it truly is a binary star accompanied by a 7th magnitude dwarf star and seperated by about 28 arcseconds. It’s located about 378 light years from Earth. Now, hop east for Arkab Posterior. It is a spectral type F2 giant star, but much closer at 137 light years in distance.

Now turn your attention towards Epsilon Sagittarii – the backwards “3” symbol on our chart. Kaus Australis is actually the brightest star in the bottom righthand corner of the teapot and the brightest of all the stars in Sagittarius and the 36th brightest in the night sky. Hanging out in space some 134 light years from our solar system, this A-class giant star is much hotter than most of its main sequence peers and spinning over 70 times faster on its axis than our Sun. This rapid movement has caused a shell to form around the star, dimming its brightness… But not nearly as dim as its 14th magnitude companion! That’s right… Epsilon is a binary star. The disparate companion is well seperated at 32 arc seconds, but will require a larger telescope to pick away from its bright companion!

Ready for more? Then have a look at Gamma – the “Y” symbol on our map. Alnasl, the “arrowhead” is two star systems that share the same name. If you have sharp eyes, you can even split this visual double star without aid! However, take a look in the telescope… Gamma-1 Sagittarii is a Cepheid 1500 light year distant variable star in disguise. It drops by almost a full stellar magnitude in just a little under 8 days! Got a big telescope? Then take a closer look, because Gamma-1 also shows evidence of being a close binary star, as well has having two more distant 13th magnitude companions, W Sagittarii B, and C separated by 33 and 48 arcseconds respectively. How about Gamma-2? It’s just a regular type-K giant star – but it’s only 96 light years from Earth!

Located just slightly more than a fingerwidth above Gamma Sagittarii and 5500 light-years away, NGC 6520 (RA 18 03 24 Dec -27 53 00) is a galactic star cluster which formed millions of years ago. Its blue stars are far younger than our own Sun, and may very well have formed from what you don’t see nearby – a dark, molecular cloud. Filled with dust, Barnard 86 literally blocks the starlight coming from our galaxy’s own halo area in the direction of the core. To get a good idea of just how much light is blocked by B 86, take a look at the star SAO 180161 on the edge. Behind this obscuration lies the densest part of our Milky Way! This one is so dark that it’s often referred to as the “Ink Spot.” While both NGC 6520 and B 86 are about the same distance away, they don’t reside in the hub of our galaxy, but in the Sagittarius Spiral Arm. Seen in binoculars as a small area of compression, and delightfully resolved in a telescope, you’ll find this cluster is on the Herschel “400” list and many others as well.

Are you ready for a whirlwind tour of the Messier Catalog objects with binoculars or a small telescope? Then let’s start at the top with the “Nike Swoosh” of M17.
Easily viewed in binoculars of any size and outstanding in every telescope, the 5000 light-year distant Omega Nebula was discovered by Philippe Loys de Chéseaux in 1745-46 and later (1764) cataloged by Messier as object 17 (RA 18 20 26 Dec -16 10 36). This beautiful emission nebula is the product of hot gases excited by the radiation of newly born stars. As part of a vast region of interstellar matter, many of its embedded stars don’t show up in photographs, but reveal themselves beautifully to the eye at the telescope. As you look at its unique shape, you realize many of these areas are obscured by dark dust, and this same dust is often illuminated by the stars themselves. Often known as “The Swan,” M17 will appear as a huge, glowing check mark or ghostly “2” in the sky – but power up if you use a larger telescope and look for a long, bright streak across its northern edge with extensions to both the east and north. While the illuminating stars are truly hidden, you will see many glittering points in the structure itself and at least 35 of them are true members of this region, which spans up to 40 light-years and could form up to 800 solar masses. It is awesome…

Keeping moving south and you will see a very small collection of stars known as M18, and a bit more south will bring up a huge cloud of stars called M24. This patch of Milky Way “stuff” will show a wonderful open cluster – NGC 6603 – to average telescopes and some great Barnard darks to larger ones. M24 is often referred to as the “Small Sagittarius Star Cloud”. This vast region is easily seen unaided from a dark sky site and is a stellar profusion in binoculars. Telescopes will find an enclosed galactic cluster – NGC 6603 – on its northern border. For those of you who prefer a challenge, look for Barnard Dark Nebula, B92, just above the central portion.

Now we’re going to shift to the southeast just a touch and pick up the M25 open cluster. M25 is a scattered galactic cluster that contains a cephid variable – U Sagittarii. This one is a quick change artist, going from magnitude 6.3 to 7.1 in less than seven days. Keep an eye on it over the next few weeks by comparing it to the other cluster members. Variable stars are fun! Head due west about a fist’s width to capture the next open cluster – M23. From there, we are dropping south again and M21 will be your reward. Head back for your scope and remember your area, because the M20 “Triffid Nebula” is just a shade to the southwest. Small scopes will pick up on the little glowing ball, but anything from about 4″ up can see those dark dust lanes that make this nebula so special. The “Trifid” nebula appears initially as two widely spaced stars – one of which is a low power double – each caught in its own faint lobe of nebulosity. Keen eyed observers will find that the double star – HN 40 – is actually a superb triple star system of striking colors! The 7.6 magnitude primary appears blue. Southwest is a reddish 10.7 magnitude secondary while a third companion of magnitude 8.7 is northwest of the primary.

Described as “trifid” by William Herschel in 1784, this tri-lobed pattern of faint luminosity broken by a dark nebula – Barnard 85 – is associated with the southern triple. This region is more brightly illuminated due to the presence of the star cluster and is suffused with a brighter, redder reflection nebula of hydrogen gas. The northern part of the Trifid (surrounding the solitary star) is fainter and bluer. It shines by excitation and is composed primarily of doubly ionized oxygen gas. The entire area lies roughly 5000 light-years away. What makes M20 the “Trifid” nebula, are the series of dark, dissecting dust lanes meeting at the nebula’s east and west edges, while the southernmost dust lane ends in the brightest portion of the nebula. With much larger scopes, M20 shows differences in concentration in each of the lobes along with other embedded stars. It requires a dark night, but the Trifid is worth the hunt. On excellent nights of seeing, larger scopes will show the Trifid much as it appears in black and white photographs!

You can go back to the binoculars again, because the M8 “Lagoon Nebula” is south again and very easy to see. Easily located about three finger-widths above the tip of the teapot’s spout (Al Nasl), M8 is one of Sagittarius’ premier objects. This combination of emission/reflection and dark nebula only gets better as you add an open cluster. Spanning a half a degree of sky, this study is loaded with features. One of the most prominent is a curving dark channel dividing the area nearly in half. On its leading (western) side you will note two bright stars. The southernmost of this pair (9 Sagittarii) is thought to be the illuminating source of the nebula. On the trailing (eastern) side, is brightly scattered cluster NGC 6530 containing 18 erratically changing variables known as “flare stars.” For large scopes, and those with filters, look for small patches of dark nebulae called “globules.” These are thought to be “protostar” regions – areas where new stars undergo rapid formation. Return again to 9 Sagittarii and look carefully at a concentrated portion of the nebula west-southwest. This is known as the “Hourglass” and is a source of strong radio emission.

This particular star hop is very fun. If you have children who would like to see some of these riches, point out the primary stars and show them how it looks like a dot-to-dot “tea kettle.” From the kettle’s “spout” pours the “steam” of the Milky Way. If you start there, all you will need to do is follow the “steam” trail up the sky and you can see the majority of these with ease.

At the top of the “tea kettle” is Lambda. This is our marker for two easy binocular objects. The small M28 globular cluster is quite easily found just a breath to the north/northwest. The larger, brighter and quite wonderful globular cluster M22 is also very easily found to Lambda’s northeast. Ranking third amidst the 151 known globular clusters in total light, M22 is probably the nearest of these incredible systems to our Earth, with an approximate distance of 9,600 light-years. It is also one of the nearest globulars to the galactic plane. Since it resides less than a degree from the ecliptic, it often shares the same eyepiece field with a planet. At magnitude 6, the class VII M22 will begin to show individual stars to even modest instruments and will burst into stunning resolution for larger aperture. About a degree west-northwest, mid-sized telescopes and larger binoculars will capture the smaller 8th magnitude NGC 6642 (RA 18 31 54 Dec -23 28 34). At class V, this particular globular will show more concentration toward the core region than M22. Enjoy them both!

Now we’re roaming into “binocular possible” but better with the telescope objects. The southeastern corner of the “tea kettle” is Zeta, and we’re going to hop across the bottom to the west. Starting at Zeta, slide southwest to capture globular cluster M54. Keep heading another three degrees southwest and you will see the fuzzy ball of M70. Just around two degrees more to the west is another globular that looks like M70’s twin. The small globular M55 is out there in “No Man’s Land” about a fist’s width away east/south east of Zeta .

Ready for a big telescope challenge? Then try your hand at one the sky’s most curious galaxies – NGC 6822. This study is a telescopic challenge even for skilled observers. Set your sights roughly 2 degrees northeast of easy double 54 Sagittarii, and have a look at this distant dwarf galaxy bound to our own Milky Way by invisible gravitational attraction…

Named after its discoverer (E. E. Barnard – 1884), “Barnard’s Galaxy” is a not-so-nearby member of our local galaxy group. Discovered with a 6″ refractor, this 1.7 million light-year distant galaxy is not easily found, but can be seen with very dark sky conditions and at the lowest possible power. Due to large apparent size, and overall faintness (magnitude 9), low power is essential in larger telescopes to give a better sense of the galaxy’s frontier. Observers using large scopes will see faint regions of glowing gas (HII regions) and unresolved concentrations of bright stars. To distinguish them, try a nebula filter to enhance the HII and downplay the star fields. Barnard’s Galaxy appears like a very faint open cluster overlaid with a sheen of nebulosity, but the practiced eye using the above technique will clearly see that the “shine” behind the stars is extragalactic in nature.

Now look less than a degree north-northwest to turn up pale blue-green NGC 6818 – the “Little Gem” planetary. Easily found in any size scope, this bright and condensed nebula reveals its annular nature in larger scopes but hints at it in scopes as small as 6″. Use a super wide field long-focus eyepiece to frame them both!

Be sure to get a good star chart and enjoy the constellation of Sagittarius to its fullest potential – there’s lots more out there!

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