ASTRONOMER'S CORNER

Written by Ted Forte

The constellation of Auriga is prominent on winter evenings. It’s dominated by the bright star Capella, the sixth brightest star in the sky. The name Capella means “she goat” in Latin and the star represents Amalthea, the goat that suckled Zeus in Greek mythology. Auriga represents a charioteer and Capella marks either his left shoulder or the goat that he is carrying. Southwest of Capella is a noted triangle of stars, Epsilon, Zeta, and Eta Aurigae, that are collectively known as The Kids.  Epsilon Aurigae, the apex of that triangle, is perhaps the most enigmatic eclipsing binary star in the heavens – every 27 years or so, it dims for about 2 years. It last dimmed in 2009-2011. Astronomers still aren’t sure exactly what is eclipsing what in this weird system. 

The figure of the Charioteer is formed by a lopsided pentagon of bright stars, with Capella as its northwestern corner, that sits between Gemini and Perseus. Lying as it does along the band of the Milky Way, the constellation is rich in star clusters. Open or galactic clusters are gravitationally bound groups of tens to thousands of stars that were formed together in the same giant molecular cloud, are roughly the same age, and have a similar velocity through space. 

The best known of Auriga’s clusters are the three that made it to the Messier list. The French astronomer, Charles Messier, was an 18th century comet hunter who is famous for his catalog of comet look-alikes: objects that appear comet-like in small telescopes. The three, today known as M36, M37 and M38, were all discovered by the Italian astronomer Giovanni Battista Hodierna before 1654. He saw them each as a “nebulous patch”. The French astronomer, Guillaume Le Gentil, identified M36 and M38 as clusters of stars in 1749. Messier did the same for M37 in 1764. 

M38, aka NGC 1912, lies just a bit north of a line connecting Iota and Theta Aurigae and about midway between the two stars. It’s a lovely cluster of 160 stars. About 120 of those lie in an area half the size of the full moon. About a dozen of its brightest stars form a slanted cross through its center. M38 is over 4,000 light years distant. 

From M38, jump 2.3 degrees southeast to M36 (NGC 1960), a smaller cluster of about 60 stars. While it’s less massive, it’s the brightest of the three Messier clusters in Auriga and is visible to the unaided eye as a fuzzy star. It lies about the same distance away from us as M38. The cluster is estimated to be about 20 to 30 million years old, making it rather young.  The 19th century British astronomer, Thomas Webb, described the cluster as a “beautiful assemblage of stars … very regularly arranged”. The cluster has a loose central condensation of stars with several curving streams radiating out. It vaguely looks cross-like, similar to M38. 

The third Messier cluster is M37 (NGC 2099). It lies outside of Auriga’s pentagon asterism another 3.7 degrees southeast of M36. It’s a bit further away at 4,380 light years. Rich in stars, it probably has about 1800 members; 170 of those stars are brighter than 13th magnitude. At an age of 230 million years, it’s still considered young. This cluster looks more condensed than M36 or M38 and even resembles a loose globular cluster. I think it’s the more impressive of the three. See if you can detect the red tinge of its brightest star. 

A small round cluster, NGC 1907, is just 32’ south-southwest of M38 and will occupy the same field of view in a medium power telescope. It was discovered by William Herschel in 1787.  It’s nearly the same distance from us as M37. Well detached from the background and having a strong central condensation, it contains about 113 stars, generally of similar brightness. See if you can detect a bit of nebulosity associated with the cluster. This is starlight reflecting off of the residual dust and gas that still infuses the cluster. 

Another small cluster that will be obvious in a backyard telescope is NGC 1778. It was discovered by William Herschel on the same night he discovered NGC 1907. He noted it as "a coarsely scattered cluster of large stars”. Containing about 112 stars, it has no central condensation. Look for it 4.5 degrees northeast of Iota Aurigae, the western most star in the pentagon asterism. It’s about 4800 light years away.

There are more than 50 open clusters in Auriga and many of them are visible with binoculars or a small telescope. I hope this small sampling gets you started discovering them. 

Written by Ted Forte

For casual stargazers, December is a great month.  Sunset comes early, and the winter cold is still somewhat at bay. As darkness falls, the winter sky, dominated by billant Orion and containing the brightest stars in the heavens, is rising in the east. High overhead is the Great Square of Pegasus. And sinking in the west, the Summer Triangle, centerpiece of the Autumn sky, is still available. Saturn is perfectly placed, in the south at sunset, and an hour later, Jupiter rises among the stars of Gemini: an easy target by 10 p.m. 

Some fascinating deep sky objects populate the December sky. The easiest to find with your telescope or binoculars will be the Andromeda Galaxy which transits the evening sky in late November. From the northeast corner of the Great Square, follow the line of two bright stars, Delta and Beta Andromedae, that sweep northeast. From Beta, turn northwest and jump to the next bright star, Mu Andromedae. Another jump of about the same distance and your eye can’t miss the fuzzy glow that is the Andromeda Galaxy aka M31. At 2.5 million light years away, M31 is the most distant object we can see with the naked eye. Stretching almost 6 full moons edge to edge, the galaxy is a remarkable object for binoculars. A serious observer with a large telescope might spend a whole night here exploring its numerous knots and star clusters, occasionally wandering to its two satellite galaxies, M32 and M110. 

The constellation Andromeda consists of two curving lines of stars stretching northeast from the Great Square. The northernmost line extends past 51 Andromedae to Phi Persei and just about a degree northwest of Phi is the Little Dumbbell, M76. This bright, bipolar planetary nebula looks like a little peanut. It’s the remnant of an evolved sun-like star that is likely around 3,400 light years away from us. You’ll need a telescope to enjoy it. 

Follow that same line of stars that forms the northern string of Andromeda a little further and your eye will pick out a large fuzzy patch of light. Put your binoculars on it and you’ll be amazed by a splash of stars arranged in two groups. This is the Perseus Double Cluster. Each cluster is a half degree in diameter with the western cluster, NGC 869, having over 200 white and bluish-white members. NGC 884 to the east has 175 stars. They are approximately 700 light years away and just a few hundred light years apart.

Swing your binoculars about 12 degrees southeast to the bright star Mirfak (Alpha Persei). The bright star anchors a beautiful cluster of stars, Melotte 20. The cluster is visible to the naked eye but is spectacular in binoculars. Spanning 3 degrees of sky, the 517 members are around 560 light years away. 

Nine degrees south-southeast of Mirfak is the “Demon Star” Algol. This famous eclipsing binary is usually 2.1 magnitude, but drops to 3.4 magnitude every 2.87 days (50 hours, 49 minutes) as its companion eclipses it. The eclipse lasts 10 hours. Check the web to find its next expected minima and you can watch it dim. 

From Algol, the open cluster M34 is 5 degrees northwest. This cluster of about 400 stars is approximately 1400 light years away and can be detected with the naked eye in a dark sky. 

Halfway between M34 and the bright double star Almaak (Gamma Andromedae) lies a challenging edge-on galaxy that is 30 million light years from us. NGC 891 can be a difficult catch. See if you can detect the faint glow of this slim beauty in your telescope. I’d recommend a scope of at least 10-inch aperture and moderate power of 120x.  

If NGC 891 eludes you, don’t despair, just swing your telescope 3.5 degrees west to enjoy a lovely double star. Almaak is a brilliant orange primary of 2.3 magnitude that seems to touch a whitish blue secondary of 5.1 magnitude. The pair are about 390 light years away. 

For our last stop on this short tour, look directly south of Almaak to the three stars that define the constellation Triangulum. They form an isosceles triangle with its apex, the star Metallah, pointing southwest. About 4 degrees north-northwest of Metallah, you’ll spy the large diffuse glow of the Triangulum Galaxy, M33. This open-faced spiral is the third largest member of the local group of galaxies to which the Milky Way belongs. Look for a faint oval glow surrounded by three graceful arms that will be made apparent by a number of knotty clumps of nebulosity. As with any faint object, the longer you look, the more you’ll see. 

Enjoy this small sample of the many splendors of the December sky!

Written by Ted Forte

Don’t let the nickname fool you. The area of the sky defined by the “Summer Triangle” takes center stage in Autumn. The stars Vega, Deneb, and Altair, the brightest stars in the constellations of Lyra the Harp, Cygnus the Swan and Aquila the Eagle form a recognizable triangle that transits (is due south in the sky) on fall evenings. Within and around this triangle are some of the sky’s most fascinating targets. 

About a third of the way along a line connecting Altair and Vega sits a fun binocular asterism. Known as the “Coat Hanger”, its proper designation is Collinder 399. The brightest 10 stars in this open cluster form the unmistakable image of a wire coat hanger. 

Forming a smaller triangle, with and about equidistant from Vega and Deneb, is the star that forms the head of Cygnus the Swan. It’s named Albireo and designated Beta Cygni. The beta star of a constellation is usually its second brightest star, but in this case, Albireo is the fifth brightest star in Cygnus. Albireo is one of the loveliest double stars in the heavens. An amber 3.1 magnitude primary is paired with a blue 5.1 secondary 35” away. The pair is about 420 light years distant from Earth. 

About 1.7o northeast of Vega is a multiple star system known as the “Double Double” and designated Epsilon Lyrae. Appearing as a single star to the naked eye, your finder scope or binoculars will show it as two stars, approximately 5th magnitude and separated by 3.5’. A telescope in good seeing conditions will reveal that each component of the pair is itself a close double. The north pair is magnitude 6.0 and 4.7 and the south pair are almost equal at about 5th magnitude. Both binaries are just 2.4” apart. The whole system is about 162 light years away.

Binoculars or a wide-field low power telescope will show the “North American Nebula” as a faintly glowing mass directly east of Deneb. So named because its brightest section mimics the Atlantic coast line of North America, it’s officially named NGC 7000. This vast cloud of ionized hydrogen gas is probably about 2,500 light years away.  A UHC (ultra high contrast) filter will greatly enhance the visibility of the nebula and may even make the adjacent “Pelican Nebula” visible as well. 

A filter is a must to enjoy the supernova remnant known as the Veil Nebula. This amazing nebulous complex is the remains of a star 20 times more massive than the sun that exploded about 15,000 years ago. Sections of the Veil have earned their own designations. The two brightest arcs of nebulosity are known generally as the Eastern Veil, NGC 6992, and the Western Veil, NGC 6960. The entire complex is three degrees across and covers an area 36 times the size of the full moon. It probably lies about 2,400 light years away. The Veil is located below the eastern wing of Cygnus. The Western Veil is adjacent to the 4.2 magnitude star 52 Cygni which lies just over 3 degrees south of Epsilon Cygni which marks the tip of the eastern wing. The Eastern Veil is found by moving straight east from the northern tip of the Western Veil about 3 degrees.

The Summer Triangle is home to two of the most famous planetary nebulae in the sky. Planetary nebulae are a late evolutionary stage of sun-like stars. These stellar corpses consist of a glowing circumstellar cloud of ionized gas surrounding an extremely hot central star. The central star is the exposed core of the original star and the glowing cloud that surrounds it is the expelled outer layers of that star. 

Messier 27, also known as the “Dumbbell Nebula” was the very first planetary nebula discovered and, at 1,360 light years, is one of the closest to Earth. You’ll find it 3.20 north of Gamma Sagittae which represents the tip of the arrow. Named for its distinctive dumbbell or apple core shape, it’s large and bright and a popular target for amateur astronomers. 

The “Ring Nebula” or Messier 57, is a star party favorite. It’s small, but very bright and well defined and looks like a ghostly celestial donut or a smoke ring. It’s nestled midway between Beta and Gamma Lyrae, the two stars that form the base of the harp asterism, making it quite easy to find. Based on the number of times I’ve turned a telescope to this little jewel, I’d have to say this is my favorite object in the entire sky! M 57 is about 2,300 light years away. 

These objects are just a sampling of the deep sky splendors that can be found in the area defined by the Summer Triangle.