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A HUNTING TRIP

By Tom Campbell

Winter is a great time of year for stargazers. The nights are longer and the sky is usually more transparent. Standing out in the winter sky is the constellation of Orion, the Hunter. Perhaps second only to the Big Dipper in Ursa Major, Orion's Belt is one of the most recognizable patterns of stars in the northern sky.

Orion - His Story

Orion, the hunter, stands by the river Eridanus and is accompanied by his faithful dogs, Canis Major and Canis Minor. Together they hunt various celestial animals, including Lepus the rabbit and Taurus the bull.

According to Greek mythology, Orion was the son of Neptune and the Amazon Queen Euryale. He was of gigantic size and strength, and very handsome. Like his father, he was able to walk on water. One day he walked to the island of Chios where he got drunk and attacked Merope, one of the Seven Sisters (Pleiades). Merope's father Oenopion blinded Orion and drove him away.

Eventually, Helios the Sun restored his sight. Like his mother, Orion was a great hunter. He went to Crete and went on a great hunt with the goddess Diana and her mother Leto. During this hunt, Orion threatened to kill every beast on Earth.

When Gaia, the goddess of the Earth, heard of his threat, she angrily sent a tiny scorpion to kill Orion. Scorpius, the scorpion, succeeded, and Orion fell to the ground dead.

The goddesses felt sorry for him, so they begged Zeus to place him in the sky among the constellations. Zeus agreed and placed him in the sky forever chasing after the Pleiades. He also put all of the animals Orion hunted up there near him. Scorpius, however, was placed on the opposite side of the sky so Orion would never be hurt by it again.

Orion's Belt

The constellation of Orion is host to a wide variety of celestial delights. The three bright stars (Alnitak, Alnilam and Mintaka) in a straight line that form Orion's Belt are easily visible in winter evenings. Each of these stars offers something special.

Starting with the rightmost star in the belt, δ(Delta) Orionis, or Mintaka, is a nice double star that can be split in even a small telescope. The white primary is much brighter than the blue companion. Together, they make a gorgeous pair.

Another interesting fact about Mintaka is that it is almost exactly on the celestial equator. Any star north of it will be visible from anywhere in the northern hemisphere and any star south of it will be visible from anywhere in the southern hemisphere.

The leftmost star of the belt is known as ζ(Zeta) Orionis, or Alnitak. It is a triple star system. The brightest two stars are very close together and will take good seeing conditions and a lot of magnification to split them.

Image from "Stellarium" Freeware Planetarium Software

Using my 8" dob at 305X, I was able to make out that both appeared white, with one star being just a little fainter than the other. The third component is much dimmer, but is far enough away from the others to easily seen at low magnification. It appeared blue-white to me.

More Surprises - IC 432 (Flame Nebula)

In dark skies, Alnitak may reveal a couple more surprises. IC 432, commonly known as the Flame Nebula, lies a mere 15' east of Alnitak, and is best seen by nudging the scope enough to put the bright star just out of view. My 8-inch dob was able to detect it at low magnification from a dark site.

Horsehead Nebula

Just south of Alnitak is the more elusive Horsehead Nebula (Barnard 33), a tiny dark spire inside the IC 434 nebula complex. Very dark skies and a narrow-band (such as UHC or H-beta) filter are recommended to see this shy celestial horse.

Middle Belt Star

The middle belt star is ε (Epsilon) Orionis, or Alnilam. It, along with the other two belt stars, are part of a wide open star cluster known as Collinder 70. Centering your binoculars or a low-power widefield telescope on Alnilam will reveal several of the more than 100 members of this cluster. Collinder 70 is over 3 degrees wide and is the brightest open cluster in the sky.

Orion's Sword

Below the belt stars are Orion's sword. There are several worthy sights within the sword that are visible with even a modest telescope, but even your naked eye can see its greatest treasure: the Great Orion Nebula (Messier 42). This cloud of nebulosity is a stellar nursery, where stars are still forming. The Hubble Space Telescope has imaged over 700 stars in various stages of formation within M42.

Using a telescope, you can see billows of nebulosity. In my 8" dob under moderately dark skies, the nebulosity appears dark green, but smaller apertures show it only as varying shades of gray. To me, it almost looks like a bird with two large outstretched wings curving away from the center.

The Trapezium

Within M42 is a small grouping of stars known as the Trapezium, or θ (Theta) Orionis. The brightest four stars form a trapezoidal shape that give the cluster its name and can be seen at pretty modest apertures. Larger apertures and a bit of magnification will be able to reveal a fifth, and even a sixth member of this cluster.

De Mairan's Nebula

Right above M42 and looking like a topknot is Messier 43, also known as De Mairan's Nebula. It is part of the same nebula complex as M42 but is separated by a narrow band of dark nebulosity. In a telescope, it appears bright and oval-shaped.

Mermaid's Purse

About 20 arcminutes north of M42 lies a patch of nebulosity containing NGC 1973, NGC 1975 and NGC 1977. Collectively, they're commonly called the Mermaid's Purse. And inside the purse are some patches of darker nebulosity that form a stick figure known as the Running Man. The purse is pretty bright and with my 8-inch even in light polluted skies I was able to detect some dark patches, but it takes a pretty dark sky at that aperture to reveal the entire running man.

Collinder 73

Moving north another 15 arcminutes brings us to a bright open cluster, NGC 1981. It is also known as Collinder 73 and has a popular name of the Coal Car Cluster. Even a small telescope reveals several members.

Collinder 72

The other end of Orion's sword also contains delights. About half a degree below M42 is NGC 1980, or Collinder 72. Called the Lost Jewel of Orion, this open cluster sparkles with more than a dozen stars of varying magnitudes, including the brightest member, Hatysa.

Rubber Stamp Nebula

Going another degree south to the end of the sword reveals a final treasure. NGC 1999, or the Rubber Stamp Nebula is a little gem that is much smaller and fainter than M42 but still visible in small to medium telescopes. Seasoned amateur astronomer and author Stephen James O’Meara refers to NGC 1999 as the 13th Pearl, not only because of its round and polished appearance, but because it is one of 13 Dwarf Nebulae in the area surrounding Orion’s Belt and Sword, which also includes IC 423, IC 426, IC 430, IC 431, IC 432, IC 435, M78, NGC 1973, NGC 1975, NGC 2064, NGC 2067, and NGC 2071. It is also known as the Black Eye Nebula because embedded in the middle of it is a small, dark patch. Originally, the small patch was believed to be a thick patch of nebulosity that was blocking the light behind it, but recent (2009) observations determined that it is black because it is an actual hole in the nebulosity where no background stars are shining through. It will take some magnification and a dark sky to get enough contrast to see this patch.

σ (Sigma) Orionis

About one degree southeast of Alnitak is a fainter, but still naked-eye star known as σ (Sigma) Orionis. This is actually a quintuple star system. The AB components have a separation of a mere 0.25 arcseconds and appear as a single star except under nights of extremely good seeing.

Rigel

β(Beta) Orionis, commonly called Rigel, is the bright star that makes up the right foot of the hunter. It is the brightest star in Orion and the seventh brightest star in the night sky. It is also a double star, having a companion that would be easily seen if it weren't so close and if Rigel weren't so much brighter. Both stars appear white.

Orion Molecular Cloud Complex

Another Messier object, M78, can be found 2.5 degrees north of Alnitak. It belongs to group of nebulae called the Orion Molecular Cloud Complex. Another part of this nebula is NGC 2071, which can be seen in the same field. Through my 8" dob, the two nebulae were visible as a wide pair of stars with some background nebulosity. The two sides of the nebula closest to the stars were squared off. Some have likened its shape to the cartoon character Casper the Friendly Ghost.

Orion Cluster

Moving up to the chin area of Orion, we see a small naked-eye grouping of stars known as the Orion Cluster, or Collinder 69. The brightest member is λ (Lambda) Orionis, or Meissa, which means The Shining One. Meissa itself is a double star, whose companion can be easily seen in a small telescope. Binoculars will reveal about 10 stars in this cluster whereas a telescope will reveal more than 50 members. Three of the brighter members form a miniature version of Orion's Belt.

Betelgeuse

To the left of the Orion Cluster is the unmistakable Betelgeuse, or α(Alpha) Orionis. This red supergiant is the ninth-brightest star in the night sky. It is so large that if you put it where the sun is in our solar system, it would stretch out nearly all the way to Jupiter.

It is nearing the end of its short lifespan and is expected to explode as a supernova anytime within the next 100,000 years. It's at a safe distance away, however - about 724 light years - so the only real effect on Earth will be its visibility in the daytime sky for a few weeks.

"37" Cluster

Moving up the outstretched arm of Orion above Betelgeuse, we come to NGC 2169, or the "37" Cluster. Its location forms a triangle with ν (Nu) Orionis and ξ(Xi) Orionis. This cluster contains a number of bright stars in a distinctive pattern that remind some people of the numbers 37 written in the sky. Others see XY or LE, and still others see a shopping cart. What do you see?