Orion - The Hunter

Orion is the brightest and probably best known constellation in the sky. In the Northern Hemisphere, look toward the south in winter to find Orion. The three stars in Orion's belt are a well known pointer to other nearby constellations. The upper part of Orion lies within the Milky Way. Orion's belt runs through the celestial equator, the midpoint in the sky, so his figure is known to observers north and south of the Earth's Equator.

Orion is seen marching across the winter sky, with his dogs, Canis Major and Canis Minor, following behind. Sirius, the brightest star in the sky, lies just southeast of the hunter.

History and Mythology

Orion, the famous Hunter with club in hand, has an ancient mythology. Orion was known as a god, hero, warrior, and hunter by many cultures that named stellar groups. In the 11th book of the Odyssey, Homer speaks of Orion as the lover of the rose-fingered Aurora. He was already named Orion by 425 BC.

In Greek Mythology, Orion was Poseidon's son, and the most handsome man who ever lived. He was a giant, so tall he could wade through any sea with his head above the water. He fell in love with Merope, the daughter of Oenopion. Her father was not in favor of their marriage, so he gave Orion the task of ridding their island of all wild beasts, after which he would give Orion his daughter's hand. Since Orion was fond of hunting, he eagerly took on the task. Soon Orion returned to tell Oenopion that he had cleared the island of all wild beasts. He brought back skins to prove to the king that he had accomplished his task. After talking to the king, Orion realized that he would never give his permission for the marriage. He made plans to carry Merope away by force, but Oenopion learned of his plan and condemned Orion to be blinded and cast out on the seashore. Eventually, Orion regained his sight by looking at the goddess of dawn, Aurora.

Another myth tells us that Orion was a great braggart. He would boast that no game could ever escape him. This angered the goddess Juno, who sent a scorpion to sting the hunter and kill him. Aesculapius, a famous doctor, was called to bring Orion back to life. The god Pluto (or Hades), King of the Dead, heard this news and became worried that doctors awakening the dead would destroy his kingdom. He complained to his brother Zeus, who then threw a thunderbolt at Orion, killing both Orion and the doctor Aesculapius. When these characters were placed in the sky, Sagittarius, the Archer, was posted near the Scorpion as a precaution. Orion and the Scorpion were placed on opposite sides of the sky. Orion shines in winter, Scorpius in the summer; and when one rises, the other sets.

Sailors believed that the rising of Orion's head above eastern oceans marked the start of winter, and brought bad weather in the Northern Hemisphere. The Aborigines of northern Australia saw Orion's belt as three fishermen in a canoe. They broke the fishing laws of their tribe, and they were placed in the heavens as a reminder to anyone who would think of doing the same. The Mayans of Mexico thought that the stars in Orion's belt represented a turtle. In Babylon, Orion was worshipped as the god who created precious stones. Perhaps this is how Betelgeuse was named, because the star is topaz-colored.

Notable Stars

Orion has two first magnitude stars. Betelgeuse is in the left shoulder of the hunter, and Rigel is located in Orion's right foot or knee.

Alpha Orionis, or Betelgeuse, is the 11th brightest star in the sky. The origin of its name is uncertain, but its red color is easily seen. Betelgeuse is the nearest red supergiant star to our solar system, 425 light years away. Betelgeuse pulsates irregularly between magnitudes 0.4 and 1.3 over a period of several years, but this is not noticeable to the casual observer. Its diameter also varies, from 300 to 500 times the Sun's. This instability shows that Betelgeuse is nearing the end of its life, and is due to explode as a supernova at any time - or may have done so already.

Beta Orionis, or Rigel is a bluish, 0.18 magnitude star near Orion's foot; in fact, Rigel means "foot" in Arabic. It is the brightest star in Orion, and the 7th brightest star in the sky. This blue white giant is about 900 light-years away. It has a magnitude 6.7 companion star appearing 9 arcseconds away, but is difficult to observe because of Rigel's brilliant glare.

Gamma Orionis or Bellatrix, "the left shoulder" of Orion, is magnitude 1.6 and about 240 light-years away. It is one of the hotter naked eye stars, and radiates 6400 times the Sun's luminosity.

Three bright stars - Epsilon, Zeta, and Delta Orionis - make up Orion's belt. They are traditionally named Alnilam, Alnitak and Mintaka. Legend claims these stars are the Magi, the Three Wise Men from the East, who traveled west to the Holy Land, following the star which marked the birth of Christ. Second magnitude Mintaka is a multiple star system. A small telescopes reveals companions of magnitude 4.2 and 6.9. The star Alnitak, meaning "belt" in Arabic, is the eastern star in the belt. The third star is Alnilam, meaning "string of pearls" in Arabic, and it is magnitude 1.7.

Kappa Orionis, which has the traditional name Saiph, meaning "sword" in Arabic, and is the sixth-brightest star in the constellation. It is a hot blue supergiant 720 light years away, and marks Orion's lower left foot.

Sigma Orionis is an attractive quintuple star system, whose five stars shine together at magnitude 3.6 just south of Alnitak in Orion's belt. Amateur telescopes show a quartet of stars, the brightest of which is also a close double. This system is about 1150 light years away, and is part of the Orion OB1 Association of young stars which includes many others in the constellation.

Clusters, Nebulae, and Galaxies

There are many famous nebulae in Orion, but the most celebrated is the Great Orion Nebula. It is located in Orion's sword, and it includes both M 42 and M 43. This huge nebula of gas and dust is one of the finest diffuse nebulae in the sky. It is 1400 light years away, and 25 light-years across. Many new stars are constantly being formed in the swirling cloud. The ultraviolet light of these hot stars causes the gas cloud to glow in a fluorescent manner.

The naked eye sees M 42 as a hazy cloud, and a small telescopes show wreaths and swirls of gas. To the eye the nebula appears somewhat greenish; its colorful red and pink colors are only visible in photographs. With a small telescope, one should be able to see the Trapezium, the four tightly grouped stars near the center of the nebula that are responsible for most of the energy that makes it glow. The Trapezium stars are also catalogued as Theta1 Orionis.

The beautiful grouping of reflection nebulae NGC 1973, NGC 1975, and NGC 1977 are often overlooked in favor of the better known Orion Nebula. But this bright nebulous complex is interesting in its own right, and is one of the brightest reflection nebulae in the sky. NGC 1981 is a cluster one degree north of the Great Orion Nebula, at the northern edge of the NGC 1973-75-77 complex. This bright, scattered cluster contains 40 stars covering a 1/2-degree area.

The Flame Nebula, NGC 2024, is a cloud of hot gas near Alnitak that appears reddish. Stretching down from Alnitak is the dark Horsehead Nebula, Barnard 33, which is silhouetted against the bright red background of the emission nebula IC 434. In very dark skies, the Horsehead can be seen in a 6 inch or even smaller telescope. The Horsehead is best seen with long exposure photographs.

Northwest of Alnitak is the reflection nebula M 78. This is the brightest reflection nebula in the sky, visible in binoculars unders good conditions. It is a patch of cold dust illuminated by reflected starlight from nearby stars, and appears comet-like in small telescopes.

All of these nebulae are part of the Orion Molecular Complex, a huge region of gas and dust that envelops the constellation. The Orion Molecular Complex is one of the nearest large star-forming regions to our Solar System. Barnard's Loop is a huge emission nebula surrounding this entire region. Difficult to identify visually, its discovery is generally credited to E. E. Barnard who captured it on long-duration film exposures in 1895.