오리온

Orion is the brightest and probably best known constellation in the sky. In the Northern Hemisphere, Orion can best be seen in the winter towards the southern horizon. 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

The constellation Orion was listed by the Greek astronomer Ptolemy in the second century AD. However, it was recorded by the Babylonians as early as 686 BCE in the astronomical tablets MUL.APIN, as the SIPA.ZI.AN.NA, "the Loyal Shepherd of Heaven." It has even been considered that the Belt of Orion may be represented in the cave paintings of Lascaux, which were made in approximately 15,000 BCE. Orion is so ancient that the constellation is part of the Sumerian narrative of Gilgamesh. The relative position of Orion in the sky sets the figure next to Taurus, and Orion is often depicted as facing off against the bull. Dating as far back as the 18th century BCE, the Mesopotamian Epic of Gilgamesh pits URU AN-NA, meaning "the Light of Heaven," against GUD AN-NA, "the Bull of Heaven." The Light of Heaven represents the constellation we know today as Orion, and the Bull of Heaven represents the constellation now called Taurus.

Orion is a great figure in Greek mythology and dates back to the seventh or eighth century BCE in both the Iliad and the Odyssey. In the Iliad, Orion is noted as a constellation accompanied by his dog Sirius. Homer tells of Odysseus' encounter with Orion in the underworld during the eleventh book of the Odyssey, where the great hunter roamed the underworld with a club of bronze.

In Roman mythology, Orion was a great hero of large stature, reputed to be the son of Poseidon. These legends fit more with Roman variants of the story. As a son of Poseidon, Orion was able to cross any sea. Orion attempted to seduce Merope, the daughter of King Oenopion. But the king did not approve, and commanded Orion to rid the island of wild beasts in exchange for his daughter, thinking that Orion would certainly fail at this impossible task. Orion, however, was a great hunter and completed the task for the king, whereupon Oenopion went back on his word and had Orion blinded. Orion traveled to the edge of the world to find Aurora, the goddess of dawn, who cured him.

A different origin story, meant to emphasize the rewards of hospitality to strangers, was told by the Greeks. Hyrieus of Boeotia took in three strangers and fed them a roasted bull. Unknown to Hyrieus, the guests were Zeus, Poseidon, and Hermes in disguise. As a reward for his great hospitality, the gods granted Hyrieus the gift of a son: the gods urinated on the hide of the roasted bull and buried it in the earth. With the help of the earth-goddess Gaia, a child was born. This child born of the earth was named Orion.

There are two versions of Orion's death in Greek mythology. In the first, while hunting on Crete, Orion boasted that he could kill any animal on Earth. Gaia took offense and cracked the earth open, from which a scorpion emerged to kill Orion. In the second version, Orion attempted to forcibly break Artemis' vows of chastity. Threatened, Artemis summoned the scorpion that killed Orion. Because of his heroism in life in both tales, Zeus was asked to place Orion into the heavens. Zeus put Orion into the sky, but found it fitting to put the scorpion in the sky as well. To this day, it is said that Orion is still running from the beast that killed him with its deadly sting. This is reflected in Orion descending or "running away" as Scorpius is rising. Scorpius has already set in autumn as Orion rises, and as Scorpius rises in the summer Orion has already set in the western horizon. Both are ancient fables elucidating the cost of hubris.

Sailors have marked the rising of Orion as a sign signaling the start of winter and harsh weather in the Northern Hemisphere. In Mayan cultures, the belt of Orion was considered a turtle. The Arabs called this constellation Al Jabbar "the Giant," which sits upon a throne we view as the constellation Lepus.

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 eleventh 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 that of our sun. 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 seventh 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 this star 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 that 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 actually 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 hues 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.



NGC 1977, lying just north of the Orion Nebula complex (M 42). Robert Gendler.
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 under 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 the American astronomer E. E. Barnard, who captured it on long-duration film exposures in 1895.