Orion


Orion


English nameOrion

Major
stars
alpha OrionisBetelgeusemagn. 0,5RA: 05h 55m 10.32sDec: +07 24' 25.4"
beta OrionisRigelmagn. 0,1RA: 05h 14m 32.28sDec: -08 12' 06.0"
gamma OrionisBellatrixmagn. 1,6RA: 05h 25m 07.86sDec: +06 20' 58.7"
delta OrionisMintakamagn. 2,4RA: 05h 32m 00.40sDec: -00 17' 56.8"
epsilon OrionisAlnilammagn. 1,8RA: 05h 36m 12.81sDec: -01 12' 07.0"
zeta OrionisAlnitakmagn. 2,0RA: 05h 40m 45.52sDec: -01 56' 33.5"
eta Orionismagn. 3,4RA: 05h 24m 28.64sDec: -02 23' 49.4"
iota Orionismagn. 2,9RA: 05h 35m 25.98sDec: -05 54' 35.6"
kappa OrionisSaiphmagn. 2,2RA: 05h 47m 45.39sDec: -09 40' 10.8"
pi3 Orionismagn. 3,3RA: 04h 49m 50.34sDec: +06 57' 40.6"

DescriptionSplendid constellation of the equatorial region, emphasized by a big number of bright stars assembled in a not very vast zone. In particular there are Betelgeuse, a red supergiant 300 light-years away, and Rigel, a blue supergiant 900 light-years away, that with its magnitude 0,1 is the seventh star in order of brightness.

A peculiarity of the constellation is a trio of stars set on a line between Betelgeuse and Rigel: they are Mintaka, Alnilam and Alnitak, which individualize Orion's belt. Mintaka and Alnitak are two double stars: to observe the first one you need only small instruments, while the second one is more difficult to be separated since its two components are very near.

Another interesting star is sigma Orionis, situated just under the belt: seen with a small telescope, it shows to be a white-blue star accompanied by well three more weak stars; this gives the impression to see a planet with three satellites.

IC 434Starting from Alnitak and going southwards, you can find the weak nebula IC 434 (on the right), on a side of which there is the Horsehead Nebula, a cloud of dark dusts that extraordinarily resembles a horse. It is impossible to see it to the naked eye: only the long-exposured photos allow to reveal all its charm.

M42But the most famous object of the constellation is rightly the Orion Nebula (on the left), a big cloud of gases and dusts extended for almost a degree and visible to the naked eye too, even though it looks really marvelous only to the telescope. The nebula seems to be cut to two pieces, M42 and M43, by a dark strip calles Fish Mouth, near to which, almost in the heart of the nebula, there is theta1 Orionis, a multiple star which illuminates the surrounding gases: this star is also called Trapezium, since it is constituted by four stars disposed just as a trapezium. The Orion Nebula has a diameter of at least 15 light-years and is about 1300 light-years away from us.


Mythology
and history
Orion was a skilled hunter, son of Poseidon: he was a giant and he was so tall that he could walk on the sea-bed holding his head out of water.

One day Orion arrived at the Chio island, where he asked the king Aenopion for the hand of his daughter Merope: Aenopion consented, on condition that before Orion killed all the beasts that infested his kingdom; but after the giant had completed this exploit, Aenopion didn't fulfil his promise. Orion became very angry, and after having got drunk he raped Merope: therefore Aenopion ordered to blind him and to banish him from Chio. The giant succeeded in reaching Lemno, where he asked the young Caesalius, assistant in the forge of Ephestus, to put on his shoulders and to guide him eastwards: an oracle, in fact, foretold him that he would have recovered the sight if he had directed toward the rising Sun. And so it happened.

About Orion's death there are different stories. A version tells that the giant boasted to be the best hunter ever existed: Artemis, the goddess of hunting, indignant and offensed, make a big scorpio to come out from a fissure and to prick Orion to death. For this reason in the sky, when Scorpius rises, Orion hides himself under the west horizon.
A completely different version says, instead, that Artemis fell in love with Orion and wanted to marry him: but their possible union was not pleasant to Apollo, brother of Artemis. Apollo challenged his sister to a bowshot competition, and pointing out a distant object in the sea, provoked her by saying that she wouldn't be able to strike it: Artemis immediately darted an arrow and didn't miss the target, that however was the head of Orion who walked in the sea. Sorrowful, the goddess set the figure of her lover among the constellations.

In the sky Orion is represented while he is raising the shield (that is the arc of stars denominated pi Orionis) and the cudgel (chi1 and chi2 Orionis) to defend himself from Taurus which is charging him.


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