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ORION (Pronounced oh-RYE-un), the Hunter

Chart showing Orion

Orion, the Hunter, has been admired throughout historical times as one of the most brilliant, recognisable and symmetrical constellations. Orion straddles the celestial equator, making it visible equally well from both hemispheres. Ptolemy assigned thirty-eight stars to it, including the nebulous one remarked about in very early times.

Many of the bright Orion stars are very hot, young and of early spectral type. This particularly applies to the multiple star θ Orionis or Trapezium where the very hot stars are radiating ultra-violet light causing the Orion nebula M 42 to fluorescence, making the glow that we see. These stars are burning hydrogen so rapidly that their lives cannot be long. In the Orion nebula stars are still being formed from the huge gas and dust cloud.

Two huge star associations that are too large to be telescopic objects have been identified. One is in the region of Orion's belt, and is surrounded by a large, very faint nebula known as Barnard's Loop. The other is associated with faint nebulosity around l Ori.

To find Orion, look towards the north late evening. Find the "Pot".

Chart showing Orion as seen high in the sky to the north mid evening in January.

Constellation Orion

Constellation Eridanus Constellation Lepus Constellation Canis Major Constellation Monoceros Constellation Gemini Constellation Taurus

Details of some of the objects shown in the chart.

The Great Nebula in Orion M42 (NGC 1976) is one of the most attractive objects in the sky. It can be seen with the unaided eye, looks beautiful in binoculars, and is stunning through a telescope. Visually, it appears different from pictures, since photographs cannot cope with the large brightness range between the Trapezium stars and the fainter nebula. In three dimensions the nebula is like an apple with a bite taken out, exposing the pips (the Trapezium stars). The Trapezium stars have blown out the "bite" from the apple (the gas and dust cloud).

α Ori, Betelgeuse (pronounced BET'l-jooz) (Armpit of the Central One) is an irregular variable star of low density that pulsates in and out. Its diameter is about 800 times the diameter of the Sun or 7.5 times the diameter of Earth's orbit. It lies 310 light years away.

β Ori, Rigel (pronounced RYE-j'l) (Giant's leg) at magnitude 0.1 is the brightest star in Orion. It is a blue-white supergiant 910 light years away.

γ Ori, Bellatrix (pronounced beh-LAY-trix) (the conqueror) magnitude 1.70 is a blue giant star 360 light years away.

κ Ori, Saiph (the sword) is a magnitude 2.20 blue supergiant 1,300 light years away.

The "Belt" stars are three bright stars of similar brightness. They are:

δ Ori, Mintaka (pronounced min-TARK-ah) (the belt), at magnitude 2.50, is a complex multiple star.

ε Ori, Alnilam (pronounced al-NIGH-lam) (string of pearls), magnitude 1.80 is a blue supergiant 1200 light years away.

ζ Ori, Alnitak (pronounced al-NIGH-tak) (the girdle), magnitude 2.00 is a blue white star 1100 light years away with a close 4.2 magnitude companion.

Visibility

The three bright stars forming the line of Orion's belt, with the four bright stars at the corners of a tall near rectangle, make Orion possibly the most recognisable of the constellations. From New Zealand it is visible to the northwest in the late evening by the end of November. By mid January it is to the north and at its highest.

With the lengthening dark evenings, the constellation remains visible in the early evening into May. By the end of May, as the evening sky darkens Orion is visible low to the west, lying on its side with Rigel to the left, Betelgeuse to the right and the belt nearly vertical.

In the pre-dawn morning sky, Orion is first visible about the beginning of July a little to the north of east. Rigel is then uppermost and the belt almost horizontal.