Orion - 1

Orion is a Equatorial constellation otherwise known as the Hunter. It is one of the 48 Greek constellations originally described by the 2nd century astronomer Claudius Ptolemy (Wikipedia). Orion remains one of the 88 modern constellations defined by the International Astronomical Union (Wikipedia).

Orion (abbrev. = Ori; genitive = Orionis) covers 594 square degrees or 1.44% of the celestial sphere making it the 26th largest constellation. It contains 204 stars brighter than apparent magnitude 6.5, the brightest star being Rigel (Alpha Orionis). Other bright stars include Betelgeuse (Beta Orionis), and Bellatrix (Gamma Orionis). See the Orion Star Chart for a figure illustrating this constellation including the identification of its brighter stars.

Orion is one of the most easily recognized constellations and is best seen from December to March. Being an Equatorial constellation, it is visible from both Northern and Southern Hemispheres.

The most distinguishing naked eye feature of the constellation is the Belt of Orion, an asterism formed by the three bright stars (from left to right) Alnitak (Zeta Orionis), Alnilam (Epsilon Orionis) and Mintaka (Delta Orionis). M42, the Great Nebula in Orion is a complex region of active star formation where some of the hotest and brightest stars are coalescing. Composed of glowing gas and dark dust, this nebula is part of the much larger Orion Molecular Cloud Complex. This immense region also includes M78 and the Horsehead Nebula located south of Zeta Orionis (Alnitak), the easternmost star in the Belt of Orion. Encircling the entire region is the reddish glow of Barnard's Loop.

See Orion 2 for a close-up view of this constellation.

For more information see the entries for Orion at Wikipedia and U. Wisconsin. For a chart of Orion, see Ori (IAU).

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