Orion

Abbreviation:: Ori
English name:: Orion
Coordinates: see Stellar data

Particulars:

Nebulae M 42 (Large Orion Nebula), M 43 (De Mairan Nebula), M 78
Binaries beta Ori, delta Ori, zeta Ori, eta Ori, theta1 Ori, theta2 Ori, iota Ori, lambda Ori, Struve 750, Struve 747
Multiple star cluster sigma Ori, Struve 761
Star cluster NGC 1981
Irregularly variable star alpha Ori
Meteor Showers: Orionids, Chi Orionids

General:

A constellation, which is the head of a constellation family, located in the equatorial region of the sky and belongs certainly to the most famous constellations. It extends from RA=4h 40m to RA=6h 20m and DECL=+23 degrees to DECL=+8 degrees.
In some ways the central part of this constellation reminds on a oblique sand-glass. In wintertime Orion is a magnificent constellation which can easily be found by the the three stars forming a line building the belt of the Hunter. The belt stars point towards Sirius, the brightest star in the constellation of the Larger Dog, Canis Major, situated SE of Orion.
From his belt there hangs a well defined deggar, which is known for one of the most famous nebulas in the sky: The Large Orion Nebula (M42).
Orion lies close enough to the Milky Way to be interesting enough to be swept even with low-power telescopes or binoculars.
Additionally to the data given above there is a skychart to locate the stars and objects.

Stars and objects

The shoulder star alpha Ori, Betelgeuse, is a variable red giant; its brightness varies from 0.4 mag to 1.3 mag with no set period. It belong to the 20 brightest stars in the sky. During it pulsations the diameter of the star varies from 300 to 400 times the diameter of the sun.
The leg of the hunter, beta Ori, Rigel (arab.: the foot), is a blue-white giant of 0.08 mag. This makes it the sixth brightest star in the sky and the brightest in the constellation Orion. With medium sized telescopes it is possible to distinguish the companion of Rigel, a 7th mag star (smaller telescopes may fail to reveal the companion because of the glare of Rigel).
This constellation offers a great number of binaries and multiple stars:
For binoculars and smaller telescopes the following stars are of interest:

delta Ori, Mintaka (arab.: upper end of the girdle), a blue-white star of 2.2 mag with a 7th mag companion.
iota Ori, a 3rd mag and a 7th mag star forming an unequal double; in the same field the wider double
Struve 747 can be found - a pair of a 5th mag and a 6th mag star.
lamba Ori, a tight pair of 4th and 6th mag stars.
sigma Ori is a terrific multiple star; in binoculars this blue-white star of 4 mag and a 7th mag companion can be resolved; using a small telescope two closer companions of 7th mag and 10th mag are revealed. These stars are grouped in a way that they look like a planet with moons.
If the resolution is not too high in the same telescopic field as sigma Ori the triple star Struve 761 can be seen. It consists of a triangle of 8th mag and 9th mag stars. Together with sigma Ori this triple star gives a delightfully rich grouping.
NGC 1981, a little cluster of 10 stars including the binary Struve 750, a pair of a 6th mag and a 8th mag star.
The multiple star theta1 Ori, the northern star of the deggar of the Hunter is also called the Trapezium; it is located in the heart of the Orion nebula. This group of stars has been formed from the gas of the nebula, which now glows in their light. Small telecopes (about 2-inch and higher) show four stars, ranging from 5th mag to 8th mag, which form a rectangular figure. Scopes with an aperture of about 100 mm show two more stars of 11th mag in this group.
Next to it lies theta2 Ori, a duo of a 5th and a 6th mag star.

For resolving the tight double of zeta Ori (Alnitak) in its consisting parts, a bright star of 2.02 mag and a 4th mag companion, scopes with an apertur of at least 75mm and a high resolution are required. Further more there is a wider companion of 10th mag.
Eta Ori is a difficult pair. Scopes with an aperture of 100 mm and higher are necessary to split it into its 4th mag and 5th mag stars.
The constellation Orion became most famous for its nebula. The Messier database has detailed information about The Large Orion Nebula M 42 and M 43, the DeMairan nebula, which is a part of the Orion Nebula.
Around October 21 each year the famous Orionid meteor shower reaches its peak. Coming from the the border to the constellation gemini as much as 20 meteors per hour can be seen. More information about this meteor shower and the Chi Orionids, which are active around the beginning of december can be found in the meteor shower calendar by Gary Kronk.

Mythological Background:

According to greek mythology Orion died being stung by a scorpion. He is set such in the sky that he sets in the west while his slayer, the Scorpius raises in the east.
Followed by his two dogs he is now fighting the bull Taurus.
According to Secrets of the Night Sky (Bob Berman, William Morrow &Co, 1995) the ancient Sumerians saw in this star pattern a sheep. The name Betelgeuse literally means "the armpit"; in case of the Sumerians it meant "the armpit of the sheep."

C. Kronberg --- 97/03/29 --- smil