Epsilon Orionis
From Wikipedia, the free encyclopedia
 Alnilam lights up NGC 1990. Photograph by Glen Youman. |
|
| Observation data Equinox J2000 |
|
|---|---|
| Constellation | Orion |
| Right ascension | 05h 36m 12.8s |
| Declination | −01° 12′ 06.9″ |
| Apparent magnitude (V) | 1.70 |
| Characteristics | |
| Spectral type | B0 Iab |
| U-B color index | −1.03 |
| B-V color index | −0.19 |
| Variable type | Alp Cyg |
| Astrometry | |
| Radial velocity (Rv) | 25.9 km/s |
| Proper motion (μ) | RA: 1.49 mas/yr Dec.: −1.06 mas/yr |
| Parallax (π) | 2.43 ± 0.91 mas |
| Distance | approx. 1300 ly (approx. 400 pc) |
| Absolute magnitude (MV) | −6.4 |
| Details | |
| Mass | 40 M☉ |
| Radius | 26 R☉ |
| Luminosity | 375,000 L☉ |
| Temperature | 25,000 K |
| Metallicity | ? |
| Rotation | ~87 km/s |
| Age | 4 × 106 years |
| Other designations | |
| Database references | |
| SIMBAD | data |
Epsilon Orionis (ε Ori / ε Orionis) is a large blue star in the constellation of Orion. It also has the traditional name Alnilam. Its Flamsteed designation is 46 Orionis.
It is the 30th brightest star in the sky (the 4th brightest in Orion) and as a blue-white supergiant it is one of the most luminious stars known. It is the middle star of Orion's belt.
It is also one of the 57 stars used in celestial navigation. For middle latitudes, it is at its highest point in the sky around midnight on December 15.
Alnilam's relatively simple spectrum has made it useful for studying the interstellar medium. Within the next million years, this star may turn into a red supergiant and explode as a supernova. It is surrounded by a molecular cloud, NGC 1990, which it brightens to make a reflection nebula. Its stellar winds may reach up to 2000 km/s, causing it to lose mass about 20 million times more rapidly than the Sun.
[edit] Other names and history
The name Alnilam derives from the Arabic النظام an-niżām, related to the word نظم nażm "string of pearls". Related spellings are Alnihan and Alnitam: all three variants are evidently mistakes in transliteration or copy errors.
Various other names have been used to refer to Orion's belt, the line of three stars formed by Alnitak, Alnilam, and Mintaka. They include:
- The Weighing Beam (Chinese mythology)
- Jacob's Staff, Peter's Staff, the Three Magi, or the Three Kings (the Bible)
- Freya's Staff (Norse mythology)
- Väinämöinen's Scythe (Kalevala)
- Kalevan Sword (Finnish mythology)
These stars also allegedly influenced the construction of the Pyramids of Giza.
