Trapezium Cluster
The Trapezium or Orion Trapezium Cluster, also known by its Bayer designation of Theta1 Orionis (θ1 Orionis), is a tight open cluster of stars in the heart of the Orion Nebula, in the constellation of Orion. It was discovered by Galileo Galilei. On 4 February 1617 he sketched three of the stars (A, C and D), but missed the surrounding nebulosity. A fourth component (B) was identified by several observers in 1673, and several more components were discovered later like E, for a total of eight by 1888. Subsequently, several of the stars were determined to be binaries. Telescopes of amateur astronomers from about 5-inch (130 mm) aperture can resolve six stars under good seeing conditions.
| Trapezium | |
|---|---|
| Observation data (J2000 epoch) | |
| Right ascension | 05h 35.4m |
| Declination | −05° 27′ |
| Distance | 1,344±20 ly (412 pc) |
| Apparent magnitude (V) | 4.0 |
| Apparent dimensions (V) | 47 (seconds of arc) |
| Physical characteristics | |
| Mass | ? M☉ |
| Radius | 10 ly |
| Estimated age | 300,000 years |
| Associations | |
| Constellation | Orion |
The Trapezium is a relatively young cluster that has formed directly out of the parent nebula. The five brightest stars are on the order of 15 to 30 solar masses in size. They are within a diameter of 1.5 light-years of each other and are responsible for much of the illumination of the surrounding nebula. The Trapezium may be a sub-component of the larger Orion Nebula Cluster, a grouping of about 2,000 stars within a diameter of 20 light-years.