The Trapezium or Orion Trapezium Cluster, also known by its Bayer designation of Theta1 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, 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 in optical (left) and infrared light (right) from Hubble. NASA photo
One of the components of the cluster (Theta1 Orionis F, lower left) is a double star.
The Chandra X-ray Observatory view of the Orion Nebula
Trapezium star identification
The Orion Nebula is a diffuse nebula situated in the Milky Way, being south of Orion's Belt in the constellation of Orion,[b] and is known as the middle "star" in the "sword" of Orion. It is one of the brightest nebulae and is visible to the naked eye in the night sky with apparent magnitude 4.0. It is 1,344 ± 20 light-years (412.1 ± 6.1 pc) away and is the closest region of massive star formation to Earth. The M42 nebula is estimated to be 24 light-years across. It has a mass of about 2,000 times that of the Sun. Older texts frequently refer to the Orion Nebula as the Great Nebula in Orion or the Great Orion Nebula.
The entire Orion Nebula in a composite image of visible light and infrared; taken by Hubble Space Telescope in 2006
The constellation of Orion with the Orion Nebula (lower middle)
Messier's drawing of the Orion Nebula in his 1771 memoir, Mémoires de l'Académie Royale
Henry Draper's 1880 photograph of the Orion Nebula, the first ever taken.
