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Theta1 Orionis, the Trapezium Cluster

Open Cluster in the Orion Nebula (M42) in Orion

Right Ascension 05:35:16 (h:m:s)
Declination -05:23:24 (deg:m:s)
Distance 1600 (ly)
Visual brightness 5.0 (mag)
Spectral type O6pe, O7, B0V, B0.5Vp

Discovered as triple star by Galileo Galilei on February 4, 1617.
Independently found as triple star by Christiaan Huygens in 1656.

The first recorded observation of a multiple star character of Theta1 Orionis, the bright stellar object in the Orion Nebula (M42), occurred on February 4, 1617, when it was observed and recorded as triple by Galileo Galilei (Galileo 1617, Fedele 1949, Ondra, Mosher 2005), who did, however, not recognize the Orion Nebula due to unknown reasons.

Reports of a later, independent discovery of Theta1 as triple star of 1654 by Giovanni Batista Hodierna from Palma di Montechiaro, Sicily (Hodierna 1654, Serio et.al. 1985) must be regarded as spurious.

With Galileo's observation generally unrecognized, Theta1 Orionis was independently revealed as triple star in 1656 and described by Christiaan Huygens (Huygens 1659). The fourth component, Theta1 Orionis D, was found by Abbe Jean Picard (1620-1682) in 1673 to complete the "Trapezium." The fourth Trapezium star was independently recovered in 1684 by Christiaan Huygens.

Actually, the Trapezium is a cluster which includes many more stars, which are all very young and have recently formed from matter of the Orion Nebula.

  • More of the Trapezium Cluster
  • The Trapezium Through the Galilean Telescope, by Tom Pope and Jim Mosher


  • Double Star Home

    Hartmut Frommert [contact]