Trapezium (Theta¹ Orionis)

Trapezium (Theta¹ Orionis) is a double star in the constellation Orion, magnitude 5.1.

The four bright young stars at the heart of the Orion Nebula (M42); the brightest, θ¹ Ori C, provides most of the ultraviolet light that makes the nebula glow. θ¹ Ori C and D (magnitudes 5.1 and 6.7; spectral types O7 V (blue) and B1.5 V (blue-white)) lie 13.8″ apart at PA 60° (measured 2021). A (magnitude 6.7) and B (8.0), both eclipsing binaries, complete the trapezoid, whose widest pair (A–D) spans 21.4″; the fainter E and F, near magnitude 11, need more aperture and steady air.

When and where to see it

It is best placed in the evening sky around January, when it crosses the meridian at about 10 pm local time (around midnight in December). It can be seen from everywhere south of 85°N and never sets south of 85°S.

At its highest it stands 35° up from 50°N, 50° up from 35°N, 85° up from the equator, 60° up from 35°S.

Facts

Type

Double star

Constellation

Orion

Designations

Theta¹ Orionis, θ¹ Ori, Trapezium Cluster, 41 Ori, 41 Orionis, STF 748, HIP 26221

Magnitude

5.1

Position

RA 5h 35.3m, Dec −5° 23′ (J2000)

Open AstroPilot to see when Trapezium (Theta¹ Orionis) is highest tonight from your location, how easy it is with your telescope or binoculars, and an eyepiece view.