When is the best time to observe Sigma Orionis?

Sigma Orionis is best observed from November through January, with peak visibility during December when it transits around midnight in the Northern Hemisphere.

Where is Sigma Orionis located in the sky?

Sigma Orionis lies in the constellation Orion at right ascension 05h 39m and declination -02° 36′.

What telescope do I need to split Sigma Orionis?

Splitting Sigma Orionis requires an aperture of roughly 200 mm or larger — the components are separated by about 0.3″ at magnitudes near 3.8. Larger apertures and steady seeing help resolve the pair cleanly.

Sigma Orionis — Double Star in Orion

Magnitude 3.8^m DoubleStar Orion (Ori) Visible

Star Map + List + Plan

Observe

1Physical Properties

Magnitude 3.81

Spectral Type O9.5V

Star Color Blue (B-V -0.24)

Distance 950 ly

2Position & Identifiers

RA 05h 38m 44.8s

Dec -02° 36' 00.0"

Constellation Orion (Ori)

HR 1931

HIP 26549

HD 37468

SAO 132406

Bayer Sigma

Flamsteed 48 Ori

Double Cat 4241

SIMBAD

3How easy to spot?

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Equipment	Bortle 3	Bortle 4	Bortle 5
Naked eye Naked eye	Easy	Medium+	Medium+
50 mm finder 50mm finder	Easy	Easy	Easy
150 mm telescope 150mm scope	Easy	Easy	Easy

Easy Medium Hard Very hard Impossible

Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs

4Visibility

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Best season Nov – Jan (peak: Dec)

5Multiple Star System Quintuple

Components 5 (quintuple)

Component IDs AB

Separation 0.3″

Companion Mag 5.3

Companion Sp B?

Position Angle 239°

Star Colors A: Blue B: Blue

Discoverer BU 1032

Notes

AB 4.1 O9.5V, 5.1 B0.5V, 170y, a = 0.247". Combined mag. and colors. C, 8.79V, A2V at 11" may be physical; D, 6.62V, | -0.20(B-V), B2V, at 13" and E = HR 1932, at 42" CPM with A. A multiple system similar to trapezium. ADS 4241 possibly | the most massive visual binary known, 35 solar masses.