When is the best time to observe 31 Orionis?

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

Where is 31 Orionis located in the sky?

31 Orionis lies in the constellation Orion at right ascension 05h 30m and declination -01° 06′.

What telescope do I need to split 31 Orionis?

Splitting 31 Orionis requires an aperture of roughly 60 mm or larger — the components are separated by about 12.7″ at magnitudes near 4.7. The companion is about 5.0 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

31 Orionis — Double Star in Orion

Magnitude 4.7^m DoubleStar Orion (Ori) Visible

Star Map + List + Plan

Observe

1Physical Properties

Magnitude 4.71

Range 4.68 - 4.72

Period 141 days

Variable Type Semi-Regular Variable

Spectral Type K5III giant

Star Color Red (B-V 1.57)

Distance 544 ly

2Position & Identifiers

RA 05h 29m 44.0s

Dec -01° 05' 32.0"

Constellation Orion (Ori)

HR 1834

HIP 25737

HD 36167

SAO 132176

Flamsteed 31 Ori

Variable ID CI Ori

Double Cat 4097

SIMBAD

3How easy to split?

Primary 4.7 mag Companion 9.7 mag Separation 12.7″

Telescope	Bortle 3	Bortle 4	Bortle 5
80 mm refractor 80mm refr.	Medium+	Medium+	Medium
150 mm Newton 150mm Newt.	Easy	Easy	Medium+
Celestron C8 (203 mm SCT) C8 203mm	Easy	Easy	Easy

Easy Medium Hard Very hard Impossible

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

4Visibility

Set a location in User Settings to see visibility data.

Best season Nov – Jan (peak: Dec)

5Light Curve

6Multiple Star System

Separation 12.7″

Companion Mag 9.7

Position Angle 87°

Star Colors A: Red

Discoverer STF 725

Notes

CPM. Companion 9.70V, +0.71(B-V), +0.15(U-B), F7V.

Separation over time

Measured 1829 → 2015 (186 y)

Separation drift 12.7" → 12.7" (+0.00")

Rate +0.0000" / y

PA drift 88° → 87° (-1°, -0.005°/y)

Essentially fixed on human timescales — the same view your grandchildren will see.

Measured from the WDS observational archive. No orbital solution has been derived — most likely the period is too long to fit an orbit to the available measurement arc.