When is the best time to observe Tau Orionis?

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

Where is Tau Orionis located in the sky?

Tau Orionis lies in the constellation Orion at right ascension 05h 18m and declination -06° 51′.

What telescope do I need to split Tau Orionis?

Splitting Tau Orionis requires an aperture of roughly 60 mm or larger — the components are separated by about 35.4″ at magnitudes near 3.6. The companion is about 7.3 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Tau Orionis — Double Star in Orion

Magnitude 3.6^m DoubleStar Orion (Ori) Visible

Star Map + List + Plan

Observe

1Physical Properties

Magnitude 3.60

Spectral Type B6IV subgiant

Star Color Blue-white (B-V -0.11)

Distance 494 ly

2Position & Identifiers

RA 05h 17m 36.4s

Dec -06° 50' 40.0"

Constellation Orion (Ori)

HR 1735

HIP 24674

HD 34503

SAO 131952

Bayer Tau

Flamsteed 20 Ori

Double Cat 3877

SIMBAD

3How easy to split?

Primary 3.6 mag Companion 10.9 mag Separation 35.4″

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

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)

5Multiple Star System Quadruple B: optical

Components 4 (quadruple)

Component IDs AD

Separation 35.4″

Companion Mag 10.9

Position Angle 61°

Star Colors A: Blue-white

Discoverer HJ 2259

Separation over time

Measured 1868 → 2011 (143 y)

Separation drift 36.0" → 35.4" (-0.60")

Rate -0.0042" / y

PA drift 61° → 61° (+0°, +0.000°/y)

Slow change over generations — observable in lifetime comparisons.

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.