When is the best time to observe Beta Monocerotis?

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

Where is Beta Monocerotis located in the sky?

Beta Monocerotis lies in the constellation Monoceros at right ascension 06h 29m and declination -07° 02′.

What telescope do I need to split Beta Monocerotis?

Splitting Beta Monocerotis requires an aperture of roughly 80 mm or larger — the components are separated by about 7.3″ at magnitudes near 4.6. Larger apertures and steady seeing help resolve the pair cleanly.

Beta Monocerotis — Double Star in Monoceros

HIP 30867; Beta Monocerotis; 11 Monocerotis

Observable Double Star Showpiece (76/100)

Sep: 7.3", Companion: mag 5.0

Magnitude 3.7–3.9^m DoubleStar Monoceros (Mon) Visible

Star Map + List + Plan

Observe

1Physical Properties

Magnitude 4.60

Range 3.74 - 3.85

Variable Type BE

Spectral Type B3Ve

Star Color Blue (B-V -0.10)

Distance 155 ly

2Position & Identifiers

RA 06h 28m 49.0s

Dec -07° 01' 58.0"

Constellation Monoceros (Mon)

HR 2356

HIP 30867

HD 45726

SAO 133317

Bayer Beta

Flamsteed 11 Mon

Double Cat 5107

SIMBAD Wikipedia

3How easy to split?

Primary 4.6 mag Companion 5.0 mag Separation 7.3″

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Telescope	Bortle 3	Bortle 4	Bortle 5
80 mm refractor 80mm refr.	Easy	Easy	Easy
150 mm Newton 150mm Newt.	Easy	Easy	Easy
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

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Best season Nov – Jan (peak: Dec)

5Multiple Star System Quadruple D: optical

Components 4 (quadruple)

Component IDs AB

Separation 7.3″

Companion Mag 5.0

Companion Sp B2V

Position Angle 132°

Star Colors A: Blue B: Blue

Discoverer STF 919

Notes

Triple system with HR 2357 and 2358. Combined mag., color 3.74V, -0.15(B-V), all Be stars. AB, 17000y; AC, sep. 10", | 29000y. Component D, 12.2v at 26" from A. Uncertain which of components A,B,C, HR 2356,7,8 is the light variable | NSV 2977, for which the mag. 3.75V is a blend of all three.

Separation over time

Measured 1822 → 2022 (200 y)

Separation drift 6.9" → 7.3" (+0.40")

Rate +0.0020" / y

PA drift 130° → 132° (+2°, +0.010°/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.