When is the best time to observe 3 Monocerotis?

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

Where is 3 Monocerotis located in the sky?

3 Monocerotis lies in the constellation Monoceros at right ascension 06h 02m and declination -10° 36′.

What telescope do I need to split 3 Monocerotis?

Splitting 3 Monocerotis requires an aperture of roughly 100 mm or larger — the components are separated by about 2.0″ at magnitudes near 5.0. The companion is about 3.0 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

3 Monocerotis — Double Star in Monoceros

Observable Double Star Good (49/100)

Sep: 2.0", Companion: mag 8.0

Magnitude 5.0^m DoubleStar Monoceros (Mon) Visible

Star Map + List + Plan

Observe

1Physical Properties

Magnitude 4.95

Spectral Type B5III giant

Star Color Blue-white (B-V -0.12)

Distance 1,087 ly

2Position & Identifiers

RA 06h 01m 50.4s

Dec -10° 35' 53.0"

Constellation Monoceros (Mon)

HR 2128

HIP 28574

HD 40967

SAO 151037

Flamsteed 3 Mon

Double Cat 4615

SIMBAD

3How easy to split?

Primary 5.0 mag Companion 8.0 mag Separation 2.0″

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

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

Separation 2.0″

Companion Mag 8.0

Position Angle 354°

Star Colors A: Blue-white B: Yellow-white

Discoverer BU 16

Notes

Binary.

Separation over time

Measured 1871 → 2016 (145 y)

Separation drift 1.8" → 2.0" (+0.20")

Rate +0.0014" / y

PA drift 356° → 354° (-2°, -0.014°/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.