When is the best time to observe 15 Monocerotis?

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

Where is 15 Monocerotis located in the sky?

15 Monocerotis lies in the constellation Monoceros at right ascension 06h 41m and declination +09° 54′.

What telescope do I need to split 15 Monocerotis?

Splitting 15 Monocerotis requires an aperture of roughly 100 mm or larger — the components are separated by about 3.0″ at magnitudes near 4.7. The companion is about 3.1 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

15 Monocerotis — Double Star in Monoceros

Observable Double Star Good (52/100)

Sep: 3.0", Companion: mag 7.8

Magnitude 4.7^m DoubleStar Monoceros (Mon) Visible

Star Map + List + Plan

Observe

1Physical Properties

Magnitude 4.66

Range 4.62 - 4.68

Variable Type IA:

Spectral Type O7V((f))

Star Color Blue (B-V -0.25)

2Position & Identifiers

RA 06h 40m 58.7s

Dec +09° 53' 44.0"

Constellation Monoceros (Mon)

HR 2456

HIP 31978

HD 47839

SAO 114258

Flamsteed 15 Mon

Variable ID S Mon

Double Cat 5322

SIMBAD

3How easy to split?

Primary 4.7 mag Companion 7.8 mag Separation 3.0″

Sign in and configure your equipment and default location to see a personalized row.

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	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)

5Multiple Star System 13 components E,I: optical

Components 13

Component IDs AB

Separation 3.0″

Companion Mag 7.8

Companion Sp B1:V

Position Angle 214°

Star Colors A: Blue B: Blue

Discoverer STF 950

Notes

AB binary, 4.8 Oe5, 7.6 B7; C, 9.9v B8V at 17", physical, vsini 141k/s; D, 9.7v A6III at 41", physical, vsini 115k/s; | E1 the brighter component of E, B5V at 74", probably optical, vsini 253k/s; E2, A0V, vsini 132k/s.

Separation over time

Measured 1825 → 2018 (193 y)

Separation drift 2.7" → 3.0" (+0.30")

Rate +0.0016" / y

PA drift 205° → 214° (+9°, +0.047°/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.

Eyepiece View

Telescope Eyepiece

Log in to set your own equipment

80x Dawes: 1.9″ TFOV: 0.6°

Seeing

Scale Realistic = true angular size

A: 4.7 · B: 7.8 · Sep: 3.0″ · PA: 214° · N up, E right

Resolved · Rayleigh: 2.3″ · Dawes: 1.9″ · Eff: 2.3″

Explore

6

Size Comparison

Querying VizieR for stellar data…

7

Compare Stars

Compare with another star

8

Spectral Classification

9

Hertzsprung-Russell Diagram

Loading HR diagram…

Read: The Hertzsprung-Russell Diagram — Reading Stars Like a Map

10

Stellar Lifecycle

11

Blackbody Spectrum

12

Stellar Absorption Spectrum

Simulated absorption spectrum based on spectral type. Hover over lines to identify elements.

13

Stellar Fusion

Discover

14Stellar Notes

Variable Star

ADS 5322A, Ia? 4.62 - 4.67V. R-I also found at -0.11.

Color

Color excess E(B-V) = +0.07.

Group/Cluster

In cluster NGC 2264 #131; HII reg. S273; Mon OB1; T-Tauri assoc., Mon T1. The cluster appears to be the nucleus of the | association. In region of neutral hydrogen. Ionized Mon OB1 region probably excited by S Mon. The electron density of | the HII region increases toward the center of the cluster. (Note that OB associations MonI = IIMon = Mon OB1 and MonII = | IMon = OB2. In conversions from the earlier designations to OB1 and OB2 these groups have occasionally been | interchanged; however, they may be related.)

Spectral

Also classified O8III((f)). uv 1240 absorption strong.

Dynamical

0.005".