When is the best time to observe Theta Muscae?

Theta Muscae is best observed from March through May, with peak visibility during April when it transits around midnight in the Northern Hemisphere.

Where is Theta Muscae located in the sky?

Theta Muscae lies in the constellation Musca at right ascension 13h 08m and declination -65° 18′.

What telescope do I need to split Theta Muscae?

Splitting Theta Muscae requires an aperture of roughly 80 mm or larger — the components are separated by about 5.2″ at magnitudes near 5.5. Larger apertures and steady seeing help resolve the pair cleanly.

Theta Muscae — Double Star in Musca

Observable Double Star Good (52/100)

Sep: 5.2", Companion: mag 7.5

Wolf-Rayet

Late-stage massive star with a dense stellar wind; radius is taken from published spectral models rather than estimated from spectral class.

Read: Wolf-Rayet Stars — The Shortest, Fiercest Lives in the Galaxy

Magnitude 5.5^m DoubleStar Musca (Mus) Visible

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Observe

1Physical Properties

Magnitude 5.51

Range 5.50 - 5.52

Period 18.3 days

Variable Type E/WR

Spectral Type B0Ia+WC5: Wolf-Rayet

Late-stage massive star with a dense stellar wind; radius is taken from published spectral models rather than estimated from spectral class.

Star Color Blue-white (B-V -0.02)

2Position & Identifiers

RA 13h 08m 07.0s

Dec -65° 18' 23.0"

Constellation Musca (Mus)

HR 4952

HIP 64094

HD 113904

SAO 252162

Bayer Theta

Variable ID The Mus

SIMBAD

3How easy to split?

Primary 5.5 mag Companion 7.6 mag Separation 5.2″

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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 Mar – May (peak: Apr)

5Light Curve

6Multiple Star System

Separation 5.2″

Companion Mag 7.5

Companion Sp WC5:

Position Angle 184°

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

Discoverer RMK 16

Notes

CPM. vsini of secondary 110k/s.

Separation over time

Measured 1826 → 2024 (198 y)

Separation drift 3.3" → 5.2" (+1.90")

Rate +0.0096" / y

PA drift 191° → 184° (-7°, -0.035°/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.

Eyepiece View

Telescope Eyepiece

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80x Dawes: 1.9″ TFOV: 0.6°

Seeing

Scale Realistic = true angular size

A: 5.5 · B: 7.5 · Sep: 5.2″ · PA: 184° · N up, E right

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

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7

Size Comparison

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8

Compare Stars

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9

Spectral Classification

10

Hertzsprung-Russell Diagram

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

11

Stellar Lifecycle

12

Blackbody Spectrum

13

Stellar Absorption Spectrum

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

14

Stellar Fusion

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15Stellar Notes

Variable Star

E + WR 5.50 - 5.52V, 18.341d; UV, var. 1.5d.

Spectroscopic Binary

18.341d, K 173k/s, msin3i 0.366, asini 43.6. Possibly third, unseen, companion orbiting the WR star.

Group/Cluster

Nebula R43.

Spectral

H alpha emission star. One of only four WR stars bright enough to have been observed spectroscopically in UV by | COPERNICUS. Brightest of group of emission stars surrounding m Cen = HR 5041 in region of bright and dark neb. UV | spectrum dominated by supergiant companions. Variable emission lines.