When is the best time to observe Aludra?

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

Where is Aludra located in the sky?

Aludra lies in the constellation Canis Major at right ascension 07h 24m and declination -29° 18′.

What telescope do I need to split Aludra?

Splitting Aludra requires an aperture of roughly 60 mm or larger — the components are separated by about 177.0″ at magnitudes near 2.5. The companion is about 4.3 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Aludra — Double Star in Canis Major

HIP 35904; Eta Canis Majoris; 31 Canis Majoris

Observable Double Star Good (48/100)

Sep: 177.0", Companion: mag 6.8

Magnitude 2.5^m DoubleStar Canis Major (CMa) Visible

Star Map + List + Plan

About Aludra

Description

Aludra is a blue supergiant of spectral type B5Ia at magnitude 2.45 in Canis Major. Located about 2,000 light-years from Earth, it is one of the most distant and luminous stars visible to the naked eye, with a luminosity of roughly 105,000 times solar. Aludra marks the tail of the Great Dog.

Observing Tips

Aludra lies in the tail of Canis Major, south-southeast of Sirius. It appears as a blue-white star of moderate brightness. Despite its modest appearance, it is intrinsically enormously luminous. Best observed January through March.

History

The name Aludra comes from the Arabic 'al-'udhra,' meaning 'the virginity' or 'the maiden.' Despite its great distance, Aludra is bright enough to be easily visible because of its extraordinary intrinsic luminosity. It is a massive star approaching the end of its life.

Fun Facts

Aludra is a supernova candidate — at roughly 20 solar masses, it will exhaust its nuclear fuel within a few million years and end in a catastrophic explosion. At 2,000 light-years, any supernova would create a spectacular display visible in daylight but pose no danger to Earth.

Observe

1Physical Properties

Magnitude 2.45

Spectral Type B5Ia supergiant

Star Color Blue-white (B-V -0.08)

Distance 1,989 ly

2Position & Identifiers

RA 07h 24m 05.7s

Dec -29° 18' 11.0"

Constellation Canis Major (CMa)

HR 2827

HIP 35904

HD 58350

SAO 173651

Bayer Eta

Flamsteed 31 CMa

SIMBAD Wikipedia

3How easy to split?

Primary 2.5 mag Companion 6.8 mag Separation 177.0″

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

Set a location in User Settings to see visibility data.

Best season Dec – Feb (peak: Jan)

5Multiple Star System

Separation 177.0″

Companion Mag 6.8

Companion Sp A0V

Position Angle 287°

Star Colors A: Blue-white B: Yellow

Discoverer SMY 2

Notes

Companion is A0V, optical, vsini =<54k/s.

Separation over time

Measured 1833 → 2020 (187 y)

Separation drift 169.0" → 177.0" (+8.00")

Rate +0.0428" / y

PA drift 285° → 287° (+2°, +0.011°/y)

Apparent motion is significant on a human timescale — worth revisiting in a decade.

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.