When is the best time to observe Sirius?

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

Where is Sirius located in the sky?

Sirius lies in the constellation Canis Major at right ascension 06h 45m and declination -16° 43′.

What telescope do I need to split Sirius?

Splitting Sirius requires an aperture of roughly 490 mm or larger — the components are separated by about 11.1″ at magnitudes near -1.5. The companion is about 9.9 magnitudes fainter, so glare from the primary — not separation — sets the minimum aperture. Larger apertures and steady seeing help resolve the pair cleanly.

Sirius — Double Star in Canis Major

HIP 32349; Alpha Canis Majoris; 9 Canis Majoris

Magnitude -1.5^m DoubleStar Canis Major (CMa) Visible

Star Map + List + Plan

About Sirius

Description

Sirius is the brightest star in the night sky at magnitude -1.46, a white main-sequence star of spectral type A1V located only 8.6 light-years from Earth. It is a binary system — Sirius B, its white dwarf companion, orbits every 50 years and was one of the first white dwarfs discovered. The primary has a luminosity of about 25 times solar and a surface temperature of 9,940 K.

Observing Tips

Unmistakable as the brightest star in the sky, Sirius blazes in Canis Major southeast of Orion. Follow Orion's Belt downward-left to find it. Its brilliance causes it to twinkle dramatically in many colors when low on the horizon — an atmospheric effect, not intrinsic. Sirius B requires at least an 8-inch telescope at high magnification during periods of good seeing, and is easiest when near maximum separation from the primary. Best observed December through March.

History

Sirius has been revered since antiquity. The ancient Egyptians based their calendar on its heliacal rising, which coincided with the annual flooding of the Nile. The name comes from the Greek 'Seirios' meaning 'scorching.' The 'Dog Days' of summer refer to the period when Sirius rises with the Sun. Its companion Sirius B was predicted by Friedrich Bessel in 1844 and first observed by Alvan Graham Clark in 1862.

Fun Facts

Sirius is approaching the Sun and will brighten slightly over the next 60,000 years before beginning to recede. Ancient records describe Sirius as red, which has puzzled astronomers — the star is clearly white today, and no known mechanism could change its color in just 2,000 years.

Observe

1Physical Properties

Magnitude -1.46

Spectral Type A0mA1Va

Star Color Blue-white (B-V 0.00)

Temperature 9984 K

Radius 1.6 R☉

Distance 9 ly

2Position & Identifiers

RA 06h 45m 08.9s

Dec -16° 42' 58.0"

Constellation Canis Major (CMa)

HR 2491

HIP 32349

HD 48915

SAO 151881

Bayer Alpha

Flamsteed 9 CMa

Double Cat 5423

SIMBAD Wikipedia

3How easy to split?

Primary -1.5 mag Companion 8.4 mag Separation 11.1″

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

Easy Medium Hard Very hard Impossible

Bortle 3 = rural · 4 = outer suburbs · 5 = suburbs

To reach "Medium" at Bortle 3, you'd need at least a 490 mm reflector.

4Visibility

Set a location in User Settings to see visibility data.

Best season Nov – Jan (peak: Dec)

5Multiple Star System Quadruple

Components 4 (quadruple)

Component IDs AB

Separation 11.1″

Companion Mag 8.4

Companion Sp DA2

Position Angle 59°

Star Colors A: Blue-white

Discoverer AGC 1

Notes

AB -1.46 A1V, 8.49 A1V, 50.090y, a = 7.500" or 49.94y, a = 7.62". D, 14.0v at 32" from A. C, companion to B at 1.4" | suspected but not confirmed. B is first white dwarf ever discovered; predicted by Bessel (1844) on basis of orbital | motion of Sirius, it was first seen by Alvan Clark in 1862, and its peculiar high temperature, small size and great | density established by W. Adams in 1925.

Separation over time

Period: 50.1 y Eccentricity: 0.591 Now: 11.1", PA 56° -1.17" in 5 years

Apparent separation over time, computed from ORB6 orbital elements. Steep curves indicate fast-changing pairs — catch them while they're splittable.

Eyepiece View

Telescope Eyepiece

80x Dawes: 1.9″ TFOV: 0.6°

Seeing

Scale Realistic = true angular size

A: -1.5 · B: 8.4 · Sep: 11.1″ · PA: 59° · N up, E right

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

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Size Comparison

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Spectral Classification

Hertzsprung-Russell Diagram

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

Stellar Lifecycle

Blackbody Spectrum

Stellar Absorption Spectrum

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

Stellar Fusion

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15Stellar Notes

Spectroscopic Binary

50.04y D, K 2.4k/s, V0 -7.6k/s, asini 487.

Color

Color excess E(B-V) = -0.03.

Group/Cluster

Sirius group; UMa stream.

Spectral

Cadmium discovered in spectra from COPERNICUS. Iron overabundant by a factor of 5 in comparison with Sun and titanium by | a factor of 2. Possibility that the atmosphere of Sirius A polluted by material ejected from Sirius B. Weak magnetic | field. Barium abundance greater than solar abundance by about 1.76. Also classified A/A0/A1.

Dynamical

0.376".

Alternative Names

SIRIUS; Canicula; Dog Star; Aschere.

Remarks

Diam. = 0.00560 - 0.00589".