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Sirius
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Sirius A / B
The position of Sirius.
Observation data
Epoch J2000.0 Equinox J2000.0 (ICRS)
Constellation
Canis Major
Pronunciation
/'s?ri?s/
Right ascension
06h 45m 08.9173s
Declination
-16° 42' 58.017?
Apparent magnitude (V)
-1.46 (A) / 8.30 (B)
Characteristics
Spectral type
A1V (A) / DA2 (B)
U-B color index
-0.05 (A) / -1.04 (B)
B-V color index
0.01 (A) / -0.03 (B)
Astrometry
Radial velocity (Rv)
-7.6 km/s
Proper motion (µ)
RA: -546.05 mas/yr
Dec.: -1223.14 mas/yr
Parallax (p)
379.21 ± 1.58 mas
Distance
8.6 ± 0.04 ly
(2.64 ± 0.01 pc)
Absolute magnitude (MV)
1.42 (A) / 11.18 (B)
Orbit
Companion
a CMa B
Period (P)
50.090 ± 0.055 yr
Semimajor axis (a)
7.50 ± 0.04"
Eccentricity (e)
0.5923 ± 0.0019
Inclination (i)
136.53 ± 0.43°
Longitude of the node (O)
44.57 ± 0.44°
Periastron epoch (T)
1894.130 ± 0.015
Argument of periastron (?)
(secondary)
147.27 ± 0.54°
Details
a CMa A
Mass
2.02 M?
Radius
1.711 R?
Luminosity
25.4 L?
Surface gravity (log g)
4.33
Temperature
9,940 K
Metallicity
0.50 dex
Rotation
16 km/s
Age
2–3 × 108 years
a CMa B
Mass
0.978 M?
Radius
0.0084 ± 3% R?
Luminosity
0.026 L?
Surface gravity (log g)
8.57
Temperature
25,200 K
Other designations
System: Dog Star, Aschere, Canicula, Al Shira, Sothis,Mrgavyadha, Lubdhaka, Tenrosei, a Canis Majoris (a CMa), 9 Canis Majoris (9 CMa), HD 48915, HR 2491, BD -16°1591, GCTP 1577.00 A/B, GJ 244 A/B, LHS 219, ADS 5423, LTT 2638, HIP 32349.
B: EGGR 49, WD 0642-166.
Sirius is the brightest star in the night sky. With a visual apparent magnitude of -1.46, it is almost twice as bright as Canopus, the next brightest star. The name "Sirius" is derived from the Ancient Greek: Se????? Seirios ("glowing" or "scorcher"). The star has the Bayer designation Alpha Canis Majoris (a CMa). What the naked eye perceives as a single star is actually a binary star system, consisting of a white main sequence star of spectral type A1V, termed Sirius A, and a faint white dwarf companion of spectral type DA2, called Sirius B. The distance separating Sirius A from its companion varies between 8.1 and 31.5 AU.Sirius appears bright because of both its intrinsic luminosity and its proximity to Earth. At a distance of 2.6 parsecs (8.6 ly), the Sirius system is one of Earth's near neighbors; for Northern-hemisphere observers between 30 degrees and 73 degrees of latitude (including almost all of Europe and North America), it is the closest star (after the Sun) that can be seen with a naked eye. Sirius A is about twice as massive as the Sun and has an absolute visual magnitude of 1.42. It is 25 times more luminous than the Sun but has a significantly lower luminosity than other bright stars such as Canopus or Rigel. The system is between 200 and 300 million years old. It was originally composed of two bright bluish stars. The more massive of these, Sirius B, consumed its resources and became a red giant before shedding its outer layers and collapsing into its current state as a white dwarf around 120 million years ago.Sirius is also known colloquially as the "Dog Star", reflecting its prominence in its constellation, Canis Major (Greater Dog). The heliacal rising of Sirius marked the flooding of the Nile in Ancient Egypt and the "dog days" of summer for the ancient Greeks, while to the Polynesians it marked winter and was an important star for navigation around the Pacific Ocean.
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