Sirius

Sirius
Location of Sirius (circled)
Observation data
Epoch J2000.0      Equinox ICRS
Constellation Canis Major
Pronunciation /ˈsɪriəs/[1]
Sirius A
Right ascension 06h 45m 08.917s[2]
Declination −16° 42′ 58.02″[2]
Apparent magnitude (V) −1.46[3]
Sirius B
Right ascension 06h 45m 09.0s[4]
Declination −16° 43′ 06″[4]
Apparent magnitude (V) 8.44[5]
Characteristics
Sirius A
Evolutionary stage Main sequence
Spectral type A0mA1 Va[6]
U−B colour index −0.05[3]
B−V colour index +0.00[3]
Sirius B
Evolutionary stage White dwarf
Spectral type DA2[5]
U−B colour index −1.04[7]
B−V colour index −0.03[7]
Astrometry
Radial velocity (Rv)−5.50[8] km/s
Sirius A
Proper motion (μ) RA: −546.01 mas/yr[9]
Dec.: −1,223.07 mas/yr[9]
Parallax (π)378.9±1.4 mas[10]
Distance8.61 ± 0.03 ly
(2.639 ± 0.010 pc)
Absolute magnitude (MV)+1.43[11]
Sirius B
Proper motion (μ) RA: −461.571 mas/yr[12]
Dec.: −914.520 mas/yr[12]
Parallax (π)378.9±1.4 mas[10]
Distance8.61 ± 0.03 ly
(2.639 ± 0.010 pc)
Absolute magnitude (MV)+11.18[7]
Orbit[10]
Primaryα Canis Majoris A
Companionα Canis Majoris B
Period (P)50.1284±0.0043 yr
Semi-major axis (a)7.4957±0.0025″
Eccentricity (e)0.59142±0.00037
Inclination (i)136.336±0.040°
Longitude of the node (Ω)45.400±0.071°
Periastron epoch (T)1994.5715±0.0058
Argument of periastron (ω)
(secondary)		149.161±0.075°
Details
Sirius A
Mass2.063±0.023[10] M☉
Radius1.713±0.009[13] R☉
Luminosity24.7±0.7[13] L☉
Surface gravity (log g)4.33[14] cgs
Temperature9,845±64[13] K
Metallicity [Fe/H]0.50[15] dex
Rotational velocity (v sin i)16[16] km/s
Age242±5[10] Myr
Sirius B
Mass1.018±0.011[10] M☉
Radius0.008098±0.6%[10] R☉
Radius5,634±33.80 km
Luminosity0.02448±1.3%[10] L☉
Surface gravity (log g)8.57[17] cgs
Temperature25,000±200[18] K
Age228+10
−8[10] Myr
Other designations
Dog Star, Aschere, Canicula, Al Shira, Sothis,[19] Alhabor,[20] Mrgavyadha, Lubdhaka,[21] Tenrōsei,[22] α Canis Majoris (α CMa), 9 Canis Majoris (9 CMa), HD 48915, HR 2491, BD−16°1591, GJ 244, LHS 219, ADS 5423, LTT 2638, HIP 32349[23]
Sirius B: EGGR 49, WD 0642-166, GCTP 1577.00[24]
Database references
SIMBADA
B

Sirius is the brightest star in the night sky. Its name is derived from the Greek word Σείριος (Latin script: Seirios; lit. 'glowing' or 'scorching'). The star is designated α Canis Majoris, Latinized to Alpha Canis Majoris, and abbreviated α CMa or Alpha CMa. With a visual apparent magnitude of −1.46, Sirius is almost twice as bright as Canopus, the next brightest star. Sirius is a binary star consisting of a main-sequence star of spectral type A0 or A1, termed Sirius A, and a faint white dwarf companion of spectral type DA2, termed Sirius B. The distance between the two varies between 8.2 and 31.5 astronomical units as they orbit every 50 years.[25]

Sirius appears bright because of its intrinsic luminosity and its proximity to the Solar System. At a distance of 2.64 parsecs (8.6 ly), the Sirius system is one of Earth's nearest neighbours. Sirius is gradually moving closer to the Solar System and it is expected to increase in brightness slightly over the next 60,000 years to reach a peak magnitude of −1.68. Coincidentally, at about the same time, Sirius will take its turn as the southern Pole Star, around the year 66,270 AD. In that year, Sirius will come to within 1.6 degrees of the south celestial pole. This is due to axial precession and proper motion of Sirius itself which moves slowly in the SSW direction, so it will be visible from the southern hemisphere only. [26] After that time, its distance will begin to increase, and it will become fainter, but it will continue to be the brightest star in the Earth's night sky for approximately the next 210,000 years, at which point Vega, another A-type star that is intrinsically more luminous than Sirius, becomes the brightest star.[27]

Sirius A is about twice as massive as the Sun (M☉) and has an absolute visual magnitude of +1.43. It is 25 times as luminous as the Sun,[18] but has a significantly lower luminosity than other bright stars such as Canopus, Betelgeuse, or Rigel. The system is between 200 and 300 million years old.[18] It was originally composed of two bright bluish stars. The initially more massive of these, Sirius B, consumed its hydrogen fuel 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.[18]

Sirius is colloquially known as the "Dog Star", reflecting its prominence in its constellation, Canis Major (the Greater Dog).[19] 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, mostly in the Southern Hemisphere, the star marked winter and was an important reference for their navigation around the Pacific Ocean.

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  2. ^ a b Fabricius, C.; Høg, E.; Makarov, V.V.; Mason, B.D.; Wycoff, G.L.; Urban, S.E. (2002). "The Tycho double star catalogue". Astronomy and Astrophysics. 384: 180–189. Bibcode:2002A&A...384..180F. doi:10.1051/0004-6361:20011822.
  3. ^ a b c Cite error: The named reference Hoffleit1991 was invoked but never defined (see the help page).
  4. ^ a b Gianninas, A.; Bergeron, P.; Ruiz, M.T. (2011). "A spectroscopic survey and analysis of bright, hydrogen-rich white dwarfs". The Astrophysical Journal. 743 (2): 138. arXiv:1109.3171. Bibcode:2011ApJ...743..138G. doi:10.1088/0004-637X/743/2/138. S2CID 119210906.
  5. ^ a b Holberg, J.B.; Oswalt, T.D.; Sion, E.M.; Barstow, M.A.; Burleigh, M.R. (2013). "Where are all the Sirius-like binary systems?". Monthly Notices of the Royal Astronomical Society. 435 (3): 2077–2091. arXiv:1307.8047. Bibcode:2013MNRAS.435.2077H. doi:10.1093/mnras/stt1433. S2CID 54551449.
  6. ^ Gray, R.O.; Corbally, C.J.; Garrison, R.F.; McFadden, M.T.; Robinson, P.E. (2003). "Contributions to the Nearby Stars (NStars) Project: Spectroscopy of stars earlier than M0 within 40 parsecs: The Northern Sample. I". Astronomical Journal. 126 (4): 2048–2059. arXiv:astro-ph/0308182. Bibcode:2003AJ....126.2048G. doi:10.1086/378365. S2CID 119417105.
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  8. ^ Gontcharov, G.A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. ISSN 1063-7737. S2CID 119231169.
  9. ^ van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.
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  11. ^ Malkov, O. Yu. (December 2007). "Mass-luminosity relation of intermediate-mass stars". Monthly Notices of the Royal Astronomical Society. 382 (3): 1073–1086. Bibcode:2007MNRAS.382.1073M. doi:10.1111/j.1365-2966.2007.12086.x.
  12. ^ Vallenari, A.; et al. (Gaia collaboration) (2023). "Gaia Data Release 3. Summary of the content and survey properties". Astronomy and Astrophysics. 674: A1. arXiv:2208.00211. Bibcode:2023A&A...674A...1G. doi:10.1051/0004-6361/202243940. S2CID 244398875. Gaia DR3 record for this source at VizieR.
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  18. ^ a b c d Cite error: The named reference Liebert2005 was invoked but never defined (see the help page).
  19. ^ a b Cite error: The named reference Allen1899 was invoked but never defined (see the help page).
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  26. ^ Sirius is a future southern Pole Star. 2023-02-11.
  27. ^ Tomkin, Jocelyn (April 1998). "Once and future celestial kings". Sky and Telescope. 95 (4): 59–63. Bibcode:1998S&T....95d..59T.
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