Sirius

Hubble Space Telescope image of Sirius A and Sirius B. The white dwarf can be seen to the lower left. The diffraction spikes and concentric rings are instrumental effects.
Sirius (bottom) and the constellation Orion (right). The three brightest stars in this image—Sirius, Betelgeuse (top right) and Procyon (top left)—form the Winter Triangle. The bright star at top center is Alhena, which forms a cross-shaped asterism with the Winter Triangle.
The orbit of Sirius B around A as seen from Earth (slanted ellipse). The wide horizontal ellipse shows the true shape of the orbit (with an arbitrary orientation) as it would appear if viewed straight on.
A Chandra X-ray Observatory image of the Sirius star system, where the spike-like pattern is due to the support structure for the transmission grating. The bright source is Sirius B. Credit: NASA/SAO/CXC
Comparison of Sirius A and the Sun, to scale and relative surface brightness
Size comparison of Sirius B and Earth
A bust of Sopdet, Egyptian goddess of Sirius and the fertility of the Nile, syncretized with Isis and Demeter
Sirius midnight culmination at New Year 2022 local solar time
Yoonir, symbol of the universe in Serer religion

Brightest star in the night sky.

- Sirius
Hubble Space Telescope image of Sirius A and Sirius B. The white dwarf can be seen to the lower left. The diffraction spikes and concentric rings are instrumental effects.

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An artist's impression of Sirius A and Sirius B, a binary star system. Sirius A, an A-type main-sequence star, is the larger of the two.

A-type main-sequence star

Main-sequence (hydrogen-burning) star of spectral type A and luminosity class V (five).

Main-sequence (hydrogen-burning) star of spectral type A and luminosity class V (five).

An artist's impression of Sirius A and Sirius B, a binary star system. Sirius A, an A-type main-sequence star, is the larger of the two.
The Morgan-Keenan spectral classification

Bright and nearby examples are Altair (A7 V), Sirius A (A1 V), and Vega (A0 V).

Sirius A, the brightest star in the night sky, lies in Canis Major.

Canis Major

Constellation in the southern celestial hemisphere.

Constellation in the southern celestial hemisphere.

Sirius A, the brightest star in the night sky, lies in Canis Major.
Canis Major as depicted on the Manuchihr Globe made in Mashhad 1632-33 AD. Adilnor Collection, Sweden.
Canis Major, observed above Kuantan (north is towards top right)
The stars of Canis Major as they can be seen by the naked eye; lines have been added for clarity.
Canis Major as depicted in Urania's Mirror, a set of constellation cards published in London c.1825. Next to it are Lepus and Columba (partly cut off).
Very Large Telescope image of the surroundings of VY Canis Majoris
ESO 489-056 is an irregular dwarf galaxy, located 16 million light-years distant.

Canis Major contains Sirius, the brightest star in the night sky, known as the "dog star".

Diffuse reflection on sphere and flat disk

Absolute magnitude

Measure of the luminosity of a celestial object, on an inverse logarithmic astronomical magnitude scale.

Measure of the luminosity of a celestial object, on an inverse logarithmic astronomical magnitude scale.

Diffuse reflection on sphere and flat disk
Brightness with phase for diffuse reflection models. The sphere is 2/3 as bright at zero phase, while the disk can't be seen beyond 90 degrees.
Asteroid 1 Ceres, imaged by the Dawn spacecraft at phase angles of 0°, 7° and 33°. The left image at 0° phase angle shows the brightness surge due to the opposition effect.
Phase integrals for various values of G

For comparison, Sirius has an absolute magnitude of only 1.4, which is still brighter than the Sun, whose absolute visual magnitude is 4.83.

Image of Sirius A and Sirius B taken by the Hubble Space Telescope. Sirius B, which is a white dwarf, can be seen as a faint point of light to the lower left of the much brighter Sirius A.

White dwarf

Stellar core remnant composed mostly of electron-degenerate matter.

Stellar core remnant composed mostly of electron-degenerate matter.

Image of Sirius A and Sirius B taken by the Hubble Space Telescope. Sirius B, which is a white dwarf, can be seen as a faint point of light to the lower left of the much brighter Sirius A.
A comparison between the white dwarf IK Pegasi B (center), its A-class companion IK Pegasi A (left) and the Sun (right). This white dwarf has a surface temperature of 35,500 K.
The white dwarf cooling sequence seen by ESA's Gaia mission
Artist's impression of the WD J0914+1914 system.
Internal structures of white dwarfs. To the left is a newly formed white dwarf, in the center is a cooling and crystallizing white dwarf, and the right is a black dwarf.
Artist's impression of debris around a white dwarf
Comet falling into white dwarf (artist's impression)
The merger process of two co-orbiting white dwarfs produces gravitational waves
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The white dwarf companion of Sirius, Sirius B, was next to be discovered.

Sirius is the fixed star with the greatest apparent magnitude and one which is almost non-variable. The Pleiades, a key feature of Taurus shown across Orion in the same photograph also experience an annual period of visibility ("rising and setting").

Heliacal rising

The heliacal rising or star rise of a star occurs annually, or the similar phenomenon of a planet, when it first becomes visible above the eastern horizon at dawn just before sunrise (thus becoming "the morning star"), after it has spent a season behind the sun rendering it invisible.

The heliacal rising or star rise of a star occurs annually, or the similar phenomenon of a planet, when it first becomes visible above the eastern horizon at dawn just before sunrise (thus becoming "the morning star"), after it has spent a season behind the sun rendering it invisible.

Sirius is the fixed star with the greatest apparent magnitude and one which is almost non-variable. The Pleiades, a key feature of Taurus shown across Orion in the same photograph also experience an annual period of visibility ("rising and setting").

Historically, the most important such rising is that of Sirius, which was an important feature of the Egyptian calendar and astronomical development.

A plane flying past a radar station: the plane's velocity vector (red) is the sum of the radial velocity (green) and the tangential velocity (blue).

Radial velocity

Observer is the rate of change of the distance or range between the two points.

Observer is the rate of change of the distance or range between the two points.

A plane flying past a radar station: the plane's velocity vector (red) is the sum of the radial velocity (green) and the tangential velocity (blue).
Diagram showing how an exoplanet's orbit changes the position and velocity of a star as they orbit a common center of mass
The radial velocity method to detect exoplanets

William Huggins ventured in 1868 to estimate the radial velocity of Sirius with respect to the Sun, based on observed redshift of the star's light.

The festival of the Nile as depicted in Norden's Voyage d'Egypte et de Nubie

Flooding of the Nile

Important natural cycle in Egypt since ancient times.

Important natural cycle in Egypt since ancient times.

The festival of the Nile as depicted in Norden's Voyage d'Egypte et de Nubie

This cycle was so consistent that the Egyptians timed its onset using the heliacal rising of Sirius, the key event used to set their calendar.

Binary system of two stars

Binary star

System of two stars that are gravitationally bound to and in orbit around each other.

System of two stars that are gravitationally bound to and in orbit around each other.

Binary system of two stars
Edge-on disc of gas and dust present around the binary star system HD 106906
Algol B orbits Algol A. This animation was assembled from 55 images of the CHARA interferometer in the near-infrared H-band, sorted according to orbital phase.
Artist's conception of a cataclysmic variable system
Artist's impression of the binary star system AR Scorpii
Artist rendering of plasma ejections from V Hydrae
Artist's impression of the sight from a (hypothetical) moon of planet HD 188753 Ab (upper left), which orbits a triple star system. The brightest companion is just below the horizon.
Schematic of a binary star system with one planet on an S-type orbit and one on a P-type orbit
The two visibly distinguishable components of Albireo
Luhman 16, the third closest star system, contains two brown dwarfs.
Planet Lost in the Glare of Binary Stars (illustration)

Examples of binaries are Sirius, and Cygnus X-1 (Cygnus X-1 being a well-known black hole).

The constellation Carina with Canopus towards the right (west)

Canopus

Brightest star in the southern constellation of Carina and the second-brightest star in the night sky.

Brightest star in the southern constellation of Carina and the second-brightest star in the night sky.

The constellation Carina with Canopus towards the right (west)
Wide angle view showing Canopus and other prominent stars with the Milky Way
Canopus is the brightest star in the constellation of Carina (top).
Averroes, who used his 1153 observation of Canopus in Marrakesh while the star was invisible in his native Spain as an argument that the earth is round.
Canopus-class battleship HMS Glory

With a visual apparent magnitude of −0.74, it is outshone only by Sirius.

Asteroid 65 Cybele and two stars, with their magnitudes labeled

Apparent magnitude

Measure of the brightness of a star or other astronomical object observed from Earth.

Measure of the brightness of a star or other astronomical object observed from Earth.

Asteroid 65 Cybele and two stars, with their magnitudes labeled
Image of 30 Doradus taken by ESO's VISTA. This nebula has a visual magnitude of 8.
Graph of relative brightness versus magnitude

The brightest astronomical objects have negative apparent magnitudes: for example, Venus at −4.2 or Sirius at −1.46.