A report on Sirius and Alpha Centauri

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.
Alpha Centauri is the brightest object in the constellation of Centaurus (top left).
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.
Apparent and true orbits of Alpha Centauri. The A component is held stationary, and the relative orbital motion of the B component is shown. The apparent orbit (thin ellipse) is the shape of the orbit as seen by an observer on Earth. The true orbit is the shape of the orbit viewed perpendicular to the plane of the orbital motion. According to the radial velocity versus time, the radial separation of A and B along the line of sight had reached a maximum in 2007, with B being further from Earth than A. The orbit is divided here into 80 points: each step refers to a timestep of approx. 0.99888 years or 364.84 days.
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.
The relative sizes and colours of stars in the Alpha Centauri system, compared to the Sun
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
Relative positions of Sun, Alpha Centauri AB and Proxima Centauri. Grey dot is projection of Proxima Centauri, located at the same distance as Alpha Centauri AB.
Comparison of Sirius A and the Sun, to scale and relative surface brightness
The two bright stars at the lower right are Alpha (right) and Beta Centauri (left, above antenna). A line drawn through them points to the four bright stars of the Southern Cross, just to the right of the dome of the Danish 1.54 m telescope at La Silla Observatory in Chile.
Size comparison of Sirius B and Earth
Alpha Centauri AB taken in daylight by holding a Canon Powershot S100 in line with the eyepiece of a 110-mm refractor. The photo is one of the best frames of a video. The double star is clearly visible.
A bust of Sopdet, Egyptian goddess of Sirius and the fertility of the Nile, syncretized with Isis and Demeter
View of Alpha Centauri from the Digitized Sky Survey-2
Alpha Centauri A is of the same stellar type G2 as the Sun, while Alpha Centauri B is a K1-type star.
Sirius midnight culmination at New Year 2022 local solar time
Closest stars to the Sun
Yoonir, symbol of the universe in Serer religion
Distances of the nearest stars from 20,000 years ago until 80,000 years in the future
Animation showing motion of Alpha Centauri through the sky. (The other stars are held fixed for didactic reasons) "Oggi" means today. "Anni" means years.
The discovery image of Alpha Centauri's candidate Neptunian planet, marked here as "C1".
Looking towards the sky around Orion from Alpha Centauri with Sirius near Betelgeuse, Procyon in Gemini, and the Sun in Cassiopeia generated by Celestia.
Simulated night-sky image with a "W" of stars from Cassiopeia connected by lines, and the Sun, labeled "Sol", as it would appear to the left of the "W"
The Very Large Telescope and Alpha Centauri

To the naked eye, the two main components appear to be a single star with an apparent magnitude of −0.27, the brightest star in the southern constellation of Centaurus and the third-brightest in the night sky, outshone only by Sirius and Canopus.

- Alpha Centauri

This proximity is the main reason for its brightness, as with other near stars such as Alpha Centauri, Procyon and Vega and in contrast to distant, highly luminous supergiants such as Canopus, Rigel or Betelgeuse.(Note that Canopus may be a bright giant) It is still around 25 times more luminous than the Sun.

- 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.

8 related topics with Alpha

Overall

Arcturus is the brightest star in the constellation of Boötes.

Arcturus

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Brightest star in the northern constellation of Boötes, the fourth-brightest in the night sky, and the brightest in the northern celestial hemisphere.

Brightest star in the northern constellation of Boötes, the fourth-brightest in the night sky, and the brightest in the northern celestial hemisphere.

Arcturus is the brightest star in the constellation of Boötes.
Optical image of Arcturus (DSS2 / MAST / STScI / NASA)
Arcturus in Arctophyllax
Arcturus next to the head of Comet Donati in 1858

With an apparent visual magnitude of −0.05, Arcturus is the brightest star in the northern celestial hemisphere and the fourth-brightest star in the night sky, after Sirius (−1.46 apparent magnitude), Canopus (−0.72) and α Centauri (combined magnitude of −0.27).

Relation between proper motion and velocity components of an object. A year ago the object was d units of distance from the Sun, and its light moved in a year by angle μ radian/s. If there has been no distortion by gravitational lensing or otherwise then μ = is the distance (usually expressed as annual velocity) transverse (tangential or perpendicular) to line of sight from the Sun. The angle is shaded light blue from the sun to the object's start point and its year later position as if it had no radial velocity. In this diagram the radial velocity happens to be one of the sun and object parting, so is positive.

Proper motion

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Astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more distant stars.

Astrometric measure of the observed changes in the apparent places of stars or other celestial objects in the sky, as seen from the center of mass of the Solar System, compared to the abstract background of the more distant stars.

Relation between proper motion and velocity components of an object. A year ago the object was d units of distance from the Sun, and its light moved in a year by angle μ radian/s. If there has been no distortion by gravitational lensing or otherwise then μ = is the distance (usually expressed as annual velocity) transverse (tangential or perpendicular) to line of sight from the Sun. The angle is shaded light blue from the sun to the object's start point and its year later position as if it had no radial velocity. In this diagram the radial velocity happens to be one of the sun and object parting, so is positive.
The celestial north and south poles are above/below CNP, CSP; the origin of all 24 hours of Right Ascension (the measure of absolute celestial east–west position), the March equinox (center of the sun's position then) at the J2000 epoch, is vector V. In red the diagram adds the components of proper motion across the celestial sphere. An ideal time to measure exactly such a small annual shift is at culmination. The culmination of the star is daily reached when the observer (and earth) passes as shown by the blue arrows "beneath" the star. The positive axes of the two components of its usually annually measured or published shift in proper motion are the exaggerated red arrows, note: the right arrows point to the east horizon. One red annotation is subtly shorter as the cosine of a star resting at 0° declination is 1, so such a star's east or west shift would not need to be multiplied by the cosine of its declination. The proper motion vector is μ, α = right ascension, δ = declination, θ = position angle (simply the 90° compliment of declination).
Barnard's Star, showing position every 5 years 1985–2005.
Proper motion of 61 Cygni in one year intervals.

After the Sun and the Alpha Centauri system, it is the nearest known star.

Proper motion was suspected by early astronomers (according to Macrobius, AD 400) but a proof was not provided until 1718 by Edmund Halley, who noticed that Sirius, Arcturus and Aldebaran were over half a degree away from the positions charted by the ancient Greek astronomer Hipparchus roughly 1850 years earlier.

Binary system of two stars

Binary star

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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).

Orbital periods can be less than an hour (for AM CVn stars), or a few days (components of Beta Lyrae), but also hundreds of thousands of years (Proxima Centauri around Alpha Centauri AB).

Animated 3D map of the nearest stars, centered on the Sun.

List of nearest stars and brown dwarfs

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This list covers all known stars, brown dwarfs, and sub-brown dwarfs within 20 ly of the Solar System.

This list covers all known stars, brown dwarfs, and sub-brown dwarfs within 20 ly of the Solar System.

Animated 3D map of the nearest stars, centered on the Sun.
Distance and angle conformal map of the celestial neighbourhood within 12 light years of Sol.
Distances of the nearest stars from 20,000 years ago until 80,000 years in the future

The Local Bubble also contains the neighboring G-Cloud, which contains the stars Alpha Centauri and Altair.

The brightest among these systems, as well as the brightest in Earth's night sky, is Sirius.

Just-saturated RGB-camera discs

Stellar classification

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Classification of stars based on their spectral characteristics.

Classification of stars based on their spectral characteristics.

Just-saturated RGB-camera discs
Main-sequence stars arranged from O to M Harvard classes
The Hertzsprung–Russell diagram relates stellar classification with absolute magnitude, luminosity, and surface temperature.
Montage of false color spectra for main-sequence stars
Guide for Secchi spectral types ("152 Schjellerup" is Y Canum Venaticorum)
Proper motion of stars of early type in ± 200,000 years
The movement of stars of late type around the apex (left) and antapex (right) in ± 200,000 years
The spectrum of an O5V star
B-class stars in the Jewel Box cluster (Credit: ESO VLT)
Class A Vega (left) compared to the Sun (right)
Canopus, an F-type supergiant and the second-brightest star in the night sky
The Sun, a G2 main-sequence star, with dark sunspots
Arcturus, a K1.5 giant compared to the Sun and Antares
UGC 5797, an emission-line galaxy where massive bright blue stars are formed
Hubble Space Telescope image of the nebula M1-67 and the Wolf–Rayet star WR 124 in the center
Artist's impression of an L-dwarf
Artist's impression of a T-dwarf
Artist's impression of a Y-dwarf
Image of the carbon star R Sculptoris and its striking spiral structure
Sirius A and B (a white dwarf of type DA2) resolved by Hubble

A1V – Sirius A

There are also giant K-type stars, which range from hypergiants like RW Cephei, to giants and supergiants, such as Arcturus, whereas orange dwarfs, like Alpha Centauri B, are main-sequence stars.

Some major asterisms, which feature many of the brightest stars in the night sky.

List of brightest stars

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List of stars arranged by their apparent magnitude – their brightness as observed from Earth.

List of stars arranged by their apparent magnitude – their brightness as observed from Earth.

Some major asterisms, which feature many of the brightest stars in the night sky.

The second brightest is Sirius at −1.46 mag.

Stellar brightness is traditionally based on the apparent visual magnitude as perceived by the human eye, from the brightest stars of 1st magnitude to the faintest at 6th magnitude. Since the invention of the optical telescope and the documenting of binary stars and multiple star systems, stellar brightness could be expressed as either individual (separate) or total (combined) magnitude. The table is ordered by combined magnitude of all naked eye components appearing as if it they were single stars. Such multiple star systems are indicated by parentheses showing the individual magnitudes of component stars bright enough to make a detectable contribution. For example, the binary star system Alpha Centauri has the total or combined magnitude of −0.27, while its two component stars have magnitudes of +0.01 and +1.33.

The constellation Carina with Canopus towards the right (west)

Canopus

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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.

English explorer Robert Hues brought Canopus to the attention of European observers in his 1592 work Tractatus de Globis, along with Achernar and Alpha Centauri, noting:"'Now, therefore, there are but three Stars of the first magnitude that I could perceive in all those parts which are never seene here in England. The first of these is that bright Star in the sterne of Argo which they call Canobus. The second is in the end of Eridanus. The third is in the right foote of the Centaure.'"

C. A. Jensen, Friedrich Wilhelm Bessel, 1839 (Ny Carlsberg Glyptotek)

Friedrich Bessel

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German astronomer, mathematician, physicist, and geodesist.

German astronomer, mathematician, physicist, and geodesist.

C. A. Jensen, Friedrich Wilhelm Bessel, 1839 (Ny Carlsberg Glyptotek)
Königsberg Observatory in 1830. It was destroyed by bombing in the Second World War.
Tabulae Regiomontanae reductionum observationum astronomicarum ab anno 1750 usque ad annum 1850 computatae, 1830

Nearly at the same time Friedrich Georg Wilhelm Struve and Thomas Henderson measured the parallaxes of Vega and Alpha Centauri.

As well as helping determine the parallax of 61 Cygni, Bessel's precise measurements using a new meridian circle from Adolf Repsold allowed him to notice deviations in the motions of Sirius and Procyon, which he deduced must be caused by the gravitational attraction of unseen companions.