A report on Binary star and Double star

Binary system of two stars
Astronomers have mistakenly reported observations of a double star in place of J 900 and a faint star in the constellation of Gemini.
Edge-on disc of gas and dust present around the binary star system HD 106906
Artist's impression of the discs around the young stars HK Tauri A and B.
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)

This occurs because the pair either forms a binary star (i.e. a binary system of stars in mutual orbit, gravitationally bound to each other) or is an optical double, a chance line-of-sight alignment of two stars at different distances from the observer.

- Double star

The more general term double star is used for pairs of stars which are seen to be close together in the sky.

- Binary star
Binary system of two stars

6 related topics with Alpha

Overall

Star system named DI Cha. While only two stars are apparent, it is actually a quadruple system containing two sets of binary stars.

Star system

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Small number of stars that orbit each other, bound by gravitational attraction.

Small number of stars that orbit each other, bound by gravitational attraction.

Star system named DI Cha. While only two stars are apparent, it is actually a quadruple system containing two sets of binary stars.
Orbits of the HR 6819 hierarchical triple star system: an inner binary with one star (orbit in blue) and a black hole (orbit in red), encircled by another star in a wider orbit (also in blue).
Subsystem notation in Tokovinin's Multiple Star Catalogue
Sirius A (center), with its white dwarf companion, Sirius B (lower left) taken by the Hubble Space Telescope.
HD 98800 is a quadruple star system located in the TW Hydrae association.

A star system of two stars is known as a binary star, binary star system or physical double star.

The Big Dipper's bowl and part of the handle photographed from the International Space Station. Mizar and Alcor are at the upper right.

Mizar

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Second-magnitude star in the handle of the Big Dipper asterism in the constellation of Ursa Major.

Second-magnitude star in the handle of the Big Dipper asterism in the constellation of Ursa Major.

The Big Dipper's bowl and part of the handle photographed from the International Space Station. Mizar and Alcor are at the upper right.
The multiple star system of Mizar (the double star on the right) and Alcor (left). The unrelated, fainter star Sidus Ludovicianum can be seen lower down.
Radial velocity curves for the two almost identical components

It forms a well-known naked eye double star with the fainter star Alcor, and is itself a quadruple star system.

Mizar is a visual double with a separation of 14.4 arcseconds, each of which is a spectroscopic binary.

A visual band light curve for YY Geminorum (Castor C), adapted from Butler et al. (2015)

Castor (star)

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Second-brightest object in the zodiac constellation of Gemini.

Second-brightest object in the zodiac constellation of Gemini.

A visual band light curve for YY Geminorum (Castor C), adapted from Butler et al. (2015)

Castor appears singular to the naked eye, but it is actually a sextuple star system organized into three binary pairs.

Appearing to the naked eye as a single star, Castor was first recorded as a double star in 1718 by James Pound, but it may have been resolved into at least two sources of light by Cassini as early as 1678.

Mizar and Alcor in constellation Ursa Major

Mizar and Alcor

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Mizar and Alcor in constellation Ursa Major

Mizar and Alcor are two stars forming a naked eye double in the handle of the Big Dipper (or Plough) asterism in the constellation of Ursa Major.

Mizar, also designated Zeta Ursae Majoris (ζ Ursae Majoris, abbreviated Zeta UMa, ζ UMa), is itself a quadruple system and Alcor, also designated 80 Ursae Majoris (80 UMa), is a binary, the pair together forming a sextuple system.

Alpha Centauri is the brightest object in the constellation of Centaurus (top left).

Alpha Centauri

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Gravitationally bound system of the closest stars and planets to the Solar System at 4.37 light-years from the Sun.

Gravitationally bound system of the closest stars and planets to the Solar System at 4.37 light-years from the Sun.

Alpha Centauri is the brightest object in the constellation of Centaurus (top left).
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 relative sizes and colours of stars in the Alpha Centauri system, compared to the Sun
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.
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.
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.
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.
Closest stars to the Sun
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

Alpha Centauri A and B are Sun-like stars (Class G and K, respectively), and together they form the binary star Alpha Centauri AB.

For example, in about 6,200 AD, α Centauri's true motion will cause an extremely rare first-magnitude stellar conjunction with Beta Centauri, forming a brilliant optical double star in the southern sky.

Detail of Bayer's chart for Orion showing the belt stars and Orion Nebula region, with both Greek and Latin letter labels visible

Bayer designation

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Stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name.

Stellar designation in which a specific star is identified by a Greek or Latin letter followed by the genitive form of its parent constellation's Latin name.

Detail of Bayer's chart for Orion showing the belt stars and Orion Nebula region, with both Greek and Latin letter labels visible
Orion constellation map

Usually these are double stars (mostly optical doubles rather than true binary stars), but there are some exceptions such as the chain of stars π1, π2, π3, π4, π5 and π6 Orionis.