A report on Double star and Mizar and Alcor

Astronomers have mistakenly reported observations of a double star in place of J 900 and a faint star in the constellation of Gemini.
Mizar and Alcor in constellation Ursa Major
Artist's impression of the discs around the young stars HK Tauri A and B.

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 and Alcor

The only (possible) case of "binary star" whose two components are separately visible to the naked eye is the case of Mizar and Alcor (though actually a multiple-star system), but it is not known for sure whether Mizar and Alcor are gravitationally bound.

- Double star
Astronomers have mistakenly reported observations of a double star in place of J 900 and a faint star in the constellation of Gemini.

2 related topics with Alpha

Overall

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.

The Mizar and Alcor system lies about 83 light-years away from the Sun, as measured by the Hipparcos astrometry satellite, and is part of the Ursa Major Moving Group.

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)

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

The Alcor–Mizar visual binary in Ursa Majoris also consists of six stars: four comprising Mizar and two comprising Alcor.