A report on Bayer designation and Double star

Detail of Bayer's chart for Orion showing the belt stars and Orion Nebula region, with both Greek and Latin letter labels visible
Astronomers have mistakenly reported observations of a double star in place of J 900 and a faint star in the constellation of Gemini.
Orion constellation map
Artist's impression of the discs around the young stars HK Tauri A and B.

Some bright visual double stars have a Bayer designation.

- Double star

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.

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

3 related topics with Alpha

Overall

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.

In cases where the binary star has a Bayer designation and is widely separated, it is possible that the members of the pair will be designated with superscripts; an example is Zeta Reticuli, whose components are ζ1 Reticuli and ζ2 Reticuli.

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)

It has the Bayer designation α Geminorum, which is Latinised to Alpha Geminorum and abbreviated Alpha Gem or α Gem.

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.

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.

Two or more stars, double stars or open star clusters, which are moving in similar directions, exhibit so-called shared or common proper motion (or cpm.), suggesting they may be gravitationally attached or share similar motion in space.

In 1992 Rho Aquilae became the first star to have its Bayer designation invalidated by moving to a neighbouring constellation – it is now in Delphinus.