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21 G. Sagittarii, HD164402, HIP88298

21 G. Sagittarii is a blue supergiant star that can be located in the constellation of Sagittarius. The description is based on the spectral class. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

21 G. Sagittarii's Alternative Names

HIP88298 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD164402.

21 G. Sagittarii has alternative name(s) :- 21 G. Sgr.

The Gould star designation is one that was designed by American astronomer, Benjamin Apthorp Gould. Gould stars are predominantly in the Southern and Equatorial constellations but do appear in northern constellations such as Bootes and Orion. The star has the designation 21 G. Sagittarii. There are no stars with a Gould designation in Ursa Major for example.

BD number is the number that the star was filed under in the Durchmusterung or Bonner Durchmusterung, a star catalogue that was put together by the Bonn Observatory between 1859 to 1903. The star's BD Number is BD-22 4503.

More details on star alternative names can be found at Star Names .

Location of 21 G. Sagittarii

The location of the star in the night sky is determined by the Right Ascension (R.A.) and Declination (Dec.), these are equivalent to the Longitude and Latitude on the Earth. The Right Ascension is how far expressed in time (hh:mm:ss) the star is along the celestial equator. If the R.A. is positive then its eastwards. The Declination is how far north or south the star is compared to the celestial equator and is expressed in degrees. For 21 G. Sagittarii, the location is 18h 01m 54.38 and -22° 46` 49.0 .

Physical Properties (Colour, Temperature) of 21 G. Sagittarii

21 G. Sagittarii has a spectral type of B0Iab.... This means the star is a blue supergiant star. The star has a B-V Colour Index of -0.03 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 11,122 Kelvin.

21 G. Sagittarii Apparent and Absolute Magnitudes

21 G. Sagittarii has an apparent magnitude of 5.72 which is how bright we see the star from Earth. Apparent Magnitude is also known as Visual Magnitude. Using the supplied Parallax value, you would get an absolute magnitude of Magnitude, whether it be apparent/visual or absolute magnitude is measured by a number, the smaller the number, the brighter the Star is. Our own Sun is the brightest star and therefore has the lowest of all magnitudes, -26.74. A faint star will have a high number.

Distance to 21 G. Sagittarii

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as -0.14 which gave the calculated distance to 21 G. Sagittarii as -23297.38 light years away from Earth or -7142.86 parsecs. It would take a spaceship travelling at the speed of light, -23297.38 years to get there. We don't have the technology or spaceship that can carry people over that distance yet.

Source of Information

The source of the information if it has a Hip I.D. is from Simbad, the Hipparcos data library based at the University at Strasbourg, France. Hipparcos was a E.S.A. satellite operation launched in 1989 for four years. The items in red are values that I've calculated so they could well be wrong. Information regarding Metallicity and/or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

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21 G. Sagittarii Facts

Visual Facts


Primary / Proper / Traditional Name21 G. Sagittarii
Alternative Names21 G. Sgr, HD 164402, HIP 88298, BD-22 4503
Spectral TypeB0Iab...
Multiple Star SystemYes
Star Type very luminous Supergiant Star
Colour blue
GalaxyMilky Way
ConstellationSagittarius
Visual / Apparent Magnitude5.72
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)18h 01m 54.38
Declination (Dec.)-22° 46` 49.0
Galactic Latitude-0.03 degrees
Galactic Longitude7.16 degrees
Distance from Earth-0.14 Parallax (milliarcseconds)
 -23297.38 Light Years
 -7142.86 Parsecs
B-V Index-0.03
Radial Velocity4.20 ± 1.40 km/s

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Facts


Calculated Effective Temperature11,122 Kelvin

Sources and Links


SIMBAD SourceLink

Multi-Star System

The star has been identified as being a multi-star system, one in which there is at least one star in close orbit to another star or two or more stars orbiting a central point. The stars may be of equal mass, unequal mass where one star is stronger than the other or be in groups orbiting a central point which doesn't necessarily have to be a star. More information can be found on my dedicated multiple star systems page. The source of the info is Simbad. The file is dated 2000 so any differences between this and any other source will be down to the actual source from where the information came from.


Proper Motion mas/yr
H.D. IdB.D. IdStar CodeMagnitudeR.A.Dec.SpectrumColourYear
164402-22 4503.0A5.70000-1.00000-9.00000B0Blue/White
B12.800001878
C14.000001892

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