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W Sagittarii, HD164975, HIP88567, HR6742

W Sagittarii is a white to yellow pulsating luminous giant star that can be located in the constellation of Sagittarius. The description is based on the spectral class. W Sagittarii is not part of the constellation but is within the borders of the constellation.

The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

W Sagittarii's Alternative Names

The Id of the star in the Yale Bright Star Catalogue is HR6742. HIP88567 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD164975.

W Sagittarii has alternative name(s) :- , W 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 26 G. Sagittarii. There are no stars with a Gould designation in Ursa Major for example.

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

Location of W 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 W Sagittarii, the location is 18h 05m 01.22 and -29° 34` 48.3 .

Radial Velocity and Proper Motion of W Sagittarii

All stars like planets orbit round a central spot, in the case of planets, its the central star such as the Sun. In the case of a star, its the galactic centre. The constellations that we see today will be different than they were 50,000 years ago or 50,000 years from now. Proper Motion details the movements of these stars and are measured in milliarcseconds. The star is moving -5.28 ± 0.62 miliarcseconds/year towards the north and 2.62 ± 1.12 miliarcseconds/year east if we saw them in the horizon.

The Radial Velocity, that is the speed at which the star is moving away/towards the Sun is -28.04 km/s with an error of about 0.07 km/s . When the value is negative then the star and the Sun are getting closer to one another, likewise, a positive number means that two stars are moving away. Its nothing to fear as the stars are so far apart, they won't collide in our life-time, if ever.

Physical Properties (Colour, Temperature) of W Sagittarii

W Sagittarii has a spectral type of G0Ib/II. This means the star is a white to yellow luminous giant star. The star has a B-V Colour Index of 0.77 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 5,490 Kelvin.

W Sagittarii Radius has been calculated as being 76.88 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 53,491,644.02.km. If you need the diameter of the star, you just need to multiple the radius by 2. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 32.19. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures. The star's Iron Abundance is 0.28 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

W Sagittarii Apparent and Absolute Magnitudes

W Sagittarii has an apparent magnitude of 4.66 which is how bright we see the star from Earth. Apparent Magnitude is also known as Visual Magnitude. If you used the 1997 Parallax value, you would get an absolute magnitude of -4.36 If you used the 2007 Parallax value, you would get an absolute magnitude of -2.47. 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 W Sagittarii

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 1.57 which gave the calculated distance to W Sagittarii as 2077.47 light years away from Earth or 636.94 parsecs. It would take a spaceship travelling at the speed of light, 2077.47 years to get there. We don't have the technology or spaceship that can carry people over that distance yet.

In 2007, Hipparcos data was revised with a new parallax of 3.75 which put W Sagittarii at a distance of 869.77 light years or 266.67 parsecs. It should not be taken as though the star is moving closer or further away from us. It is purely that the distance was recalculated.

Using the 2007 distance, the star is roughly 55,004,252.61 Astronomical Units from the Earth/Sun give or take a few. An Astronomical Unit is the distance between Earth and the Sun. The number of A.U. is the number of times that the star is from the Earth compared to the Sun.

Variable Type of W Sagittarii

The star is a pulsating Delta Cepheid variable type which means that its size changes over time. The Variable Type is usually named after the first star of that type to be spotted. W Sagittarii brightness ranges from a magnitude of 5.243 to a magnitude of 4.393 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 7.6 days (variability).

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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W Sagittarii Facts

Visual Facts


Primary / Proper / Traditional NameW Sagittarii
Alternative NamesW Sgr, HD 164975, HIP 88567, HR 6742, 26 G. Sagittarii, W Sgr
Spectral TypeG0Ib/II
Constellation's Main StarNo
Multiple Star SystemYes
Star TypeLuminous Giant Star
Colour white to yellow
GalaxyMilky Way
ConstellationSagittarius
Absolute Magnitude -4.36 / -2.47
Visual / Apparent Magnitude4.66
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)18h 05m 01.22
Declination (Dec.)-29° 34` 48.3
Galactic Latitude-3.98 degrees
Galactic Longitude1.58 degrees
1997 Distance from Earth1.57 Parallax (milliarcseconds)
 2077.47 Light Years
 636.94 Parsecs
2007 Distance from Earth3.75 Parallax (milliarcseconds)
 869.77 Light Years
 266.67 Parsecs
 55,004,252.61 Astronomical Units
Proper Motion Dec.-5.28 ± 0.62 milliarcseconds/year
Proper Motion RA.2.62 ± 1.12 milliarcseconds/year
B-V Index0.77
Radial Velocity-28.04 ± 0.07 km/s
Iron Abundance0.28 ± 9.99 Fe/H
Associated / Clustered StarsAlnasl

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassPulsating
Variable Star TypeDelta Cepheid
Mean Variability Period in Days7.594
Variable Magnitude Range (Brighter - Dimmer)4.393 - 5.243

Estimated Facts


Calculated Effective Temperature5,490 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
164975-2914447.2A13.00000-2.00000F8Yellow/White
B13.500001897
C13.500001897

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