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Sephdar (Eta Sagittarii)

Sephdar Facts

Sephdar's Alternative Names

Eta Sagittarii (Eta Sgr) is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR6832. HIP89642 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD167618.

Sephdar has alternative name(s) :- Namalwarid, Rabah al Waridahm, Rabi al Waridah, Eta Sgr, eta 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 46 G. Sagittarii. There are no stars with a Gould designation in Ursa Major for example.

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

Location of Sephdar

The location of the giant 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 object is compared to the celestial equator and is expressed in degrees. For Sephdar, the location is 18h 17m 37.73 and -36° 45` 40.6 .

Radial Velocity and Proper Motion of Sephdar

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 -166.26 ± 0.16 miliarcseconds/year towards the north and -129.56 ± 0.24 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 0.20 km/s with an error of about 0.80 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.

Sephdar Luminosity

Luminosity is the amount of energy that a star pumps out and its relative to the amount that our star, the Sun gives out. The figure of 369.93 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Physical Properties (Colour, Temperature) of Sephdar

Sephdar has a spectral type of M2III. This means the star is a red giant star. The star is 7,356.00 Parsecs from the Galactic Centre or in terms of Light Years is 23,992.58 s. The star has a B-V Colour Index of 1.58 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 3,827 Kelvin.

Sephdar Radius has been calculated as being 23.29 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 16,205,889.35.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 22.76. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Sephdar Apparent and Absolute Magnitudes

Sephdar has an apparent magnitude of 3.10 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 -0.20 If you used the 2007 Parallax value, you would get an absolute magnitude of -0.15. 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 Sephdar

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 21.87 which gave the calculated distance to Sephdar as 149.14 light years away from Earth or 45.72 parsecs. It would take a spaceship travelling at the speed of light, 149.14 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 22.35 which put Sephdar at a distance of 145.93 light years or 44.74 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 9,228,223.13 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.

The star's Galacto-Centric Distance is 7,356.00 Parsecs or 23,992.58 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Variable Type of Sephdar

The star is a pulsating Slow Irregular 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. Sephdar brightness ranges from a magnitude of 3.171 to a magnitude of 3.125 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.0 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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Additional Sephdar Facts and Figures

Visual Facts


Primary / Proper / Traditional NameSephdar
Alternative NamesEta Sagittarii, Eta Sgr, Namalwarid, Rabah al Waridahm, Rabi al Waridah, Eta Sgr, HD 167618, HIP 89642, HR 6832, 46 G. Sagittarii, eta Sgr
Spectral TypeM2III
Constellation's Main StarNo
Multiple Star SystemYes
Star TypeGiant Star
ColourRed
GalaxyMilky Way
ConstellationSagittarius
Absolute Magnitude -0.20 / -0.15
Visual / Apparent Magnitude3.10
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)18h 17m 37.73
Declination (Dec.)-36° 45` 40.6
Galactic Latitude-9.68 degrees
Galactic Longitude356.43 degrees
1997 Distance from Earth21.87 Parallax (milliarcseconds)
 149.14 Light Years
 45.72 Parsecs
2007 Distance from Earth22.35 Parallax (milliarcseconds)
 145.93 Light Years
 44.74 Parsecs
 9,228,223.13 Astronomical Units
Galacto-Centric Distance23,992.58 Light Years / 7,356.00 Parsecs
Proper Motion Dec.-166.26 ± 0.16 milliarcseconds/year
Proper Motion RA.-129.56 ± 0.24 milliarcseconds/year
B-V Index1.58
Radial Velocity0.20 ± 0.80 km/s
Eccentricity0.27
Semi-Major Axis5636.00
Stellar Luminosity (Lsun)369.93

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassPulsating
Variable Star TypeSlow Irregular
Mean Variability Period in Days0.031
Variable Magnitude Range (Brighter - Dimmer)3.125 - 3.171

Estimated Calculated Facts


Radius (x the Sun)22.76
Effective Temperature3,827 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
167618-3612423.2A3.20000-128.00000-166.00000M4Red
B7.800001879
C13.000001896
D10.000001879

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