Universe Guide

13 Sagittae - HD189577 - HIP98438

13 Sagittae is a red pulsating giant star that can be located in the constellation of Sagitta. HIP98438 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD189577. 13 Sagittae has alternative name(s), 13 Sagittae , VZ_Sge, 13 Sge.

Location of 13 Sagittae

The location of the star in the galaxy 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 13 Sagittae, the location is 20h 00m 03.31 and +17 d 30 ` 59.5 .

Proper Motion of 13 Sagittae

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 -012.00 ± 000.00 towards the north and 002.00 ± 000.00 east if we saw them in the horizon.

13 Sagittae 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 7.0000000 that I have given is based on the Spectral Types page that I have found on the Internet. You might find a different figure, one that may have been calculated rather than generalised that I have done. The figure is always the amount times the luminosity of the Sun. It is an imprecise figure because of a number of factors including but not limited to whether the star is a variable star and distance.

Physical Properties (Colour, Temperature, Radius) of 13 Sagittae

13 Sagittae has a spectral type of M4IIIa. This means the star is a red coloured giant star. The star has a B-V Colour Index of 1.57 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 3,850 Kelvin.

13 Sagittae has been calculated as 45.08 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 31,367,699.46.km.

13 Sagittae Apparent and Absolute Magnitudes

13 Sagittae has an apparent magnitude of 5.33 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 -1.66 If you used the 2007 Parallax value, you would get an absolute magnitude of -2.28. 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 13 Sagittae

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 4.00 which gave the calculated distance to 13 Sagittae as 815.41 light years away from Earth or 250 parsecs. In 2007, Hipparcos data was revised with a new parallax of 3.00 which put 13 Sagittae at a distance of 1087.21 light years or 333.33 parsecs.

It would take a spaceship travelling at the speed of light, 815.41 years using the 1997 distance to get there. We don't have the technology or spaceship that can carry people over that distance yet.

Variable Type of 13 Sagittae

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. 13 Sagittae brightness ranges from a magnitude of 5.000 to a magnitude of 5.000 over its variable period. The smaller the magnitude, the brighter the star.

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 Stellar Age, Metallicity or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

13 Sagittae Facts


Traditional Name13 Sagittae
Short NameVZ Sge, 13 Sge
Alternative Name(s)13 Sagittae
Hipparcos Library I.D.98438
Bonner DurchmusterungBD+17 4183
Henry Draper Designation189577
Celestial TypeStar
Absolute Magnitude-1.66 / -2.28
Apparent Magnitude5.33
Right Ascension (R.A.)20h 00m 03.31
Declination (Dec.)+17 d 30 ` 59.5
1997 Distance from Earth4.00 Parallax (milliarcseconds)
 815.41 Light Years
 250 Parsecs
2007 Distance from Earth3.00 Parallax (milliarcseconds)
 1087.21 Light Years
 333.33 Parsecs
Proper Motion Dec.-12.00 ± 0.00 milliarcseconds/year
Proper Motion RA.2.00 ± 0.00 milliarcseconds/year
B-V Index1.57
Spectral TypeM4IIIa
Colour(M) Red
Star Typegiant star
Variable Star ClassPulsating
Variable Star TypeSlow Irregular
Radius (x the Sun)45.08
Luminosity (x the Sun)7.0000000
Calculated Effective Temperature3,850 Kelvin


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