Universe Guide


Theta Sagittae - HD191570 - HIP99352

Theta Sagittae is a blue to white subgiant star that can be located in the constellation of Sagitta. Theta Sagittae is the Bayer Classification for the star. HIP99352 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD191570. Theta Sagittae has alternative name(s), 17 Sagittae , 17 Sge. Theta Sagittae is a multiple star system with 2 stars orbiting in its solar system.

Location of Theta 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 Theta Sagittae, the location is 20h 09m 56.61 and +20d54`53.2 .

Proper Motion of Theta 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 98.43 ± 0.58 miliarcseconds/year towards the north and 59.68 ± 0.89 miliarcseconds/year east if we saw them in the horizon.

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

Theta Sagittae has a spectral type of F5IV. This means the star is a blue to white subgiant star. The star has a B-V Colour Index of 0.39 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 6,775 Kelvin.

Theta Sagittae has been calculated as 1.52 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,060,565.32.km.

Theta Sagittae Apparent and Absolute Magnitudes

Theta Sagittae has an apparent magnitude of 6.51 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 3.24 If you used the 2007 Parallax value, you would get an absolute magnitude of 3.23. 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 Theta Sagittae

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 22.22 which gave the calculated distance to Theta Sagittae as 146.79 light years away from Earth or 45.00 parsecs. It would take a spaceship travelling at the speed of light, 146.79 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 22.10 which put Theta Sagittae at a distance of 147.59 light years or 45.25 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.

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.

Theta Sagittae Facts

Alternative Names

Short Name17 Sge
Bayer DesignationTheta Sagittae
Alternative Name(s)17 Sagittae
Hipparcos Library I.D.99352
Bonner DurchmusterungBD+20 4453
Henry Draper Designation191570

Visual Facts

Star Typesubgiant star
Absolute Magnitude3.24 / 3.23
Apparent Magnitude6.51
Right Ascension (R.A.)20h 09m 56.61
Declination (Dec.)+20d54`53.2
1997 Distance from Earth22.22 Parallax (milliarcseconds)
 146.79 Light Years
 45.00 Parsecs
2007 Revised Distance from Earth22.10 Parallax (milliarcseconds)
 147.59 Light Years
 45.25 Parsecs
Proper Motion Dec.98.43 ± 0.58 milliarcseconds/year
Proper Motion RA.59.68 ± 0.89 milliarcseconds/year
B-V Index0.39
Spectral TypeF5IV
Colour(F) blue to white
Stars in Solar System2

Estimated Facts

Radius (x the Sun)1.52
Calculated Effective Temperature6,775 Kelvin

Sources and Links

SIMBAD SourceLink

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