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FG Sagittae, HIP99527

Primary Facts on FG Sagittae

  • FG Sagittae's star type is pulsating supergiant star that can be located in the constellation of Sagitta. The description is based on the spectral class.
  • FG Sagittae is not part of the constellation outline but is within the borders of the constellation.
  • Based on the spectral type (B4Ieq-K2Ib) of the star, the star's colour is blue .
  • The star can not be seen by the naked eye, you need a telescope to see it.
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 606.25 light years away from us.

FG Sagittae's Alternative Names

HIP99527 is the reference name for the star in the Hipparcos Star Catalogue.

FG Sagittae has alternative name(s) :- , FG Sge.

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

Location of FG Sagittae

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 FG Sagittae, the location is 20h 11m 56.06 and +20° 20` 04.4 .

Radial Velocity and Proper Motion of FG 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 -8.60 ± 1.21 miliarcseconds/year towards the north and 0.44 ± 1.77 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 37.50 km/s with an error of about 0.60 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 FG Sagittae

FG Sagittae has a spectral type of B4Ieq-K2Ib. This means the star is a blue supergiant star. The star has a B-V Colour Index of 1.91 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 2,411 Kelvin.

FG Sagittae Radius has been calculated as being 16.54 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 11,507,165.91.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 14.14. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

FG Sagittae Apparent and Absolute Magnitudes

FG Sagittae has an apparent magnitude of 9.24 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 2.55 If you used the 2007 Parallax value, you would get an absolute magnitude of 2.89. 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 FG Sagittae

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 4.60 which gave the calculated distance to FG Sagittae as 709.05 light years away from Earth or 217.39 parsecs. It would take a spaceship travelling at the speed of light, 709.05 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 5.38 which put FG Sagittae at a distance of 606.25 light years or 185.87 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 38,338,172.39 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 FG 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. FG Sagittae brightness ranges from a magnitude of 9.731 to a magnitude of 9.165 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.5 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 FG Sagittae Facts and Figures

Visual Facts


Primary / Proper / Traditional NameFG Sagittae
Alternative NamesHIP 99527, FG Sge
Spectral TypeB4Ieq-K2Ib
Constellation's Main StarNo
Multiple Star SystemYes
Star Type very luminous Supergiant Star
Colour blue
GalaxyMilky Way
ConstellationSagitta
Absolute Magnitude 2.55 / 2.89
Visual / Apparent Magnitude9.24
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)20h 11m 56.06
Declination (Dec.)+20° 20` 04.4
Galactic Latitude-7.39 degrees
Galactic Longitude60.33 degrees
1997 Distance from Earth4.60 Parallax (milliarcseconds)
 709.05 Light Years
 217.39 Parsecs
2007 Distance from Earth5.38 Parallax (milliarcseconds)
 606.25 Light Years
 185.87 Parsecs
 38,338,172.39 Astronomical Units
Proper Motion Dec.-8.60 ± 1.21 milliarcseconds/year
Proper Motion RA.0.44 ± 1.77 milliarcseconds/year
B-V Index1.91
Radial Velocity37.50 ± 0.60 km/s

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassPulsating
Variable Star TypeSlow Irregular
Mean Variability Period in Days0.528
Variable Magnitude Range (Brighter - Dimmer)9.165 - 9.731

Estimated Facts


Calculated Effective Temperature2,411 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
A8.20000B4Blue/White
B1972

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