Universe Guide

13 Sagittae

13 Sagittae Facts

13 Sagittae's Alternative Names

The Id of the star in the Yale Bright Star Catalogue is HR7645. 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) :- , VZ Sge.

Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John numbered the stars in the constellation with a number and the latin name, this star's Flamsteed designation is 13 Sagittae with it shortened to 13 Sge.

BD number is the number that the star was filed under in the Durchmusterung or Bonner Durchmusterung, a star catalogue that was put together by the Bonn Observatory between 1859 to 1903. The star's BD Number is BD+17 4183.

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

Location of 13 Sagittae

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 13 Sagittae, the location is 20h 00m 03.31 and +17° 30` 59.5 .

Radial Velocity and Proper Motion of 13 Sagittae

Proper Motion

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 -12.41 ± 0.20 milliarcseconds/year towards the north and 1.75 ± 0.31 milliarcseconds/year east if we saw them in the horizon.

Radial Velocity

The Radial Velocity, that is the speed at which the star is moving away/towards the Sun is -17.56 km/s with an error of about 0.33 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.

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 2,173.57 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 13 Sagittae

13 Sagittae Colour and Temperature

13 Sagittae has a spectral type of M4IIIa. This means the star is a red 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 Radius

Radius has been calculated as being 41.30 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 28,739,605.54.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 56.23. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

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 -1.47 If you used the 2007 Parallax value, you would get an absolute magnitude of -2.14. 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 4.37 which gave the calculated distance to 13 Sagittae as 746.37 light years away from Earth or 228.83 parsecs. It would take a spaceship travelling at the speed of light, 746.37 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 3.20 which put 13 Sagittae at a distance of 1019.26 light years or 312.5 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 64,457,302.81 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 7,235.00 Parsecs or 23,597.92 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 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 5.462 to a magnitude of 5.253 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.2 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 13 Sagittae Facts and Figures

Visual Facts

Primary / Proper / Traditional Name13 Sagittae
Alternative NamesHD 189577, HIP 98438, HR 7645, 13 Sge, BD+17 4183, VZ Sge
Spectral TypeM4IIIa
Constellation's Main StarNo
Multiple Star SystemYes
Star TypeGiant Star
GalaxyMilky Way
Absolute Magnitude -1.47 / -2.14
Visual / Apparent Magnitude5.33
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)20h 00m 03.31
Declination (Dec.)+17° 30` 59.5
Galactic Latitude-6.49 degrees
Galactic Longitude56.43 degrees
1997 Distance from Earth4.37 Parallax (milliarcseconds)
 746.37 Light Years
 228.83 Parsecs
2007 Distance from Earth3.20 Parallax (milliarcseconds)
 1019.26 Light Years
 312.5 Parsecs
 64,457,302.81 Astronomical Units
Galacto-Centric Distance23,597.92 Light Years / 7,235.00 Parsecs
Proper Motion Dec.-12.41 ± 0.20 milliarcseconds/year
Proper Motion RA.1.75 ± 0.31 milliarcseconds/year
B-V Index1.57
Radial Velocity-17.56 ± 0.33 km/s
Semi-Major Axis6598.00
Stellar Luminosity (Lsun)2,173.57

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeSlow Irregular
Mean Variability Period in Days0.199
Variable Magnitude Range (Brighter - Dimmer)5.253 - 5.462

Estimated Calculated Facts

Radius (x the Sun)56.23
Effective Temperature3,850 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
189577+17 4183.0A5.6000015.00000-14.00000M2Red
+17 4186.0D10.30000-13.00000-16.00000KOrange1904
+17 4184.0DE10.30000-4.0000015.000001904

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