Universe Guide


BY Draconis, HD234677, HIP91009

BY Draconis is a orange to red rotating/eruptive main sequence dwarf star that can be located in the constellation of Draco. The star can not be seen by the naked eye, you need a telescope to see it.

HIP91009 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD234677. The Gliese ID of the star is Gliese GL719 AB. The star was part of the original catalogue devised by German Astronomer Wilheim Gliese of stars located within 20 parsecs of Earth. Ref : Star Names.

BY Draconis has alternative name(s), BY Dra.

Location of BY Draconis

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 BY Draconis, the location is 18h 33m 55.60 and +51d43`11.7 .

Proper Motion of BY Draconis

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 -324.69 ± 0.58 miliarcseconds/year towards the north and 186.51 ± 0.68 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of BY Draconis

BY Draconis has a spectral type of K7Vvar. This means the star is a orange to red main sequence dwarf star. The star is 7398.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24129.5641891200000000s. The star has a B-V Colour Index of 1.26 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 4,388 Kelvin.

BY Draconis Radius has been calculated as being 0.61 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 423,432.99.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 0.61. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

BY Draconis Apparent and Absolute Magnitudes

BY Draconis has an apparent magnitude of 8.20 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 7.12 If you used the 2007 Parallax value, you would get an absolute magnitude of 7.13. 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 BY Draconis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 60.90 which gave the calculated distance to BY Draconis as 53.56 light years away from Earth or 16.42 parsecs. It would take a spaceship travelling at the speed of light, 53.56 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 61.15 which put BY Draconis at a distance of 53.34 light years or 16.35 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.

The star's Galacto-Centric Distance is 7,398.00 Parsecs or 24,129.56 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 BY Draconis

The star is a rotating/eruptive BY Draconis and Eruptive UV Ceti 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. BY Draconis brightness ranges from a magnitude of 8.370 to a magnitude of 8.152 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.

BY Draconis Facts

Alternative Names

Traditional/Proper NameBY Draconis
Short NameBY Dra
Hipparcos Library I.D.91009
Bonner DurchmusterungBD+51 2402
Gliese ID719 AB
Henry Draper Designation234677

Visual Facts

Star Typemain sequence dwarf star
Absolute Magnitude7.12 / 7.13
Visual / Apparent Magnitude8.20
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)18h 33m 55.60
Declination (Dec.)+51d43`11.7
Galactic Latitude23.58 degrees
Galactic Longitude80.56 degrees
1997 Distance from Earth60.90 Parallax (milliarcseconds)
 53.56 Light Years
 16.42 Parsecs
2007 Revised Distance from Earth61.15 Parallax (milliarcseconds)
 53.34 Light Years
 16.35 Parsecs
Galacto-Centric Distance24,129.56 Light Years / 7,398.00 Parsecs
Proper Motion Dec.-324.69 ± 0.58 milliarcseconds/year
Proper Motion RA.186.51 ± 0.68 milliarcseconds/year
B-V Index1.26
Radial Velocity-25.43 ± 0.08 km/s
Semi-Major Axis3.11
Orbital Period (Days)114.02
Argument Of Periastron0.00
Spectral TypeK7Vvar
Colour(K) Orange to Red

Variable Star Details

Variable Star ClassRotating/Eruptive
Variable Star TypeBY Draconis and Eruptive UV Ceti
Mean Variability Period in Days0.176
Variable Magnitude Range (Brighter - Dimmer)8.152 - 8.370

Estimated Facts

Calculated Effective Temperature4,388 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

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