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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 description is based on the spectral class. BY Draconis is not part of the constellation but is within the borders of the constellation.

The star can not be seen by the naked eye, you need a telescope to see it.

BY Draconis's Alternative Names

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 GL 719AB. The star was part of the original catalogue devised by German Astronomer Wilheim Gliese of stars located within 20 parsecs of Earth. Star Names

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

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+51 2402.

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

Location of BY Draconis

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 BY Draconis, the location is 18h 33m 55.60 and +51° 43` 11.7 .

Radial Velocity and 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.

The Radial Velocity, that is the speed at which the star is moving away/towards the Sun is -25.43 km/s with an error of about 0.08 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.

BY Draconis 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 0.23 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 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 7,398.00 Parsecs from the Galactic Centre or terms of Light Years is 24,129.56 s. 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. 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 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.

Using the 2007 distance, the star is roughly 3,372,406.08 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 7,398.00 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 Erup 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.

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BY Draconis Facts

Visual Facts


Primary / Proper / Traditional NameBY Draconis
Alternative NamesHD 234677, HIP 91009, BD+51 2402, Gliese 719AB, BY Dra
Spectral TypeK7Vvar
Constellation's Main StarNo
Multiple Star SystemYes
Star Type main sequence Dwarf Star
Colour orange to red
GalaxyMilky Way
ConstellationDraco
Absolute Magnitude 7.12 / 7.13
Visual / Apparent Magnitude8.20
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)18h 33m 55.60
Declination (Dec.)+51° 43` 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 Distance from Earth61.15 Parallax (milliarcseconds)
 53.34 Light Years
 16.35 Parsecs
 3,372,406.08 Astronomical Units
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 Index 1.26
Radial Velocity-25.43 ± 0.08 km/s
Eccentricity0.15
Inclination113.21
Semi-Major Axis7299.00
Stellar Luminosity (Lsun)0.23
Orbital Period (Days)114.02
Argument Of Periastron0.00

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassRotating/Eruptive
Variable Star TypeBY Draconis and Erup
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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