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BK Hydrae

BK Hydrae Facts

  • BK Hydrae is a pulsating variable star that can be located in the constellation of Hydra. The description is based on the spectral class.
  • BK Hydrae is not part of the constellation outline but is within the borders of the constellation.
  • Based on the spectral type (K5) of the star, the star's colour is orange to red .
  • 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 1606.72 light years away from us. Distance

BK Hydrae's Alternative Names

HIP55347 is the reference name for the star in the Hipparcos Star Catalogue.

BK Hydrae has alternative name(s) :- , BK Hya.

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

Location of BK Hydrae

The location of the variable 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 BK Hydrae, the location is 11h 20m 03.12 and -35° 15` 23.8 .

Proper Motion of BK Hydrae

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 -6.70 ± 0.80 milliarcseconds/year towards the north and 7.43 ± 1.07 milliarcseconds/year east if we saw them in the horizon. . 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 of BK Hydrae

BK Hydrae Colour and Temperature

Based on the star's spectral type of K5 , BK Hydrae's colour and type is orange to red variable star. The star has a B-V Colour Index of 1.82 which means the star's temperature is about 2,923 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu.

BK Hydrae Radius

BK Hydrae estimated radius has been calculated as being 19.92 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 13,858,535.50.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 33.670076731506204988595699314. The figure is derived at by using the formula from SDSS rather than peer reviewed papers. It has been known to produce widely incorrect figures.

BK Hydrae Apparent and Absolute Magnitudes

BK Hydrae has an apparent magnitude of 8.63 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 1.31 If you used the 2007 Parallax value, you would get an absolute magnitude of 0.17. 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 BK Hydrae

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 3.43000 which gave the calculated distance to BK Hydrae as 950.91 light years away from Earth or 291.55 parsecs. If you want that in miles, it is about 5,590,043,653,614,026.59, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 2.03000 which put BK Hydrae at a distance of 1606.72 light years or 492.61 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 101,607,398.20 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.

Travel Time to BK Hydrae

The time it will take to travel to this star is dependent on how fast you are going. U.G. has done some calculations as to how long it will take going at differing speeds. A note about the calculations, when I'm talking about years, I'm talking non-leap years only (365 days).

The New Horizons space probe is the fastest probe that we've sent into space at the time of writing. Its primary mission was to visit Pluto which at the time of launch (2006), Pluto was still a planet.

DescriptionSpeed (m.p.h.)Time (years)
Walking4269,373,287,536.72
Car1208,979,109,584.56
Airbus A3807361,463,985,258.35
Speed of Sound (Mach 1)767.2691,404,322,538.96
Concorde (Mach 2)1,534.54702,160,354.34
New Horizons Probe33,00032,651,307.58
Speed of Light670,616,629.001,606.72

Variable Type of BK Hydrae

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. BK Hydrae brightness ranges from a magnitude of 9.025 to a magnitude of 8.448 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.6 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 BK Hydrae Facts and Figures

Visual Facts


Primary / Proper / Traditional NameBK Hydrae
Alternative NamesHIP 55347, BK Hya
Spectral TypeK5
Constellation's Main StarNo
Multiple Star SystemNo / Unknown
Star TypeVariable Star
ColourOrange to Red
GalaxyMilky Way
ConstellationHydra
Absolute Magnitude 1.31 / 0.17
Visual / Apparent Magnitude8.63
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)11h 20m 03.12
Declination (Dec.)-35° 15` 23.8
Galactic Latitude23.98616782 degrees
Galactic Longitude282.62719692 degrees
1997 Distance from Earth3.43000 Parallax (milliarcseconds)
 950.91 Light Years
 291.55 Parsecs
2007 Distance from Earth2.03000 Parallax (milliarcseconds)
 1606.72 Light Years
 492.61 Parsecs
 101,607,398.20 Astronomical Units
Proper Motion Dec.-6.70000 ± 0.80000 milliarcseconds/year
Proper Motion RA.7.43000 ± 1.07000 milliarcseconds/year
B-V Index1.82

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassPulsating
Variable Star TypeSlow Irregular
Mean Variability Period in Days0.575
Variable Magnitude Range (Brighter - Dimmer)8.448 - 9.025

Estimated Calculated Facts


Radius (x the Sun)33.67
Effective Temperature2,923 Kelvin

Sources and Links


SIMBAD SourceLink

Related Stars


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