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U Coronae Borealis, HD136175, HIP74881

U Coronae Borealis is a blue eclipsing main sequence dwarf star that can be located in the constellation of CoronaBorealis. U Coronae Borealis is the brightest star in Corona Borealis based on the Hipparcos 2007 apparent magnitude. The star can not be seen by the naked eye, you need a telescope to see it.

HIP74881 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD136175.

U Coronae Borealis has alternative name(s), U CrB.

Location of U Coronae Borealis

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 U Coronae Borealis, the location is 15h 18m 11.36 and +31d38`49.5 .

Proper Motion of U Coronae Borealis

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 -12.75 ± 0.40 miliarcseconds/year towards the north and -7.82 ± 0.59 miliarcseconds/year east if we saw them in the horizon.

U Coronae Borealis 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 140.0000000 that I have given is based on the Spectral Types page that I have found on the Internet. You might find a different figure, one that may have been calculated rather than generalised that I have done. The figure is always the amount times the luminosity of the Sun. It is an imprecise figure because of a number of factors including but not limited to whether the star is a variable star and distance.

Physical Properties (Colour, Temperature, Radius) of U Coronae Borealis

U Coronae Borealis has a spectral type of B7Vv SB. This means the star is a blue main sequence dwarf star. The star is 7321.00000000 Parsecs from the Galactic Centre or terms of Light Years is 23878.4184142400000000s. The star has a B-V Colour Index of -0.03 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 10,010 Kelvin.

U Coronae Borealis Radius has been calculated as being 2.86 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,988,464.80.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 2.11. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

U Coronae Borealis Apparent and Absolute Magnitudes

U Coronae Borealis has an apparent magnitude of 7.82 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 0.18 If you used the 2007 Parallax value, you would get an absolute magnitude of 0.84. 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 U Coronae Borealis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 2.96 which gave the calculated distance to U Coronae Borealis as 1101.90 light years away from Earth or 337.84 parsecs. It would take a spaceship travelling at the speed of light, 1101.90 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 4.02 which put U Coronae Borealis at a distance of 811.35 light years or 248.76 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 7,321.00 Parsecs or 23,878.42 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 U Coronae Borealis

The star is a eclipsing Beta Persei (Algol)/Semi-Detached System (subtype) 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. U Coronae Borealis brightness ranges from a magnitude of 8.900 to a magnitude of 7.813 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 3.5 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.

U Coronae Borealis Facts

Alternative Names

Traditional/Proper NameU Coronae Borealis
Short NameU CrB
Hipparcos Library I.D.74881
Bonner DurchmusterungBD+32 2569
Henry Draper Designation136175

Visual Facts

Star Typemain sequence dwarf star
Absolute Magnitude0.18 / 0.84
Visual / Apparent Magnitude7.82
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)15h 18m 11.36
Declination (Dec.)+31d38`49.5
Galactic Latitude57.87 degrees
Galactic Longitude49.95 degrees
1997 Distance from Earth2.96 Parallax (milliarcseconds)
 1101.90 Light Years
 337.84 Parsecs
2007 Revised Distance from Earth4.02 Parallax (milliarcseconds)
 811.35 Light Years
 248.76 Parsecs
Galacto-Centric Distance23,878.42 Light Years / 7,321.00 Parsecs
Proper Motion Dec.-12.75 ± 0.40 milliarcseconds/year
Proper Motion RA.-7.82 ± 0.59 milliarcseconds/year
B-V Index-0.03
Radial Velocity-8.50 ± 3.10 km/s
Spectral TypeB7Vv SB
Colour(B) blue

Variable Star Details

Variable Star ClassEclipsing
Variable Star TypeBeta Persei (Algol)/Semi-Detached System (subtype)
Mean Variability Period in Days3.453
Variable Magnitude Range (Brighter - Dimmer)7.813 - 8.900

Estimated Facts

Luminosity (x the Sun)140.0000000
Calculated Effective Temperature10,010 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars


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