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BU Circini

BU Circini Facts

BU Circini's Alternative Names

HIP72121 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD129557.

BU Circini has alternative name(s) :- BU Cir, BU Cir.

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

Location of BU Circini

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 BU Circini, the location is 14h 45m 10.97 and -55° 36` 05.8 .

Radial Velocity and Proper Motion of BU Circini

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 -8.75 ± 0.21 milliarcseconds/year towards the north and -6.47 ± 0.32 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 -6.40 km/s with an error of about 2.90 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.

BU Circini 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 555.94 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 BU Circini

BU Circini Colour and Temperature

BU Circini has a spectral type of B2III. This means the star is a blue giant star. The star has a B-V Colour Index of -0.06 which means the star's temperature is about 10,611 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu at being .

BU Circini Radius

Radius has been calculated as being 8.82 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 6,136,206.15.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 5.85. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures. The star's Iron Abundance is -0.12 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

BU Circini Apparent and Absolute Magnitudes

BU Circini has an apparent magnitude of 6.10 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 -2.52 If you used the 2007 Parallax value, you would get an absolute magnitude of -1.63. 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 BU Circini

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 1.89 which gave the calculated distance to BU Circini as 1725.73 light years away from Earth or 529.10 parsecs. If you want that in miles, it is 1,157,303,235,164.

In 2007, Hipparcos data was revised with a new parallax of 2.84 which put BU Circini at a distance of 1148.46 light years or 352.11 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 72,627,394.85 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 7,144.00 Parsecs or 23,301.11 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Travel Time to BU Circini

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)
Walking4192,544,093,435.34
Car1206,418,136,447.84
Airbus A3807361,046,435,290.41
Speed of Sound (Mach 1)767.2691,003,789,249.59
Concorde (Mach 2)1,534.54501,893,970.66
New Horizons Probe33,00023,338,677.99
Speed of Light670,616,629.001,148.46

Variable Type of BU Circini

The star is a pulsating Beta Cephei 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. BU Circini brightness ranges from a magnitude of 6.091 to a magnitude of 6.075 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.1 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 BU Circini Facts and Figures

Visual Facts


Primary / Proper / Traditional NameBU Circini
Alternative NamesBU Cir, HD 129557, HIP 72121, BU Cir
Spectral TypeB2III
Constellation's Main StarNo
Multiple Star SystemYes
Star TypeGiant Star
ColourBlue
GalaxyMilky Way
ConstellationCircinus
Absolute Magnitude -2.52 / -1.63
Visual / Apparent Magnitude6.10
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)14h 45m 10.97
Declination (Dec.)-55° 36` 05.8
Galactic Latitude3.78 degrees
Galactic Longitude318.57 degrees
1997 Distance from Earth1.89 Parallax (milliarcseconds)
 1725.73 Light Years
 529.10 Parsecs
2007 Distance from Earth2.84 Parallax (milliarcseconds)
 1148.46 Light Years
 352.11 Parsecs
 72,627,394.85 Astronomical Units
Galacto-Centric Distance23,301.11 Light Years / 7,144.00 Parsecs
Proper Motion Dec.-8.75 ± 0.21 milliarcseconds/year
Proper Motion RA.-6.47 ± 0.32 milliarcseconds/year
B-V Index-0.06
Radial Velocity-6.40 ± 2.90 km/s
Iron Abundance-0.12 ± 9.99 Fe/H
Eccentricity0.02
Semi-Major Axis7218.00
Stellar Luminosity (Lsun)555.94

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassPulsating
Variable Star TypeBeta Cephei
Mean Variability Period in Days0.128
Variable Magnitude Range (Brighter - Dimmer)6.075 - 6.091

Estimated Calculated Facts


Radius (x the Sun)5.85
Effective Temperature10,611 Kelvin

Sources and Links


SIMBAD SourceLink

Related Stars


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