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BU Circini, HD129557, HIP72121

BU Circini is a blue pulsating giant star that can be located in the constellation of Circinus. BU Circini is the brightest star in Circinus based on the Hipparcos 2007 apparent magnitude. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

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.

Location of BU Circini

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

Proper Motion of BU Circini

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 miliarcseconds/year towards the north and -6.47 ± 0.32 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of BU Circini

BU Circini has a spectral type of B2III. This means the star is a blue giant star. The star is 7144.00000000 Parsecs from the Galactic Centre or terms of Light Years is 23301.1092953600000000s. The star has a B-V Colour Index of -0.06 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 10,611 Kelvin.

BU Circini 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. 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. It would take a spaceship travelling at the speed of light, 1725.73 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 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.

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*.

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.

BU Circini Facts

Alternative Names

Traditional/Proper NameBU Circini
Short NameBU Cir
Hipparcos Library I.D.72121
Henry Draper Designation129557

Visual Facts

Star Typegiant star
Absolute Magnitude-2.52 / -1.63
Visual / Apparent Magnitude6.10
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)14h 45m 10.97
Declination (Dec.)-55d 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 Revised Distance from Earth2.84 Parallax (milliarcseconds)
 1148.46 Light Years
 352.11 Parsecs
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
Spectral TypeB2III
Colour(B) blue

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 Facts

Calculated Effective Temperature10,611 Kelvin

Sources and Links

SIMBAD SourceLink

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