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BL Crucis - HD108396 - HIP60781

BL Crucis is a red pulsating giant star that can be located in the constellation of Crux. BL Crucis is the brightest star in Crux 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.

HIP60781 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD108396.

BL Crucis has alternative name(s), BL_Cru.

Location of BL Crucis

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 BL Crucis, the location is 12h 27m 28.88 and -58d59`30.4 .

Proper Motion of BL Crucis

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 5.92 ± 0.22 miliarcseconds/year towards the north and -13.82 ± 0.32 miliarcseconds/year east if we saw them in the horizon.

BL Crucis 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 7.0000000 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 BL Crucis

BL Crucis has a spectral type of M4/M5III. This means the star is a red giant star. The star is 7334.00000000 Parsecs from the Galactic Centre or terms of Light Years is 23920.8196489600000000s. The star has a B-V Colour Index of 1.54 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 3,913 Kelvin.

BL Crucis Radius has been calculated as being 29.64 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 20,624,155.99.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 23.22. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

BL Crucis Apparent and Absolute Magnitudes

BL Crucis has an apparent magnitude of 5.38 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 -0.82 If you used the 2007 Parallax value, you would get an absolute magnitude of -0.29. 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 BL Crucis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 5.76 which gave the calculated distance to BL Crucis as 566.26 light years away from Earth or 173.61 parsecs. It would take a spaceship travelling at the speed of light, 566.26 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 7.36 which put BL Crucis at a distance of 443.16 light years or 135.87 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 7,334.00 Parsecs or 23,920.82 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 BL Crucis

The star is a pulsating Semi-Regular Star which are giants or supergiants of intermediate and late spectral 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. BL Crucis brightness ranges from a magnitude of 6.000 to a magnitude of 5.000 over its variable period. The smaller the magnitude, the brighter the star.

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.

BL Crucis Facts

Alternative Names

Traditional/Proper NameBL Crucis
Short NameBL Cru
Hipparcos Library I.D.60781
Henry Draper Designation108396

Visual Facts

Star Typegiant star
Absolute Magnitude-0.82 / -0.29
Visual / Apparent Magnitude5.38
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)12h 27m 28.88
Declination (Dec.)-58d59`30.4
Galactic Latitude3.74 degrees
Galactic Longitude299.84 degrees
1997 Distance from Earth5.76 Parallax (milliarcseconds)
 566.26 Light Years
 173.61 Parsecs
2007 Revised Distance from Earth7.36 Parallax (milliarcseconds)
 443.16 Light Years
 135.87 Parsecs
Galacto-Centric Distance23,920.82 Light Years / 7,334.00 Parsecs
Proper Motion Dec.5.92 ± 0.22 milliarcseconds/year
Proper Motion RA.-13.82 ± 0.32 milliarcseconds/year
B-V Index1.54
Radial Velocity76.20 ± 1.30 km/s
Spectral TypeM4/M5III
Colour(M) Red

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeSemi-Regular Star which are giants or supergiants of intermediate and late spectral
Variable Magnitude Range (Brighter - Dimmer)5.000 - 6.000

Estimated Facts

Luminosity (x the Sun)7.0000000
Calculated Effective Temperature3,913 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars


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