Mimosa (Beta Crucis) is a blue pulsating giant star that can be located in the constellation of Crux. The description is based on the spectral class. Mimosa is a main star of the constellation.
Mimosa is the 20th brightest star in the night sky and the 3rd 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.
Mimosa's Alternative Names
Beta Crucis (Bet Cru) is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR4853. HIP62434 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD111123.
Mimosa has alternative name(s) :- Becrux, bet Cru.
More details on star alternative names can be found at Star Names .
Location of Mimosa
The location of the 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 star is compared to the celestial equator and is expressed in degrees. For Mimosa, the location is 12h 47m 43.32 and -59° 41` 19.4 .
Radial Velocity and Proper Motion of Mimosa
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 -16.18 ± 0.61 miliarcseconds/year towards the north and -42.97 ± 0.98 miliarcseconds/year east if we saw them in the horizon.
The Radial Velocity, that is the speed at which the star is moving away/towards the Sun is 10.30 km/s with an error of about 0.20 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.
Mimosa 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 19,920.27 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 Mimosa
Mimosa has a spectral type of B0.5III. This means the star is a blue giant star. The star is 7,343.00 Parsecs from the Galactic Centre or terms of Light Years is 23,950.17 s. The star has a B-V Colour Index of -0.23 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 19,982 Kelvin.
Mimosa Radius has been calculated as being 4.74 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 3,297,223.65.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 3.75. 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 -0.08 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.
Mimosa Apparent and Absolute Magnitudes
Mimosa has an apparent magnitude of 1.25 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 -3.92 If you used the 2007 Parallax value, you would get an absolute magnitude of -3.41. 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 Mimosa
Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 9.25 which gave the calculated distance to Mimosa as 352.61 light years away from Earth or 108.11 parsecs. It would take a spaceship travelling at the speed of light, 352.61 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 11.71 which put Mimosa at a distance of 278.53 light years or 85.40 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 7,343.00 Parsecs or 23,950.17 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 Mimosa
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. Mimosa brightness ranges from a magnitude of 1.165 to a magnitude of 1.145 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.2 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.
Alternative Names Beta Crucis, Bet Cru, Becrux, HD 111123, HIP 62434, HR 4853, bet Cru
Spectral Type B0.5III
Constellation's Main Star Yes
Multiple Star System Yes
Star Type Giant Star
Colour blue
Galaxy Milky Way
Constellation Crux
Absolute Magnitude -3.92 / -3.41
Visual / Apparent Magnitude 1.25
Naked Eye Visible Yes - Magnitudes
Right Ascension (R.A.) 12h 47m 43.32
Declination (Dec.) -59° 41` 19.4
Galactic Latitude 3.18 degrees
Galactic Longitude 302.46 degrees
1997 Distance from Earth 9.25 Parallax (milliarcseconds)
352.61 Light Years
108.11 Parsecs
2007 Distance from Earth 11.71 Parallax (milliarcseconds)
278.53 Light Years
85.40 Parsecs
Galacto-Centric Distance 23,950.17 Light Years / 7,343.00 Parsecs
Proper Motion Dec. -16.18 ± 0.61 milliarcseconds/year
Proper Motion RA. -42.97 ± 0.98 milliarcseconds/year
B-V Index -0.23
Radial Velocity 10.30 ± 0.20 km/s
Iron Abundance -0.08 ± 9.99 Fe/H
Eccentricity 0.08
Semi-Major Axis 6793.00
Stellar Luminosity (Lsun) 19,920.27
Brightest in Night Sky 20th
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