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Asellus Secundus (Iota Bootis) - HD125161 - HIP69713

Asellus Secundus (Iota Bootis) is a blue main sequence dwarf star that can be located in the constellation of Bootes. Iota Bootis is the Bayer Classification for the star. HIP69713 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD125161. Asellus Secundus has alternative name(s), 21 Bootis , 21 Boo.

Location of Asellus Secundus

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 Asellus Secundus, the location is 14h 16m 10.07 and +51d22`01.3 .

Proper Motion of Asellus Secundus

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 088.72 ± 000.16 towards the north and -149.39 ± 000.19 east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of Asellus Secundus

Asellus Secundus has a spectral type of A9V. This means the star is a blue main sequence dwarf star. 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 7,593 Kelvin.

Asellus Secundus has been calculated as 1.80 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,254,693.55.km.

Asellus Secundus Apparent and Absolute Magnitudes

Asellus Secundus has an apparent magnitude of 4.75 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 2.38 If you used the 2007 Parallax value, you would get an absolute magnitude of 2.43. 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 Asellus Secundus

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 33.54 which gave the calculated distance to Asellus Secundus as 97.25 light years away from Earth or 29.82 parsecs. It would take a spaceship travelling at the speed of light, 97.25 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 34.40 which put Asellus Secundus at a distance of 94.81 light years or 29.07 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.

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 Stellar Age, Metallicity or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

Asellus Secundus Facts

Alternative Names

Traditional NameAsellus Secundus
Short Name21 Boo
Bayer DesignationIota Bootis
Alternative Name(s)21 Bootis
Hipparcos Library I.D.69713
Bonner DurchmusterungBD+52 1784
Henry Draper Designation125161

Visual Facts

Star Typemain sequence dwarf star
Absolute Magnitude2.38 / 2.43
Apparent Magnitude4.75
Right Ascension (R.A.)14h 16m 10.07
Declination (Dec.)+51d22`01.3
1997 Distance from Earth33.54 Parallax (milliarcseconds)
 97.25 Light Years
 29.82 Parsecs
2007 Revised Distance from Earth34.40 Parallax (milliarcseconds)
 94.81 Light Years
 29.07 Parsecs
Proper Motion Dec.88.72 ± 0.16 milliarcseconds/year
Proper Motion RA.-149.39 ± 0.19 milliarcseconds/year
B-V Index0.23
Spectral TypeA9V
Colour(A) blue

Estimated Facts

Radius (x the Sun)1.80
Calculated Effective Temperature7,593 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

Multi-Star System

The star has been identified as being a multi-star system, one in which there is at least one star in close orbit to another star or two or more stars orbiting a central point. The stars may be of equal mass, unequal mass where one star is stronger than the other or be in groups orbiting a central point which doesn't necessarily have to be a star. More information can be found on my dedicated multiple star systems page. The source of the info is Simbad. The file is dated 2000 so any differences between this and any other source will be down to the actual source from where the information came from.


Proper Motion mas/yr
H.D. IdB.D. IdStar CodeMagnitudeR.A.Dec.SpectrumColourYear
125161+52 1784.0A4.90000-153.0000088.00000A5White
234121+52 1785.0B7.50000-152.0000068.00000A2White1836
C12.600001911

Location of Asellus Secundus in Bootes


Asellus Secundus (Iota Bootis) Location in Bootes

The map was generated using Night Vision, an awesome free application by Brian Simpson.


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