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Tau Bootis, 4 Bootis, HD120136, HIP67275

Tau Bootis is a blue to white main sequence dwarf star that can be located in the constellation of Bootes. Tau Bootis is the brightest star in Bootes 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. The star has an estimated age of 2.10 Billion of Years but could be as young as 1.50 to 2.50 according to Hipparcos.

Tau Bootis is the Bayer Classification for the star. HIP67275 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD120136. The Gliese ID of the star is Gliese GL527A. The star was part of the original catalogue devised by German Astronomer Wilheim Gliese of stars located within 20 parsecs of Earth. Ref : Star Names.

Tau Bootis has alternative name(s), 4 Boo, Tau Boo. Tau Bootis has at least 1 Extrasolar Planets believed to be in orbit around the star.

Location of Tau Bootis

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 Tau Bootis, the location is 13h 47m 16.04 and +17d27`24.4 .

Proper Motion of Tau Bootis

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 53.49 ± 0.13 miliarcseconds/year towards the north and -479.53 ± 0.19 miliarcseconds/year east if we saw them in the horizon.

Tau Bootis 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 2.0000000 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, Metallicity, Age, Mass, Radius) of Tau Bootis

Tau Bootis has a spectral type of F7V. This means the star is a blue to white main sequence dwarf star. The star is 7396.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24123.0409222400000000s. The star has a B-V Colour Index of 0.5 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 6,285 Kelvin.

Tau Bootis Radius has been calculated as being 1.55 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,078,307.46.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 1.55. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures. The star's solar mass is 1.30 times that of the Sun's. The Sun's Mass is 1,989,100,000,000,000,000,000 billion kg. which to calculate using this website is too large. To give idea of size, the Sun is 99.86% the mass of the solar system.

The star's metallicity is 0.280000, this value is the fractional amount of the star that is not Hydrogen (X) or Helium (Y). An older star would have a high metallicity whereas a new star would have a lower one.

The stars age according to Hipparcos data files put the star at an age of about 2.10 Billion years old but could be between 1.50 and 2.50 Billion years old. In comparison, the Sun's age is about 4.6 Billion Years Old.

Tau Bootis Apparent and Absolute Magnitudes

Tau Bootis has an apparent magnitude of 4.50 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 3.53 If you used the 2007 Parallax value, you would get an absolute magnitude of 3.53. 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 Tau Bootis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 64.12 which gave the calculated distance to Tau Bootis as 50.87 light years away from Earth or 15.60 parsecs. It would take a spaceship travelling at the speed of light, 50.87 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 64.03 which put Tau Bootis at a distance of 50.94 light years or 15.62 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 7,396.00 Parsecs or 24,123.04 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

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.

Tau Bootis Facts

Alternative Names

Flamsteed Name4 Bootis
Short Name4 Boo, Tau Boo
Bayer DesignationTau Bootis
Hipparcos Library I.D.67275
Bonner DurchmusterungBD+18 2782
Gliese ID527A
Henry Draper Designation120136

Visual Facts

Star Typemain sequence dwarf star
Age2.10 Billion Years Old
Age Range1.50 - 2.50 Billion Years Old
Metalicity0.2800
Absolute Magnitude3.53 / 3.53
Visual / Apparent Magnitude4.50
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)13h 47m 16.04
Declination (Dec.)+17d27`24.4
Galactic Latitude73.89 degrees
Galactic Longitude358.94 degrees
1997 Distance from Earth64.12 Parallax (milliarcseconds)
 50.87 Light Years
 15.60 Parsecs
2007 Revised Distance from Earth64.03 Parallax (milliarcseconds)
 50.94 Light Years
 15.62 Parsecs
Galacto-Centric Distance24,123.04 Light Years / 7,396.00 Parsecs
Proper Motion Dec.53.49 ± 0.13 milliarcseconds/year
Proper Motion RA.-479.53 ± 0.19 milliarcseconds/year
B-V Index0.50
Radial Velocity-16.03 ± 0.15 km/s
Iron Abundance0.24 ± 9.99 Fe/H
Spectral TypeF7V
Colour(F) blue to white

Companions (Multi-Star and Exoplanets) Facts

Exoplanet Count1

Estimated Facts

Luminosity (x the Sun)2.0000000
Calculated Effective Temperature6,285 Kelvin
Mass Compared to the Sun1.30
Metallicity0.28000

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
120136+18 2782.0A4.50000-482.0000034.00000F5Yellow/White
B11.10000-458.00000-12.000001958

List of Extrasolar Planets orbiting Tau Bootis


NameStatusMass (Jupiters)Orbital Period (Days)EccentricityDiscoveredSemi-Major AxisPeriastronInclination
Tau Boo BConfirmed5.843.3120.078719960.046218.00045.000

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