Universe Guide

Tau Boötis (4 Boötis) Star Facts

Tau Boötis Facts

  • Tau Boötis is a main sequence star that can be located in the constellation of Bootes. The description is based on the spectral class.
  • Tau Boötis is not part of the constellation outline but is within the borders of the constellation.
  • Based on the spectral type (F7V) of the star, the star's colour is yellow to white .
  • 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 Boötis has at least 1 Extrasolar Planets believed to be in orbit around the star.
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 50.94 light years away from us. Distance

Tau Bootis's Alternative Names

Tau Bootis (Tau Boo) is the Bayer Classification for the star. The Bayer Classification was created by Johann Bayer in 1603. The brightest star in the constellation is normally given the Alpha designation, there are exceptions such as Pollux which is Beta Geminorum.

The Id of the star in the Yale Bright Star Catalogue is HR5185. 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 GL 527A. The star was part of the original catalogue devised by German Astronomer Wilheim Gliese of stars located within 20 parsecs of Earth. Star Names

Tau Bootis has alternative name(s) :- , 4 Boo, Tau Boo.

Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John named the stars in the constellation with a number and its latin name, this star's Flamsteed designation is 4 Bootis. The Flamsteed name can be shortened to 4 Boo.

BD number is the number that the star was filed under in the Durchmusterung or Bonner Durchmusterung, a star catalogue that was put together by the Bonn Observatory between 1859 to 1903. The star's BD Number is BD+18 2782.

More details on objects' alternative names can be found at Star Names .

Location of Tau Boötis

The location of the main sequence 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 object is compared to the celestial equator and is expressed in degrees. For Tau Boötis, the location is 13h 47m 16.04 and +17° 27` 24.4 .

Radial Velocity and Proper Motion of Tau Boötis

Proper Motion

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

Radial Velocity

The Radial Velocity, that is the speed at which the star is moving away/towards the Sun is -16.03000 km/s with an error of about 0.15 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.

Physical Properties of Tau Boötis

Tau Bootis Colour and Temperature

Based on the star's spectral type of F7V , Tau Bootis's colour and type is yellow to white main sequence star. The star's effective temperature is 6,387 Kelvin which is hotter than our own Sun's effective Temperature which is 5,777 Kelvin.

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 3.34 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Tau Bootis Radius

Tau Bootis estimated 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. 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 1.5497376563125726041724422037. The figure is derived at by using the formula from SDSS rather than peer reviewed papers. It has been known to produce widely incorrect figures.

Tau Bootis Mass

The Tau Bootis's solar mass is 1.30 times that of our star, the Sun. 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.

Tau Bootis Metalicity

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.

Tau Bootis Estimated Age

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 Boötis Apparent and Absolute Magnitudes

Tau Boötis 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 Boötis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 64.12000 which gave the calculated distance to Tau Boötis as 50.87 light years away from Earth or 15.60 parsecs. If you want that in miles, it is about 299,045,672,733,850.24, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 64.03000 which put Tau Boötis 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.

Using the 2007 distance, the star is roughly 3,221,833.82 Astronomical Units from the Earth/Sun give or take a few. An Astronomical Unit is the distance between Earth and the Sun. The number of A.U. is the number of times that the star is from the Earth compared to the Sun. 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*.

Travel Time to Tau Bootis

The time it will take to travel to this star is dependent on how fast you are going. U.G. has done some calculations as to how long it will take going at differing speeds. A note about the calculations, when I'm talking about years, I'm talking non-leap years only (365 days).

The New Horizons space probe is the fastest probe that we've sent into space at the time of writing. Its primary mission was to visit Pluto which at the time of launch (2006), Pluto was still a planet.

DescriptionSpeed (m.p.h.)Time (years)
Airbus A38073646,414,688.97
Speed of Sound (Mach 1)767.26944,523,121.72
Concorde (Mach 2)1,534.5422,261,531.85
New Horizons Probe33,0001,035,188.21
Speed of Light670,616,629.0050.94

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.

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Additional Tau Boötis Facts and Figures

Visual Facts

Primary / Proper / Traditional NameTau Bootis
Alternative NamesTau Boo, HD 120136, HIP 67275, HR 5185, 4 Bootis, 4 Boo, BD+18 2782, Gliese 527A, 4 Boo, Tau Boo
Spectral TypeF7V
Constellation's Main StarNo
Multiple Star SystemYes
Star Type Main Sequence Dwarf Star
ColourYellow - White
GalaxyMilky Way
Age2.10 Billion Years Old
Age Range1.50 - 2.50 Billion Years Old
Absolute Magnitude 3.53 / 3.53
Visual / Apparent Magnitude4.50
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)13h 47m 16.04
Declination (Dec.)+17° 27` 24.4
Galactic Latitude73.88799891 degrees
Galactic Longitude358.93911533 degrees
1997 Distance from Earth64.12000 Parallax (milliarcseconds)
 50.87 Light Years
 15.60 Parsecs
2007 Distance from Earth64.03000 Parallax (milliarcseconds)
 50.94 Light Years
 15.62 Parsecs
 3,221,833.82 Astronomical Units
Galacto-Centric Distance24,123.04 Light Years / 7,396.00 Parsecs
Proper Motion Dec.53.49000 ± 0.13000 milliarcseconds/year
Proper Motion RA.-479.53000 ± 0.19000 milliarcseconds/year
B-V Index0.5
Radial Velocity-16.03000 ± 0.15 km/s
Iron Abundance0.2400 ± 9.99 Fe/H
Semi-Major Axis7117.0000000
Stellar Luminosity (Lsun)3.3400000

Companions (Multi-Star and Exoplanets) Facts

Exoplanet Count1

Estimated Calculated Facts

Radius (x the Sun)1.55
Effective Temperature6,285 Kelvin
Mass Compared to the Sun1.30

Sources and Links

SIMBAD SourceLink

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

List of Extrasolar Planets orbiting Tau Bootis

NameStatusMass (Jupiters)Orbital Period (Days)EccentricityDiscoveredSemi-Major AxisPeriastronInclination
tau Boo bConfirmed0.553.3120.078719960.046218.40045.000

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