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Tau2 Gruis

Tau2 Gruis Facts

Tau2 Gruis's Alternative Names

(Tau2 Gruis) 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.

HIP113191 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD216655.

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

Location of Tau2 Gruis

The location of the multiple star system 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 Tau2 Gruis, the location is 22h 55m 16.35 and -48° 27` 57.4 .

Radial Velocity and Proper Motion of Tau2 Gruis

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 62.29 ± 0.71 milliarcseconds/year towards the north and -227.04 ± 0.84 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 1.10 km/s with an error of about 0.30 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.

Tau2 Gruis 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 3.07 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, Age) of Tau2 Gruis

Tau2 Gruis Colour and Temperature

Tau2 Gruis has a spectral type of G5. This means the star is a yellow multiple star system. The star has a B-V Colour Index of 0.56 which means the star's temperature is about 5,968 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu at being .

Tau2 Gruis Radius

Radius has been calculated as being 1.58 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 1,100,762.89.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 1.63. 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 -0.20 with an error value of 0.08 Fe/H with the Sun has a value of 1 to put it into context.

The stars age according to Hipparcos data files put the star at an age of about 6.40 Billion years old but could be between 5.60 and 7.10 Billion years old. In comparison, the Sun's age is about 4.6 Billion Years Old.

Tau2 Gruis Apparent and Absolute Magnitudes

Tau2 Gruis has an apparent magnitude of 7.04 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 3.71 If you used the 2007 Parallax value, you would get an absolute magnitude of 3.65. 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 Tau2 Gruis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 21.58 which gave the calculated distance to Tau2 Gruis as 151.14 light years away from Earth or 46.34 parsecs. If you want that in miles, it is 101,356,997,307.

In 2007, Hipparcos data was revised with a new parallax of 20.97 which put Tau2 Gruis at a distance of 155.54 light years or 47.69 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 9,836,700.07 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 7,377.00 Parsecs or 24,061.07 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 Tau2 Gruis

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)
Walking426,076,927,618.67
Car120869,230,920.62
Airbus A380736141,722,432.71
Speed of Sound (Mach 1)767.269135,946,728.56
Concorde (Mach 2)1,534.5467,973,275.69
New Horizons Probe33,0003,160,839.71
Speed of Light670,616,629.00155.54

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 Tau2 Gruis Facts and Figures

Visual Facts


Primary / Proper / Traditional NameTau2 Gruis
Alternative NamesHD 216655, HIP 113191
Spectral TypeG5
Constellation's Main StarNo
Multiple Star SystemYes
Star TypeMultiple Star System
ColourYellow
GalaxyMilky Way
ConstellationGrus
Age6.40 Billion Years Old
Age Range5.60 - 7.10 Billion Years Old
Absolute Magnitude 3.71 / 3.65
Visual / Apparent Magnitude7.04
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)22h 55m 16.35
Declination (Dec.)-48° 27` 57.4
Galactic Latitude-59.01 degrees
Galactic Longitude341.62 degrees
1997 Distance from Earth21.58 Parallax (milliarcseconds)
 151.14 Light Years
 46.34 Parsecs
2007 Distance from Earth20.97 Parallax (milliarcseconds)
 155.54 Light Years
 47.69 Parsecs
 9,836,700.07 Astronomical Units
Galacto-Centric Distance24,061.07 Light Years / 7,377.00 Parsecs
Proper Motion Dec.62.29 ± 0.71 milliarcseconds/year
Proper Motion RA.-227.04 ± 0.84 milliarcseconds/year
B-V Index0.56
Radial Velocity1.10 ± 0.30 km/s
Iron Abundance-0.20 ± 0.08 Fe/H
Eccentricity0.54
Semi-Major Axis12648.00
Stellar Luminosity (Lsun)3.07
Associated / Clustered StarsTau1 Gruis
Tau2 Gruis B
Tau3 Gruis

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Estimated Calculated Facts


Radius (x the Sun)1.63
Effective Temperature5,968 Kelvin

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
216655-4913996.2A7.60000-229.0000059.00000G0Yellow
B7.900001959

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