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Tau2 Gruis, HD216655, HIP113191

Tau2 Gruis is a white to yellow star that can be located in the constellation of Grus. Tau2 Gruis is the brightest star in Grus based on the Hipparcos 2007 apparent magnitude. The star can not be seen by the naked eye, you need a telescope to see it. The star has an estimated age of 6.40 Billion of Years but could be as young as 5.60 to 7.10 according to Hipparcos.

Tau2 Gruis is the Bayer Classification for the star. 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.

Location of Tau2 Gruis

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 Tau2 Gruis, the location is 22h 55m 16.35 and -48d 27` 57.4 .

Proper Motion of Tau2 Gruis

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 miliarcseconds/year towards the north and -227.04 ± 0.84 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Age, Radius) of Tau2 Gruis

Tau2 Gruis has a spectral type of G5. This means the star is a white to yellow star. The star is 7377.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24061.0698868800000000s. The star has a B-V Colour Index of 0.56 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 5,968 Kelvin.

Tau2 Gruis 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. 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.

The star has a companion star which is in orbit close by, it has at least the following companions in close orbit, .

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. It would take a spaceship travelling at the speed of light, 151.14 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 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.

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*.

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.

Tau2 Gruis Facts

Alternative Names

Bayer DesignationTau2 Gruis
Hipparcos Library I.D.113191
Henry Draper Designation216655

Visual Facts

Star Type star
Age6.40 Billion Years Old
Age Range5.60 - 7.10 Billion Years Old
Absolute Magnitude3.71 / 3.65
Visual / Apparent Magnitude7.04
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)22h 55m 16.35
Declination (Dec.)-48d 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 Revised Distance from Earth20.97 Parallax (milliarcseconds)
 155.54 Light Years
 47.69 Parsecs
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
Spectral TypeG5
Associated / Clustered StarsTau1 Gruis
Tau2 Gruis B
Tau3 Gruis
Colour(G) White to Yellow

Estimated Facts

Calculated Effective Temperature5,968 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

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