Universe Guide


Tau1 Arietis, 61 Arietis, HD20756, HIP15627

Tau1 Arietis is a blue eclipsing subgiant star that can be located in the constellation of Aries. Tau1 Arietis is the brightest star in Aries 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.

Tau1 Arietis is the Bayer Classification for the star. HIP15627 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD20756.

Tau1 Arietis has alternative name(s), tau01 Ari.

Location of Tau1 Arietis

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 Tau1 Arietis, the location is 03h 21m 13.61 and +21d08`49.7 .

Proper Motion of Tau1 Arietis

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 -21.80 ± 0.53 miliarcseconds/year towards the north and 20.98 ± 0.73 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of Tau1 Arietis

Tau1 Arietis has a spectral type of B5IV. This means the star is a blue subgiant star. The star is 7529.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24556.8381697600000000s. The star has a B-V Colour Index of -0.06 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 10,611 Kelvin.

Tau1 Arietis Radius has been calculated as being 3.46 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,409,239.70.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 3.81. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Tau1 Arietis Apparent and Absolute Magnitudes

Tau1 Arietis has an apparent magnitude of 5.27 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 -0.49 If you used the 2007 Parallax value, you would get an absolute magnitude of -0.70. 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 Tau1 Arietis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 7.06 which gave the calculated distance to Tau1 Arietis as 461.99 light years away from Earth or 141.64 parsecs. It would take a spaceship travelling at the speed of light, 461.99 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 6.41 which put Tau1 Arietis at a distance of 508.84 light years or 156.01 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 7,529.00 Parsecs or 24,556.84 Light Years. The Galacto-Centric Distance is the distance from the star to the Centre of the Galaxy which is Sagittarius A*.

Variable Type of Tau1 Arietis

The star is a eclipsing W Ursae Majoris variable type which means that its size changes over time. The Variable Type is usually named after the first star of that type to be spotted. This is a some uncertainty as to the type but the type mentioned is the current variable star classification for this star. Tau1 Arietis brightness ranges from a magnitude of 5.316 to a magnitude of 5.256 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 2.2 days (variability).

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.

Tau1 Arietis Facts

Alternative Names

Flamsteed Name61 Arietis
Flamsteed Short Name61 Ari
Short Nametau01 Ari
Bayer DesignationTau1 Arietis
Hipparcos Library I.D.15627
Bonner DurchmusterungBD+20 543
Henry Draper Designation20756

Visual Facts

Star Typesubgiant star
Absolute Magnitude-0.49 / -0.70
Visual / Apparent Magnitude5.27
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)03h 21m 13.61
Declination (Dec.)+21d08`49.7
Galactic Latitude-29.64 degrees
Galactic Longitude163.66 degrees
1997 Distance from Earth7.06 Parallax (milliarcseconds)
 461.99 Light Years
 141.64 Parsecs
2007 Revised Distance from Earth6.41 Parallax (milliarcseconds)
 508.84 Light Years
 156.01 Parsecs
Galacto-Centric Distance24,556.84 Light Years / 7,529.00 Parsecs
Proper Motion Dec.-21.80 ± 0.53 milliarcseconds/year
Proper Motion RA.20.98 ± 0.73 milliarcseconds/year
B-V Index-0.06
Radial Velocity14.70 ± 0.90 km/s
Spectral TypeB5IV
Colour(B) blue

Variable Star Details

Variable Star ClassEclipsing
Variable Star TypeW Ursae Majoris probably
Mean Variability Period in Days2.204
Variable Magnitude Range (Brighter - Dimmer)5.256 - 5.316

Estimated Facts

Calculated Effective Temperature10,611 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
20756+20 543.0A5.0000026.00000-23.00000B3Blue/White

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