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Tau1 Arietis, 61 Arietis, HD20756, HIP15627, HR1005

Tau1 Arietis is a blue eclipsing subgiant star that can be located in the constellation of Aries. The description is based on the spectral class. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

Tau1 Arietis's Alternative Names

Tau1 Arietis (Tau Ari) is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR1005. 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.

Flamsteed designations are named after the creator, Sir John Flamsteed. Sir John numbered the stars in the constellation with a number and the latin name, this star's Flamsteed designation is 61 Arietis with it shortened to 61 Ari.

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+20 543.

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

Location of Tau1 Arietis

The location of the 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 star is compared to the celestial equator and is expressed in degrees. For Tau1 Arietis, the location is 03h 21m 13.61 and +21° 08` 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. The Radial Velocity, that is the speed at which the star is moving away/towards us is 14.70000 km/s with an error of about 0.90 km/s .

Tau1 Arietis 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 234.24 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) of Tau1 Arietis

Tau1 Arietis has a spectral type of B5IV. This means the star is a blue subgiant star. The star is 7,529.00 Parsecs from the Galactic Centre or terms of Light Years is 24,556.84 s. 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. 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 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.

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Tau1 Arietis Facts

Visual Facts

Primary / Proper / Traditional NameTau1 Arietis
Alternative NamesTau Ari, HD 20756, HIP 15627, HR 1005, 61 Arietis, 61 Ari, BD+20 543, tau01 Ari
Spectral TypeB5IV
Multiple Star SystemYes
Star TypeSubgiant Star
Colour blue
GalaxyMilky Way
Absolute Magnitude-0.49 / -0.70
Visual / Apparent Magnitude5.27
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)03h 21m 13.61
Declination (Dec.)+21° 08` 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 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
Semi-Major Axis7155.00
Stellar Luminosity (Lsun)234.24
Associated / Clustered StarsTau2 Arietis

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

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

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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