Universe Guide

Tau Cancri (72 Cancri) Star Facts

Tau Cancri Facts

  • Tau Cancri is a giant star that can be located in the constellation of Cancer. The description is based on the spectral class.
  • Tau Cancri is not part of the constellation outline but is within the borders of the constellation.
  • Based on the spectral type (G8III) of the star, the star's colour is yellow .
  • The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.
  • Using the most recent figures given by the 2007 Hipparcos data, the star is 273.63 light years away from us. Distance

Tau Cancri's Alternative Names

Tau Cancri (Tau Cnc) 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 HR3621. HIP44818 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD78235.

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 72 Cancri. The Flamsteed name can be shortened to 72 Cnc.

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+30 1817.

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

Location of Tau Cancri

The location of the giant 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 Cancri, the location is 09h 08m 00.07 and +29° 39` 15.2 .

Radial Velocity and Proper Motion of Tau Cancri

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 2.79 ± 0.24 milliarcseconds/year towards the north and -32.51 ± 0.39 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 -14.06000 km/s with an error of about 0.21 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 Cancri

Tau Cancri Colour and Temperature

Based on the star's spectral type of G8III , Tau Cancri's colour and type is yellow giant star. The star has a B-V Colour Index of 0.88 which means the star's temperature is about 5,096 Kelvin. The temperature was calculated using information from Morgans @ Uni.edu.

Tau Cancri 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 52.18 that I have given is based on the value in the Simbad Hipparcos Extended Catalogue at the University of Strasbourg from 2012.

Tau Cancri Radius

Tau Cancri estimated radius has been calculated as being 7.88 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 5,481,760.51.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 8.287751355349727602168627503. 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 Cancri Iron Abundance

Tau Cancri Iron Abundance is -0.10 with an error value of 0.02 Fe/H with the Sun has a value of 1 to put it into context. The value comes from the Hipparcos Extended Catalog.

Tau Cancri Apparent and Absolute Magnitudes

Tau Cancri has an apparent magnitude of 5.42 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 0.91 If you used the 2007 Parallax value, you would get an absolute magnitude of 0.80. 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 Cancri

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 12.56000 which gave the calculated distance to Tau Cancri as 259.68 light years away from Earth or 79.62 parsecs. If you want that in miles, it is about 1,526,561,436,908,319.84, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 11.92000 which put Tau Cancri at a distance of 273.63 light years or 83.89 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 17,303,434.02 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 7,461.00 Parsecs or 24,335.05 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 Cancri

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 A380736249,321,777.44
Speed of Sound (Mach 1)767.269239,161,008.97
Concorde (Mach 2)1,534.54119,580,348.63
New Horizons Probe33,0005,560,631.16
Speed of Light670,616,629.00273.63

Meteor Showers Radiating from near Tau Cancri

The Tau Cancrids Meteor Shower radiants from a point near this star. The meteor shower runs typically between Oct 9-25 with a peak date of Oct 17. The speed of a meteor in the shower is 67 Km/s.

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 Cancri Facts and Figures

Visual Facts

Primary / Proper / Traditional NameTau Cancri
Alternative NamesTau Cnc, HD 78235, HIP 44818, HR 3621, 72 Cancri, 72 Cnc, BD+30 1817
Spectral TypeG8III
Constellation's Main StarNo
Multiple Star SystemNo / Unknown
Star TypeGiant Star
GalaxyMilky Way
Absolute Magnitude 0.91 / 0.80
Visual / Apparent Magnitude5.42
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)09h 08m 00.07
Declination (Dec.)+29° 39` 15.2
Galactic Latitude41.27488230 degrees
Galactic Longitude196.07473454 degrees
1997 Distance from Earth12.56000 Parallax (milliarcseconds)
 259.68 Light Years
 79.62 Parsecs
2007 Distance from Earth11.92000 Parallax (milliarcseconds)
 273.63 Light Years
 83.89 Parsecs
 17,303,434.02 Astronomical Units
Galacto-Centric Distance24,335.05 Light Years / 7,461.00 Parsecs
Proper Motion Dec.2.79000 ± 0.24000 milliarcseconds/year
Proper Motion RA.-32.51000 ± 0.39000 milliarcseconds/year
B-V Index0.88
Radial Velocity-14.06000 ± 0.21 km/s
Iron Abundance-0.1000 ± 0.02 Fe/H
Semi-Major Axis9158.0000000
Stellar Luminosity (Lsun)52.1800000

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

Estimated Calculated Facts

Radius (x the Sun)8.29
Effective Temperature5,096 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

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