Universe Guide


Pi Aurigae, 35 Aurigae, HD40239, HIP28404

Pi Aurigae is a red pulsating luminous giant star that can be located in the constellation of Auriga. Pi Aurigae is the brightest star in Auriga 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.

Pi Aurigae is the Bayer Classification for the star. HIP28404 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD40239.

Pi Aurigae has alternative name(s), pi. Aur.

Location of Pi Aurigae

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 Pi Aurigae, the location is 05h 59m 56.10 and +45d56`12.3 .

Proper Motion of Pi Aurigae

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 -7.34 ± 0.28 miliarcseconds/year towards the north and -2.44 ± 0.62 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of Pi Aurigae

Pi Aurigae has a spectral type of M3IIvar. This means the star is a red luminous giant star. The star is 7615.00000000 Parsecs from the Galactic Centre or terms of Light Years is 24837.3386456000000000s. The star has a B-V Colour Index of 1.7 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 3,456 Kelvin.

Pi Aurigae Radius has been calculated as being 92.85 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 64,605,197.58.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 82.75. 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 0.03 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

Pi Aurigae Apparent and Absolute Magnitudes

Pi Aurigae has an apparent magnitude of 4.30 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 -2.76 If you used the 2007 Parallax value, you would get an absolute magnitude of -2.51. 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 Pi Aurigae

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 3.88 which gave the calculated distance to Pi Aurigae as 840.63 light years away from Earth or 257.73 parsecs. It would take a spaceship travelling at the speed of light, 840.63 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 4.34 which put Pi Aurigae at a distance of 751.53 light years or 230.41 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 7,615.00 Parsecs or 24,837.34 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 Pi Aurigae

The star is a pulsating Slow Irregular 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. Pi Aurigae brightness ranges from a magnitude of 4.361 to a magnitude of 4.250 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.1 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.

Pi Aurigae Facts

Alternative Names

Flamsteed Name35 Aurigae
Flamsteed Short Name35 Aur
Short Namepi. Aur
Bayer DesignationPi Aurigae
Hipparcos Library I.D.28404
Bonner DurchmusterungBD+45 1217
Henry Draper Designation40239

Visual Facts

Star Typeluminous giant star
Absolute Magnitude-2.76 / -2.51
Visual / Apparent Magnitude4.30
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)05h 59m 56.10
Declination (Dec.)+45d56`12.3
Galactic Latitude10.94 degrees
Galactic Longitude166.60 degrees
1997 Distance from Earth3.88 Parallax (milliarcseconds)
 840.63 Light Years
 257.73 Parsecs
2007 Revised Distance from Earth4.34 Parallax (milliarcseconds)
 751.53 Light Years
 230.41 Parsecs
Galacto-Centric Distance24,837.34 Light Years / 7,615.00 Parsecs
Proper Motion Dec.-7.34 ± 0.28 milliarcseconds/year
Proper Motion RA.-2.44 ± 0.62 milliarcseconds/year
B-V Index1.70
Radial Velocity0.71 ± 0.76 km/s
Iron Abundance0.03 ± 9.99 Fe/H
Spectral TypeM3IIvar
Colour(M) Red

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeSlow Irregular
Mean Variability Period in Days0.100
Variable Magnitude Range (Brighter - Dimmer)4.250 - 4.361

Estimated Facts

Calculated Effective Temperature3,456 Kelvin

Sources and Links

SIMBAD SourceLink

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