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Polaris Australis, Sigma Octantis, HD177482, HIP104382, HR7228

Polaris Australis (Sigma Octantis) is a blue to white pulsating star that can be located in the constellation of Octans. The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.

Sigma Octantis is the Bayer Classification for the star. The Id of the star in the Yale Bright Star Catalogue is HR7228. HIP104382 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD177482.

Polaris Australis has alternative name(s), sig Oct.

Location of Polaris Australis

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 Polaris Australis, the location is 21h 08m 46.01 and -88d 57` 23.4 .

Proper Motion of Polaris Australis

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 4.98 ± 0.26 miliarcseconds/year towards the north and 25.75 ± 0.31 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 11.90000 km/s with an error of about 2.80 km/s .

Physical Properties (Colour, Temperature, Radius) of Polaris Australis

Polaris Australis has a spectral type of F0III. This means the star is a blue to white star. The star is 7358.00000000 Parsecs from the Galactic Centre or terms of Light Years is 23999.0988515200000000s. The star has a B-V Colour Index of 0.28 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 7,322 Kelvin.

Polaris Australis Radius has been calculated as being 3.91 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,717,189.56.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 4.07. The figure is derived at by using the formula from SDSS and has been known to produce widely incorrect figures.

Polaris Australis Apparent and Absolute Magnitudes

Polaris Australis has an apparent magnitude of 5.45 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 0.86 If you used the 2007 Parallax value, you would get an absolute magnitude of 0.77. 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 Polaris Australis

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 12.07 which gave the calculated distance to Polaris Australis as 270.23 light years away from Earth or 82.85 parsecs. It would take a spaceship travelling at the speed of light, 270.23 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 11.61 which put Polaris Australis at a distance of 280.93 light years or 86.13 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 7,358.00 Parsecs or 23,999.10 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 Polaris Australis

The star is a pulsating Delta Scuti 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. Polaris Australis brightness ranges from a magnitude of 5.535 to a magnitude of 5.499 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.

Polaris Australis Facts

Alternative Names

Traditional/Proper NamePolaris Australis
Short Namesig Oct
Bayer DesignationSigma Octantis
Hipparcos Library I.D.104382
Yale Bright Star Catalogue (HR) Id7228
Henry Draper Designation177482

Visual Facts

Star Type star
Absolute Magnitude0.86 / 0.77
Visual / Apparent Magnitude5.45
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)21h 08m 46.01
Declination (Dec.)-88d 57` 23.4
Galactic Latitude-27.71 degrees
Galactic Longitude303.91 degrees
1997 Distance from Earth12.07 Parallax (milliarcseconds)
 270.23 Light Years
 82.85 Parsecs
2007 Revised Distance from Earth11.61 Parallax (milliarcseconds)
 280.93 Light Years
 86.13 Parsecs
Galacto-Centric Distance23,999.10 Light Years / 7,358.00 Parsecs
Proper Motion Dec.4.98 ± 0.26 milliarcseconds/year
Proper Motion RA.25.75 ± 0.31 milliarcseconds/year
B-V Index0.28
Radial Velocity11.90 ± 2.80 km/s
Spectral TypeF0III
Colour(F) blue to white

Variable Star Details

Variable Star ClassPulsating
Variable Star TypeDelta Scuti
Mean Variability Period in Days0.095
Variable Magnitude Range (Brighter - Dimmer)5.499 - 5.535

Estimated Facts

Calculated Effective Temperature7,322 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

Location of Polaris Australis in Octans

Polaris Australis (Sigma Octantis) Location in Octans

The map was generated using Night Vision, an awesome free application by Brian Simpson.

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