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Omicron Aquarii, 31 Aquarii, HD209409, HIP108874

Omicron Aquarii is a blue eruptive subgiant star that can be located in the constellation of Aquarius. Omicron Aquarii is the brightest star in Aquarius 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.

Omicron Aquarii is the Bayer Classification for the star. HIP108874 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD209409. The Id of the star in the Gould Star Catalogue is 103. Stars in the southern hemisphere are more likely to have a Gould Id than the northern hemisphere. For example, there are no Gould classified stars in Ursa Major.

Omicron Aquarii has alternative name(s), omi Aqr.

Location of Omicron Aquarii

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 Omicron Aquarii, the location is 22h 03m 18.83 and -02d09`19.2 .

Proper Motion of Omicron Aquarii

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 -11.16 ± 0.16 miliarcseconds/year towards the north and 24.66 ± 0.23 miliarcseconds/year east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of Omicron Aquarii

Omicron Aquarii has a spectral type of B7IVe. This means the star is a blue subgiant star. The star is 7348.00000000 Parsecs from the Galactic Centre or terms of Light Years is 23966.4825171200000000s. The star has a B-V Colour Index of -0.1 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 11,677 Kelvin.

Omicron Aquarii Radius has been calculated as being 3.01 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,092,816.55.km. However with the 2007 release of updated Hipparcos files, the radius is now calculated at being round 3.44. 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 -0.16 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

Omicron Aquarii Apparent and Absolute Magnitudes

Omicron Aquarii has an apparent magnitude of 4.74 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 -0.60 If you used the 2007 Parallax value, you would get an absolute magnitude of -0.89. 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 Omicron Aquarii

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 8.56 which gave the calculated distance to Omicron Aquarii as 381.03 light years away from Earth or 116.82 parsecs. It would take a spaceship travelling at the speed of light, 381.03 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 7.49 which put Omicron Aquarii at a distance of 435.47 light years or 133.51 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 7,348.00 Parsecs or 23,966.48 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 Omicron Aquarii

The star is a eruptive Gamma Cassiopeiae 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. Omicron Aquarii brightness ranges from a magnitude of 4.907 to a magnitude of 4.662 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.3 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.

Omicron Aquarii Facts

Alternative Names

Flamsteed Name31 Aquarii
Flamsteed Short Name31 Aqr
Short Nameomi Aqr
Bayer DesignationOmicron Aquarii
Hipparcos Library I.D.108874
Bonner DurchmusterungBD-02 5681
Gould I.D.103
Henry Draper Designation209409

Visual Facts

Star Typesubgiant star
Absolute Magnitude-0.60 / -0.89
Visual / Apparent Magnitude4.74
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)22h 03m 18.83
Declination (Dec.)-02d09`19.2
Galactic Latitude-42.67 degrees
Galactic Longitude57.44 degrees
1997 Distance from Earth8.56 Parallax (milliarcseconds)
 381.03 Light Years
 116.82 Parsecs
2007 Revised Distance from Earth7.49 Parallax (milliarcseconds)
 435.47 Light Years
 133.51 Parsecs
Galacto-Centric Distance23,966.48 Light Years / 7,348.00 Parsecs
Proper Motion Dec.-11.16 ± 0.16 milliarcseconds/year
Proper Motion RA.24.66 ± 0.23 milliarcseconds/year
B-V Index-0.10
Radial Velocity11.00 ± 2.90 km/s
Iron Abundance-0.16 ± 9.99 Fe/H
Spectral TypeB7IVe
Colour(B) blue

Variable Star Details

Variable Star ClassEruptive
Variable Star TypeGamma Cassiopeiae
Mean Variability Period in Days0.268
Variable Magnitude Range (Brighter - Dimmer)4.662 - 4.907

Estimated Facts

Calculated Effective Temperature11,677 Kelvin

Sources and Links

SIMBAD SourceLink

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