Universe Guide

Omicron Aquarii (31 Aquarii) Star Facts

Omicron Aquarii Facts

Omicron Aquarii's Alternative Names

Omicron Aquarii (Omi Aqr) is the Bayer Classification for the star. The Bayer Classification was created by Johann Bayer in the early nineteenth century. The brightest star in the constellation is normally given the Alpha designation although there are exceptions such as Pollux which is Beta Geminorum.

The Id of the star in the Yale Bright Star Catalogue is HR8402. 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.

Omicron Aquarii has alternative name(s) :- Kae Hu, omi Aqr.

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 31 Aquarii with it shortened to 31 Aqr.

The Gould star designation is one that was designed by American astronomer, Benjamin Apthorp Gould. Gould stars are predominantly in the Southern and Equatorial constellations but do appear in northern constellations such as Bootes and Orion. The star has the designation 103 G. Aquarii. There are no stars with a Gould designation in Ursa Major for example.

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-02 5681.

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

Location of Omicron Aquarii

The location of the subgiant 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 Omicron Aquarii, the location is 22h 03m 18.83 and -02° 09` 19.2 .

Radial Velocity and Proper Motion of Omicron Aquarii

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 -11.16 ± 0.16 milliarcseconds/year towards the north and 24.66 ± 0.23 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 11.00 km/s with an error of about 2.90 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.

Omicron Aquarii 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 340.14 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 Omicron Aquarii

Omicron Aquarii Colour and Temperature

Omicron Aquarii has a spectral type of B7IVe. This means the star is a blue subgiant star. 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

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. 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 3.44. 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.

Using the 2007 distance, the star is roughly 27,538,222.39 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 7,348.00 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.

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Additional Omicron Aquarii Facts and Figures

Visual Facts

Primary / Proper / Traditional NameOmicron Aquarii
Alternative NamesOmi Aqr, Kae Hu, HD 209409, HIP 108874, HR 8402, 103 G. Aquarii, 31 Aquarii, 31 Aqr, BD-02 5681, omi Aqr
Spectral TypeB7IVe
Constellation's Main StarNo
Multiple Star SystemNo / Unknown
Star TypeSubgiant Star
GalaxyMilky Way
Absolute Magnitude -0.60 / -0.89
Visual / Apparent Magnitude4.74
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)22h 03m 18.83
Declination (Dec.)-02° 09` 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 Distance from Earth7.49 Parallax (milliarcseconds)
 435.47 Light Years
 133.51 Parsecs
 27,538,222.39 Astronomical Units
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
Semi-Major Axis8388.00
Stellar Luminosity (Lsun)340.14

Companions (Multi-Star and Exoplanets) Facts

Exoplanet CountNone/Unaware

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 Calculated Facts

Radius (x the Sun)3.44
Effective Temperature11,677 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

Comments and Questions

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