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AA Ceti, HD12180, HIP9258

AA Ceti is a blue eclipsing main sequence dwarf star that can be located in the constellation of Cetus. The description is based on the spectral class. The star can not be seen by the naked eye, you need a telescope to see it. The star has an estimated age of 1.50 Billion of Years but could be as young as 1.40 to 1.70 according to Hipparcos.

AA Ceti's Alternative Names

HIP9258 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD12180.

AA Ceti has alternative name(s) :- , AA Cet.

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

Location of AA Ceti

The location of the 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 star is compared to the celestial equator and is expressed in degrees. For AA Ceti, the location is 01h 59m 00.66 and -22° 55` 11.6 .

Radial Velocity and Proper Motion of AA Ceti

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 33.25 ± 2.17 miliarcseconds/year towards the north and 94.71 ± 3.63 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 the Sun is 32.70 km/s with an error of about 2.14 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 (Colour, Temperature, Age) of AA Ceti

AA Ceti has a spectral type of A7/8V + G. This means the star is a blue main sequence dwarf star. The star has a B-V Colour Index of 0.47 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 6,412 Kelvin.

AA Ceti Radius has been calculated as being 7.74 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 5,387,673.81.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 3.99. 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 0.07 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

The stars age according to Hipparcos data files put the star at an age of about 1.50 Billion years old but could be between 1.40 and 1.70 Billion years old. In comparison, the Sun's age is about 4.6 Billion Years Old.

AA Ceti Apparent and Absolute Magnitudes

AA Ceti has an apparent magnitude of 6.62 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 -0.05 If you used the 2007 Parallax value, you would get an absolute magnitude of 1.39. 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 AA Ceti

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 4.63 which gave the calculated distance to AA Ceti as 704.46 light years away from Earth or 215.98 parsecs. It would take a spaceship travelling at the speed of light, 704.46 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 8.99 which put AA Ceti at a distance of 362.81 light years or 111.23 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.

Variable Type of AA Ceti

The star is a eclipsing W Ursae Majoris/Contact systems of early (O-A) spectral type (subtype) 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. AA Ceti brightness ranges from a magnitude of 6.984 to a magnitude of 6.684 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.5 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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AA Ceti Facts

Visual Facts


Primary / Proper / Traditional NameAA Ceti
Alternative NamesHD 12180, HIP 9258, AA Cet
Spectral TypeA7/8V + G
Multiple Star SystemYes
Star Type main sequence Dwarf Star
Colour blue
GalaxyMilky Way
ConstellationCetus
Age1.50 Billion Years Old
Age Range1.40 - 1.70 Billion Years Old
Absolute Magnitude-0.05 / 1.39
Visual / Apparent Magnitude6.62
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)01h 59m 00.66
Declination (Dec.)-22° 55` 11.6
Galactic Latitude-74.14 degrees
Galactic Longitude201.27 degrees
1997 Distance from Earth4.63 Parallax (milliarcseconds)
 704.46 Light Years
 215.98 Parsecs
2007 Distance from Earth8.99 Parallax (milliarcseconds)
 362.81 Light Years
 111.23 Parsecs
Proper Motion Dec.33.25 ± 2.17 milliarcseconds/year
Proper Motion RA.94.71 ± 3.63 milliarcseconds/year
B-V Index0.47
Radial Velocity32.70 ± 2.14 km/s
Iron Abundance0.07 ± 9.99 Fe/H

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassEclipsing
Variable Star TypeW Ursae Majoris/Contact systems of early (O-A) spectral type (subtype)
Mean Variability Period in Days0.536
Variable Magnitude Range (Brighter - Dimmer)6.684 - 6.984

Estimated Facts


Calculated Effective Temperature6,412 Kelvin

Sources and Links


SIMBAD SourceLink

Multi-Star System

The star has been identified as being a multi-star system, one in which there is at least one star in close orbit to another star or two or more stars orbiting a central point. The stars may be of equal mass, unequal mass where one star is stronger than the other or be in groups orbiting a central point which doesn't necessarily have to be a star. More information can be found on my dedicated multiple star systems page. The source of the info is Simbad. The file is dated 2000 so any differences between this and any other source will be down to the actual source from where the information came from.


Proper Motion mas/yr
H.D. IdB.D. IdStar CodeMagnitudeR.A.Dec.SpectrumColourYear
12180-23 737.2A7.2000093.0000049.00000F2Yellow/White
B7.5000089.0000047.000001822

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