HIP33791 is the reference name for the star in the Hipparcos Star Catalogue.
AC Monocerotis has alternative name(s) :- AC Mon, AC Mon.
More details on objects' alternative names can be found at Star Names .
The location of the variable 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 AC Monocerotis, the location is 07h 00m 59.82 and -08° 42` 32.4 .
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 3.37 ± 1.45 milliarcseconds/year towards the north and -1.44 ± 2.15 milliarcseconds/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 40.50 km/s with an error of about 1.78 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.
AC Monocerotis has a spectral type of F7.5. This means the star is a yellow to white variable star.
AC Monocerotis has an apparent magnitude of 10.38 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 0.15 If you used the 2007 Parallax value, you would get an absolute magnitude of 1.10. 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.
Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 0.90 which gave the calculated distance to AC Monocerotis as 3624.04 light years away from Earth or 1111.11 parsecs. It would take a spaceship travelling at the speed of light, 3624.04 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 1.39 which put AC Monocerotis at a distance of 2346.50 light years or 719.42 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 148,389,992.91 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 is a pulsating Delta Cepheid 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. AC Monocerotis brightness ranges from a magnitude of 10.619 to a magnitude of 9.891 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 8.0 days (variability).
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.
|Primary / Proper / Traditional Name||AC Monocerotis|
|Alternative Names||AC Mon, HIP 33791, AC Mon|
|Constellation's Main Star||No|
|Multiple Star System||No / Unknown|
|Star Type||Variable Star|
|Colour||Yellow - White|
|Absolute Magnitude||0.15 / 1.10|
|Visual / Apparent Magnitude||10.38|
|Naked Eye Visible||Requires a 4.5 - 6 Inch Telescope - Magnitudes|
|Right Ascension (R.A.)||07h 00m 59.82|
|Declination (Dec.)||-08° 42` 32.4|
|Galactic Latitude||-1.85 degrees|
|Galactic Longitude||221.77 degrees|
|1997 Distance from Earth||0.90 Parallax (milliarcseconds)|
|3624.04 Light Years|
|2007 Distance from Earth||1.39 Parallax (milliarcseconds)|
|2346.50 Light Years|
|148,389,992.91 Astronomical Units|
|Proper Motion Dec.||3.37 ± 1.45 milliarcseconds/year|
|Proper Motion RA.||-1.44 ± 2.15 milliarcseconds/year|
|Radial Velocity||40.50 ± 1.78 km/s|
|Variable Star Class||Pulsating|
|Variable Star Type||Delta Cepheid|
|Mean Variability Period in Days||8.013|
|Variable Magnitude Range (Brighter - Dimmer)||9.891 - 10.619|
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