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AC Hercules, HD170756, HIP90697

AC Hercules is a blue to white pulsating supergiant star that can be located in the constellation of Hercules. 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.

AC Hercules's Alternative Names

HIP90697 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD170756.

AC Hercules has alternative name(s) :- , AC Her.

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+21 3459.

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

Location of AC Hercules

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 AC Hercules, the location is 18h 30m 16.24 and +21° 52` 00.6 .

Proper Motion of AC Hercules

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 -0.18 ± 0.86 miliarcseconds/year towards the north and -2.82 ± 1.40 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 -30.00000 km/s with an error of about 3.10 km/s .

Physical Properties (Colour, Temperature) of AC Hercules

AC Hercules has a spectral type of F4Ibpvar. This means the star is a blue to white supergiant star. The star has a B-V Colour Index of 0.72 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 5,603 Kelvin.

AC Hercules Radius has been calculated as being 43.26 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 30,100,797.45.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 57.29. 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 -1.16 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

AC Hercules Apparent and Absolute Magnitudes

AC Hercules has an apparent magnitude of 7.57 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 -3.20 If you used the 2007 Parallax value, you would get an absolute magnitude of -3.81. 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 AC Hercules

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 0.70 which gave the calculated distance to AC Hercules as 4659.48 light years away from Earth or 1428.57 parsecs. It would take a spaceship travelling at the speed of light, 4659.48 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 0.53 which put AC Hercules at a distance of 6154.03 light years or 1886.79 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 AC Hercules

The star is a pulsating RV Tauri 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 Hercules brightness ranges from a magnitude of 8.501 to a magnitude of 7.318 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 75.3 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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AC Hercules Facts

Visual Facts


Primary / Proper / Traditional NameAC Hercules
Alternative NamesHD 170756, HIP 90697, BD+21 3459, AC Her
Spectral TypeF4Ibpvar
Multiple Star SystemNo / Unknown
Star Type very luminous Supergiant Star
Colour blue to white
GalaxyMilky Way
ConstellationHercules
Absolute Magnitude-3.20 / -3.81
Visual / Apparent Magnitude7.57
Naked Eye VisibleRequires a 7x50 Binoculars - Magnitudes
Right Ascension (R.A.)18h 30m 16.24
Declination (Dec.)+21° 52` 00.6
Galactic Latitude14.24 degrees
Galactic Longitude50.49 degrees
1997 Distance from Earth0.70 Parallax (milliarcseconds)
 4659.48 Light Years
 1428.57 Parsecs
2007 Distance from Earth0.53 Parallax (milliarcseconds)
 6154.03 Light Years
 1886.79 Parsecs
Proper Motion Dec.-0.18 ± 0.86 milliarcseconds/year
Proper Motion RA.-2.82 ± 1.40 milliarcseconds/year
B-V Index0.72
Radial Velocity-30.00 ± 3.10 km/s
Iron Abundance-1.16 ± 9.99 Fe/H

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassPulsating
Variable Star TypeRV Tauri
Mean Variability Period in Days75.300
Variable Magnitude Range (Brighter - Dimmer)7.318 - 8.501

Estimated Facts


Calculated Effective Temperature5,603 Kelvin

Sources and Links


SIMBAD SourceLink

Related Stars


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