Universe Guide


HR 8770 - HD217833 - HIP113797

HR 8770 is a blue rotating giant star that can be located in the constellation of Cassiopeia. HIP113797 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD217833. HR 8770 has alternative name(s), V638_Cas.

Location of HR 8770

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 HR 8770, the location is 23h 02m 43.88 and +55d14`10.9 .

Proper Motion of HR 8770

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 004.24 ± 000.43 towards the north and 016.67 ± 000.57 east if we saw them in the horizon.

Physical Properties (Colour, Temperature, Radius) of HR 8770

HR 8770 has a spectral type of B9III He wk. This means the star is a blue giant star. The star has a B-V Colour Index of -0.07 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 10,845 Kelvin.

HR 8770 has been calculated as 2.93 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,036,717.89.km.

HR 8770 Apparent and Absolute Magnitudes

HR 8770 has an apparent magnitude of 6.51 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 -0.22 If you used the 2007 Parallax value, you would get an absolute magnitude of -0.57. 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 HR 8770

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 4.51 which gave the calculated distance to HR 8770 as 723.20 light years away from Earth or 221.73 parsecs. It would take a spaceship travelling at the speed of light, 723.20 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 3.84 which put HR 8770 at a distance of 849.38 light years or 260.42 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.

Variable Type of HR 8770

The star is a rotating Alpha2 Canum Venaticorum 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. HR 8770 brightness ranges from a magnitude of 7.000 to a magnitude of 6.000 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 5.0 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 Stellar Age, Metallicity or Mass is from the E.U. Exoplanets. The information was obtained as of 12th Feb 2017.

HR 8770 Facts

Alternative Names

Traditional NameHR 8770
Short NameV638 Cas
Hipparcos Library I.D.113797
Bonner DurchmusterungBD+54 2900
Henry Draper Designation217833

Visual Facts

Star Typegiant star
Absolute Magnitude-0.22 / -0.57
Apparent Magnitude6.51
Right Ascension (R.A.)23h 02m 43.88
Declination (Dec.)+55d14`10.9
1997 Distance from Earth4.51 Parallax (milliarcseconds)
 723.20 Light Years
 221.73 Parsecs
2007 Revised Distance from Earth3.84 Parallax (milliarcseconds)
 849.38 Light Years
 260.42 Parsecs
Proper Motion Dec.4.24 ± 0.43 milliarcseconds/year
Proper Motion RA.16.67 ± 0.57 milliarcseconds/year
B-V Index-0.07
Spectral TypeB9III He wk
Colour(B) blue

Variable Star Details

Variable Star ClassRotating
Variable Star TypeAlpha2 Canum Venaticorum
Mean Variability Period in Days5.000
Variable Magnitude Range (Brighter - Dimmer)6.000 - 7.000

Estimated Facts

Radius (x the Sun)2.93
Calculated Effective Temperature10,845 Kelvin

Sources and Links

SIMBAD SourceLink

Related Stars

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
217833+54 2900.0A6.600002.0000030.00000B9Blue/White

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