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Herchel's Garnet Star (Mu Cephei) Star Facts

Herchel's Garnet Star Facts

Herchel's Garnet Star's Alternative Names

Mu Cephei (Mu. Cep) 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 HR8316. HIP107259 is the reference name for the star in the Hipparcos Star Catalogue. The Id of the star in the Henry Draper catalogue is HD206936.

Herchel's Garnet Star has alternative name(s) :- Erakis, mu. Cep.

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+58 2316.

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

Location of Herchel's Garnet Star

The location of the supergiant 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 Herchel's Garnet Star, the location is 21h 43m 30.45 and +58° 46` 48.2 .

Radial Velocity and Proper Motion of Herchel's Garnet Star

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 -3.51 ± 0.14 miliarcseconds/year towards the north and 5.36 ± 0.20 miliarcseconds/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 23.00 km/s with an error of about 0.58 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, Radius) of Herchel's Garnet Star

Herchel's Garnet Star Colour and Temperature

Herchel's Garnet Star has a spectral type of M2Ia. This means the star is a red supergiant star. The star has a B-V Colour Index of 2.24 which means the star's temperature has been calculated using information from Morgans @ Uni.edu at being 465 Kelvin.

Herchel's Garnet Star Radius

Herchel's Garnet Star has been calculated as 1,260.00 times bigger than the Sun.The Sun's radius is 695,800km, therefore the star's radius is an estimated 876,708,000.00.km. If you need the diameter of the star, you just need to multiple the radius by 2. The star's Iron Abundance is 0.05 with an error value of 9.99 Fe/H with the Sun has a value of 1 to put it into context.

Herchel's Garnet Star Apparent and Absolute Magnitudes

Herchel's Garnet Star has an apparent magnitude of 4.23 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 -6.81 If you used the 2007 Parallax value, you would get an absolute magnitude of -7.07. 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 Herchel's Garnet Star

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 0.62 which gave the calculated distance to Herchel's Garnet Star as 5260.70 light years away from Earth or 1612.90 parsecs. It would take a spaceship travelling at the speed of light, 5260.70 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 0.55 which put Herchel's Garnet Star at a distance of 5930.24 light years or 1818.18 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 375,023,932.22 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.

Variable Type of Herchel's Garnet Star

The star is a pulsating Semiregular late- (M 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. Herchel's Garnet Star brightness ranges from a magnitude of 4.142 to a magnitude of 3.622 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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Additional Herchel's Garnet Star Facts and Figures

Visual Facts


Primary / Proper / Traditional NameHerchel's Garnet Star
Alternative NamesMu Cephei, Mu. Cep, Erakis, HD 206936, HIP 107259, HR 8316, BD+58 2316, mu. Cep
Spectral TypeM2Ia
Constellation's Main StarNo
Multiple Star SystemYes
Star Type very luminous Supergiant Star
ColourRed
GalaxyMilky Way
ConstellationCepheus
Absolute Magnitude -6.81 / -7.07
Visual / Apparent Magnitude4.23
Naked Eye VisibleYes - Magnitudes
Right Ascension (R.A.)21h 43m 30.45
Declination (Dec.)+58° 46` 48.2
Galactic Latitude4.31 degrees
Galactic Longitude100.60 degrees
1997 Distance from Earth0.62 Parallax (milliarcseconds)
 5260.70 Light Years
 1612.90 Parsecs
2007 Distance from Earth0.55 Parallax (milliarcseconds)
 5930.24 Light Years
 1818.18 Parsecs
 375,023,932.22 Astronomical Units
Proper Motion Dec.-3.51 ± 0.14 milliarcseconds/year
Proper Motion RA.5.36 ± 0.20 milliarcseconds/year
B-V Index2.24
Radial Velocity23.00 ± 0.58 km/s
Iron Abundance0.05 ± 9.99 Fe/H

Companions (Multi-Star and Exoplanets) Facts


Exoplanet CountNone/Unaware

Variable Star Details


Variable Star ClassPulsating
Variable Star TypeSemiregular late- (M
Mean Variability Period in Days0.469
Variable Magnitude Range (Brighter - Dimmer)3.622 - 4.142

Estimated Calculated Facts


Radius (x the Sun)1,260.00 - 1,650.00
Effective Temperature465 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
206936+58 2316.0A-1.000000.00000M1Red
B12.300001878
C12.700001878

Location of Herchel's Garnet Star in Cepheus


Herchel's Garnet Star Location in Cepheus

The map was generated using Night Vision, an awesome free application by Brian Simpson.

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Comments and Questions

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LennyTuesday, 25th April 2017 8:24:10 PM
Such mind numbingly large distance and size.
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