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Created page with "{{Night Sky | image = | designation =Garnet's Star<br/>HD 206936<br/>Mu. Cep | rightascension =21<sup>h</sup> 43<sup>m</sup> 30.4611<sup>s</sup><ref name=simbad..."
{{Night Sky
| image =
| designation =Garnet's Star<br/>HD 206936<br/>Mu. Cep
| rightascension =21<sup>h</sup> 43<sup>m</sup> 30.4611<sup>s</sup><ref name=simbad>{{cite web|url=http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=mu.+Cephei&submit=SIMBAD+search|title=Mu Cephei|accessdate=December 28, 2019|work=Simbad Astronomical Database|publisher=simbad.u-strasbg.fr}}</ref><ref name=hip>
{{cite journal
|last1=van Leeuwen |first1=Floor
|display-authors=3
|title=Validation of the new Hipparcos reduction
|journal=Astronomy and Astrophysics
|volume=474
|issue=2|page=653-664|date=2007
|doi=10.1051/0004-6361:20078357
|bibcode=2007A&A...474..653V
|ref=harv
}} {{arXiv|0708.1752}}</ref>
| declination =+58° 46′ 48.1602″<ref name=simbad/><ref name=hip/>
| distance =5,930.24 ly<ref name=universeguide>{{cite web|url=https://www.universeguide.com/star/garnetstar|title=Herchel's Garnet Star (Mu Cephei) Star Facts|accessdate=December 28, 2019|publisher=universeguide.com|date=February 12, 2017}}</ref>
| constellation =Cepheus
| type =Supergiant{{!}}Supergiant star
| dimensions =
| magnitude =Apparent mag: +4.23<ref name=universeguide/><br/>Absolute Mag: -6.81 / -7.07<ref name=universeguide/>
| redshift =
| radvelocity =23.00 ± 0.58 km/s<ref name=simbad/><ref>
{{cite journal
|last1=Mermilliod |first1=J. C.
|last2=Mayor |first2=M.
|last3=Udry |first3=S.
|display-authors=3
|title=Red giants in open clusters. XIV. Mean radial velocities for 1309 stars and 166 open clusters
|journal=Astronomy and Astrophysics
|volume=485
|issue=1|page=303-314|date=2008
|doi=10.1051/0004-6361:200809664
|bibcode=2008A&A...485..303M
|ref=harv
}}</ref>
| propmotion =RA: 5.36 mas/yr<ref name=simbad/><ref name=hip/><br/>Dec: -3.51 mas/yr<ref name=simbad/><ref name=hip/>
| parallax =0.55 ± 0.2 mas<ref name=simbad/><ref name=hip/>
}}
'''Mu Cephei''' (Mu. Cep, Erakis, HD 206936) is a [[Supergiant|supergiant star]] in the [[constellation]] of [[Cepheus]].<ref>{{cite web|url=https://www.aavso.org/vsots_mucep|title=Mu Cephei|accessdate=December 28, 2019|publisher=American Association of Variable Star Observers|April 13, 2010}}</ref> The star is known for being the reddest star visible to the unaided eye and was first observed by [[Johann Bayer]] who gave it the [[Bayer designation]] "Mu Cephei." The star can be seen high in the sky in summer and lies in the [[nebula]] IC 1396, making it an excellent target for astrophotographers. Although it can be seen with the unaided eye, it is better observed with [[binoculars]]. It is also a good target to observe in skies affected by [[light pollution]].<ref name=universetoday>{{cite web|url=https://www.universetoday.com/103491/seeing-red-hunting-herschels-garnet-star/|title=Seeing Red: Hunting Herschel’s Garnet Star|accessdate=December 28, 2019|publisher=universetoday|date=July 16, 2013|author=David Dickinson}}</ref>
==History==
Mu Cephei was first observed in 1600 by [[Johann Bayer]].<ref name=universeguide/> It was later observed by [[William Herschel]] in 1783, who noted the star possessed "a very fine deep garnet color." For this reason the star is sometimes called the "Garnet star" or "Herschel's Garnet star." The name is the for the star. John Russell Hind observed the star in 1848 and discovered that is was a [[variable star]], meaning its brightness changes over time.
==Properties and Structure==
The star is situated 5,930.24 [[light year]]s away, though some sources suggest it is closer at around only 2,400 ly.<ref name=universeguide/><ref name=constellation-guide>{{cite web|url=https://www.constellation-guide.com/constellation-list/cepheus-constellation/|title=Cepheus Constellation|accessdate=December 28, 2019|publisher=constellation-guide.com}}</ref> The star is a class M bright supergiant with a [[spectral class]] of M2Ia and one of the largest stars ever observed. The radius of Mu Cephei is 1,650 times greater than the [[Sun]], meaning it is roughly 7.7 times larger than the [[orbit]] of the [[Earth]] around the Sun.<ref name=constellation-guide/> Mu Cephei has a mass of 19 [[solar mass]]es and a [[luminosity]] of 600,000 solar luminosities.<ref name=universetoday/> This high luminosity means it is not only one of the brightest stars visible in the night sky but also the [[Milky Way|galaxy]]. The star is believed to have a surface temperature of 3,690±50 kelvin.<ref>{{cite web|url=https://freestarcharts.com/mu-cephei|title=Mu Cephei - Herschel's Garnet Star|accessdate=December 28, 2019|publisher=freestarcharts.com}}</ref>
The star deep red color is partly due to a cloud of interstellar dust located in between the star and Earth.<ref name=illinois>{{cite web|url=http://stars.astro.illinois.edu/sow/garnet.html|title=Garnet star|accessdate=December 28, 2019|work=Stars|author=Jim Kaler|date=September 20, 2017}}</ref> The dust absorbs bluer light more strongly than redder light, meaning there is light that reaches us on Earth than blue, and so the star appears red. If the dust was not present, the star would appear significantly brighter with an apparent magnitude of +1.97 rather than the observed +4.23.<ref name=illinois/> The red color is also due to the star itself emitting more light in the red region of the spectrum than the blue. A third factor is the Purkinje effect, an optical illusion where the longer someone looks a red star, the brighter it appears to become.
As a [[variable star]], its [[apparent magnitude]] varies from a minimum of +4.142 to a maximum of +3.622 and it varies in a semi-regular cycle.<ref name=universeguide/> Mu Cephei varies over a 755 day (2.5 year) cycle on average though other cycles ranging from 100 days to 12.8 years are known.<ref name=universetoday/> It is classified as a Semiregular late-M type variable star. It was the first of this type of variable star to be discovered.<ref name=constellation-guide/>
Mu Cephei is known to produce a strong [[stellar wind]] and is enclosed in a dusty shell that envelopes the star up to a distance of 15,000 [[Astronomical units]].<ref name=illinois/> This shell contributes to some of the reddening.
==References==
{{reflist}}
{{Stars}}
[[Category:Astronomy]]
[[Category:Stars]]
| image =
| designation =Garnet's Star<br/>HD 206936<br/>Mu. Cep
| rightascension =21<sup>h</sup> 43<sup>m</sup> 30.4611<sup>s</sup><ref name=simbad>{{cite web|url=http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=mu.+Cephei&submit=SIMBAD+search|title=Mu Cephei|accessdate=December 28, 2019|work=Simbad Astronomical Database|publisher=simbad.u-strasbg.fr}}</ref><ref name=hip>
{{cite journal
|last1=van Leeuwen |first1=Floor
|display-authors=3
|title=Validation of the new Hipparcos reduction
|journal=Astronomy and Astrophysics
|volume=474
|issue=2|page=653-664|date=2007
|doi=10.1051/0004-6361:20078357
|bibcode=2007A&A...474..653V
|ref=harv
}} {{arXiv|0708.1752}}</ref>
| declination =+58° 46′ 48.1602″<ref name=simbad/><ref name=hip/>
| distance =5,930.24 ly<ref name=universeguide>{{cite web|url=https://www.universeguide.com/star/garnetstar|title=Herchel's Garnet Star (Mu Cephei) Star Facts|accessdate=December 28, 2019|publisher=universeguide.com|date=February 12, 2017}}</ref>
| constellation =Cepheus
| type =Supergiant{{!}}Supergiant star
| dimensions =
| magnitude =Apparent mag: +4.23<ref name=universeguide/><br/>Absolute Mag: -6.81 / -7.07<ref name=universeguide/>
| redshift =
| radvelocity =23.00 ± 0.58 km/s<ref name=simbad/><ref>
{{cite journal
|last1=Mermilliod |first1=J. C.
|last2=Mayor |first2=M.
|last3=Udry |first3=S.
|display-authors=3
|title=Red giants in open clusters. XIV. Mean radial velocities for 1309 stars and 166 open clusters
|journal=Astronomy and Astrophysics
|volume=485
|issue=1|page=303-314|date=2008
|doi=10.1051/0004-6361:200809664
|bibcode=2008A&A...485..303M
|ref=harv
}}</ref>
| propmotion =RA: 5.36 mas/yr<ref name=simbad/><ref name=hip/><br/>Dec: -3.51 mas/yr<ref name=simbad/><ref name=hip/>
| parallax =0.55 ± 0.2 mas<ref name=simbad/><ref name=hip/>
}}
'''Mu Cephei''' (Mu. Cep, Erakis, HD 206936) is a [[Supergiant|supergiant star]] in the [[constellation]] of [[Cepheus]].<ref>{{cite web|url=https://www.aavso.org/vsots_mucep|title=Mu Cephei|accessdate=December 28, 2019|publisher=American Association of Variable Star Observers|April 13, 2010}}</ref> The star is known for being the reddest star visible to the unaided eye and was first observed by [[Johann Bayer]] who gave it the [[Bayer designation]] "Mu Cephei." The star can be seen high in the sky in summer and lies in the [[nebula]] IC 1396, making it an excellent target for astrophotographers. Although it can be seen with the unaided eye, it is better observed with [[binoculars]]. It is also a good target to observe in skies affected by [[light pollution]].<ref name=universetoday>{{cite web|url=https://www.universetoday.com/103491/seeing-red-hunting-herschels-garnet-star/|title=Seeing Red: Hunting Herschel’s Garnet Star|accessdate=December 28, 2019|publisher=universetoday|date=July 16, 2013|author=David Dickinson}}</ref>
==History==
Mu Cephei was first observed in 1600 by [[Johann Bayer]].<ref name=universeguide/> It was later observed by [[William Herschel]] in 1783, who noted the star possessed "a very fine deep garnet color." For this reason the star is sometimes called the "Garnet star" or "Herschel's Garnet star." The name is the for the star. John Russell Hind observed the star in 1848 and discovered that is was a [[variable star]], meaning its brightness changes over time.
==Properties and Structure==
The star is situated 5,930.24 [[light year]]s away, though some sources suggest it is closer at around only 2,400 ly.<ref name=universeguide/><ref name=constellation-guide>{{cite web|url=https://www.constellation-guide.com/constellation-list/cepheus-constellation/|title=Cepheus Constellation|accessdate=December 28, 2019|publisher=constellation-guide.com}}</ref> The star is a class M bright supergiant with a [[spectral class]] of M2Ia and one of the largest stars ever observed. The radius of Mu Cephei is 1,650 times greater than the [[Sun]], meaning it is roughly 7.7 times larger than the [[orbit]] of the [[Earth]] around the Sun.<ref name=constellation-guide/> Mu Cephei has a mass of 19 [[solar mass]]es and a [[luminosity]] of 600,000 solar luminosities.<ref name=universetoday/> This high luminosity means it is not only one of the brightest stars visible in the night sky but also the [[Milky Way|galaxy]]. The star is believed to have a surface temperature of 3,690±50 kelvin.<ref>{{cite web|url=https://freestarcharts.com/mu-cephei|title=Mu Cephei - Herschel's Garnet Star|accessdate=December 28, 2019|publisher=freestarcharts.com}}</ref>
The star deep red color is partly due to a cloud of interstellar dust located in between the star and Earth.<ref name=illinois>{{cite web|url=http://stars.astro.illinois.edu/sow/garnet.html|title=Garnet star|accessdate=December 28, 2019|work=Stars|author=Jim Kaler|date=September 20, 2017}}</ref> The dust absorbs bluer light more strongly than redder light, meaning there is light that reaches us on Earth than blue, and so the star appears red. If the dust was not present, the star would appear significantly brighter with an apparent magnitude of +1.97 rather than the observed +4.23.<ref name=illinois/> The red color is also due to the star itself emitting more light in the red region of the spectrum than the blue. A third factor is the Purkinje effect, an optical illusion where the longer someone looks a red star, the brighter it appears to become.
As a [[variable star]], its [[apparent magnitude]] varies from a minimum of +4.142 to a maximum of +3.622 and it varies in a semi-regular cycle.<ref name=universeguide/> Mu Cephei varies over a 755 day (2.5 year) cycle on average though other cycles ranging from 100 days to 12.8 years are known.<ref name=universetoday/> It is classified as a Semiregular late-M type variable star. It was the first of this type of variable star to be discovered.<ref name=constellation-guide/>
Mu Cephei is known to produce a strong [[stellar wind]] and is enclosed in a dusty shell that envelopes the star up to a distance of 15,000 [[Astronomical units]].<ref name=illinois/> This shell contributes to some of the reddening.
==References==
{{reflist}}
{{Stars}}
[[Category:Astronomy]]
[[Category:Stars]]