RW Cephei (Supergiant Star) Star Facts

Facts

• RW Cephei is a very luminous Supergiant Star type star. RW Cephei is a G8IAVAR supergiant star based on the spectral type that was recorded in the Hipparcos star catalogue.
• RW Cephei is not part of the Cepheus constellation outline but is within the borders of the constellation.
• Based on the spectral type (G8Iavar) of the star, the star's colour is yellow .
• The star can be seen with the naked eye, that is, you don't need a telescope/binoculars to see it.
• Using the most recent figures given by the 2007 Hipparcos data, the star is 4026.71 light years away from Earth.

Location

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 RW Cephei, the location is 22h 23m 07.02 and +55° 57` 47.6 .

Radial Velocity and Proper Motion

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 -2.66 ± 0.29 milliarcseconds/year towards the north and -2.74 ± 0.36 milliarcseconds/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 -56.00000 km/s with an error of about 5.70 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 and Temperature

Based on the star's spectral type of G8Iavar , RW Cephei's colour and type is yellow supergiant star. Based on the spectral type, we can deduce that the surface temperature of the star is in the order of between 5,000 and 6,000K based on the notes from Harvard University. To put this in context, the temperature of our Sun is about 5,778 Kelvin as said by Google.

Radius

RW Cephei estimated radius has been calculated as being 3,865.72 times bigger than the Sun. The Sun's radius is 695,800km, therefore the star's radius is an estimated 2,689,769,264.59.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 5,691.66. The figure is derived at by using the formula from SDSS rather than peer reviewed papers. It has been known to produce widely incorrect figures.

Apparent (Brightness) and Absolute Magnitudes

RW Cephei has an apparent magnitude of 6.44, this is a measure of the brightness of the star as seen from Earth. Apparent Magnitude is also known as Visual Magnitude. If you used the 1997 Parallax value, you would get an absolute magnitude of -3.18 If you used the 2007 Parallax value, you would get an absolute magnitude of -4.02.

Absolute Magnitude is the apparent magnitude of the star from a distance of 10 parsecs or 32.6 light years. This assumes that there is nothing in between the object and the viewer such as dust clouds. To really compare the brightness of the star, it is best to use Absolute rather than Apparent Magnitude.

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 from Earth

Using the original Hipparcos data that was released in 1997, the parallax to the star was given as 1.19000 which gave the calculated distance to RW Cephei as 2740.87 light years away from Earth or 840.34 parsecs. If you want that in miles, it is about 16,112,547,926,597,761.14, based on 1 Ly = 5,878,625,373,183.61 miles.

In 2007, Hipparcos data was revised with a new parallax of 0.81000 which put RW Cephei at a distance of 4026.71 light years or 1234.57 parsecs. It should not be taken as though the star is moving closer or further away from Earth. It is purely that the distance was recalculated.

Using the 2007 distance, the star is roughly 254,646,567.45 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.

Alternative Names and Meanings

• HIP110504 is the reference name for the star in the Hipparcos Star Catalogue.
• The Id of the star in the Henry Draper catalogue is HD212466. The catalogue was started by the American doctor and has been expanded on over the years.
• The star is catalogued in the Tycho-2 star catalogue as TYC-3986-365-1. The catalogue lists 2 millions stars and its homepage is E.S.A.
• 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+55 2737.
• The two letters at the start identify that the star is a variable star. The letters are allocated as the next in the list up e.g. GH follow GG, all the way up to ZZ then a V and a number is the next in the order.

Travel Time

The time it will take to travel to this star is dependent on how fast you are going. U.G. has done some calculations as to how long it will take going at differing speeds. A note about the calculations, when I'm talking about years, I'm talking non-leap years only (365 days).

The New Horizons space probe is the fastest probe that we've sent into space at the time of writing. Its primary mission was to visit Pluto which at the time of launch (2006), Pluto was still a planet.

Mach 1 is the speed of sound, Mach 2 is twice the speed of sound. Corncorde before it was retired was the fastest commercial airline across the Atlantic and only one that could do Mach 2.

Variable Type

The star is a pulsating Slow Irregular 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. RW Cephei brightness ranges from a magnitude of 6.620 to a magnitude of 6.456 over its variable period. The smaller the magnitude, the brighter the star. Its variable/pulsating period lasts for 0.2 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.