A star that belongs to a class of yellow super-giant pulsating stars. These stars vary periodically in brightness, and the relationship between their periods and luminosities is useful in deriving distances to them.
A type of supergiant star that oscillates in brightness in a manner similar to the star 8 Cephei. The periods of Cepheid variables, which are between 1 and 100 days, are linked to the absolute magnitude of the stars by known relationships; this allows the distances to Cepheids to be found.
A variable star which, like the prototype, Delta Cephei, varies in brightness in a particular way. Cepheid variables which are intrinsically brighter take longer to vary than ones which are intrinsically fainter, making it easy to estimate their true brightness, and from that, their distance.
An important class of periodic pulsating variable star that obeys a period-luminosity relationship discovered by Henrietta Leavitt. Type I or classical Cepheids are giant luminous yellow stars with periods of 5 -10 days. Type II Cepheids or W Virginis stars are about teo magnitudes dimmer than Type Is for the same period and have periods of about 12 - 30 days. The longer the period of a Cepheid, the more intrinsically luminous it is. This allows them to be used as "standard candles" and are thus important distance indicators for the extragalactic distance scale.
A variable star whose period of variability is directly proportional to its mass. Cepheid variables are a valuable tool to astronomers. Measuring the period of a Cepheid variable allows one to calculate the star's mass and, therefore, intrinsic brightness. A comparison of the intrinsic and apparent brightnesses leads to an estimate of the star's distance. Cepheid variables provided the first concrete evidence that spiral nebulae are distant galaxies beyond the Milky Way.
A type of variable star that exhibits a regular pattern of changing brightness over time, and in which the period of the pattern is directly related to the star's intrinsic brightness. Cepheid variables are an indispensable tool for determining distances in modern astronomy.
Star whose luminosity varies in a characteristic way, with a rapid rise in brightness followed by a slower decline. The period of a Cepheid variable star is related to its luminosity, so a determination of this period can be used to obtain an estimate of the star's distance.
An unstable star whose brightness changes periodically. In 1912, Henrietta Leavitt discovered what is known as the Period-Luminosity Relationship for Cepheid variables, by which the period of the brightness change is related to the luminosity, and therefore the distance, of the star. An astronomer can record the changing brightness of a Cepheid variable and plot the brightness change over time to create a light curve for the star. The distance to the Cepheid variable is then obtained by measuring the period of the light curve.
An important type of variable star. Stars of this type have short periods, from a few days to a few weeks; these stars are perfectly regular. The period of a Cepheid depends on its absolute magnitude. So, when the period of variability is known, its absolute magnitude can be deduced. Comparing this to its apparent magnitude (how bright it is when seen from Earth) gives the distance. They are sometimes referred to as "standard candles" because of their usefulness in determining the distances of galaxies. They are named after the star Delta Cephei, which was the first one of this type of star to be discovered.
A Cepheid variable or Cepheid is a member of a particular class of variable stars, notable for a fairly tight correlation between their period of variability and absolute luminosity. The namesake and prototype of these variables is the star Delta Cephei, discovered to be variable by John Goodricke in 1784.