Astronomy   View all facts   Glossary   Help

physical object > natural object > celestial body > star > variable > periodic variable > Cepheid

Cepheid
subject			fact

Cepheid	has period 1 to 50 days
	has prototype delta Cephei
	has spectral type F star, G star and K star
	has definition A yellow supergiant that pulsates, alternately brightening and dimming. Cepheids allow astronomers to measure distances, because the longer a Cepheid's period of variation, the greater the Cepheid's mean intrinsic brightness. To determine a Cepheid's distance, all an astronomer has to do is measure the Cepheid's period; comparing the star's mean intrinsic brightness with the star's mean apparent brightness then yields the distance. Cepheids are so bright that we can see them in other galaxies, allowing us to establish distances to entire galaxies beyond the Milky Way.
	has definition One of a group of very luminous supergiant pulsating stars. The luminosities of a Cepheid is proportional to its period, but a different P-L relation applies to each type. No Cepheid is near enough for an accurate trigonometric parallax (Polaris is the nearest). Cepheids are useful distance indicators to about 3 Mpc.
	has definition A type of variable star whose period of variation is tightly related to its intrinsic luminosity.
	has definition A class of stars named after Delta Cephei which vary in brightness over a regular period of time (typically a few days). The period of change is directly related to the true, average brightness or luminosity of the star. Once the period is known the true brightness can be calculated and the distance estimated by observing the "apparent" brightness of the object as seen from Earth.
	has definition Strictly periodic variables with periods 1-50 days, of spectral types F, G and K.
	is a kind of periodic variable
variable	has name designated with R, S, T, U, V, W, X, Y, or Z and the genitive of the latin constellation name RR, RS, RT, RU, RV, RW, RX, RY, or RZ and the genitive of the latin constellation name when the single letter designations are exhausted AA...AZ, BB...BZ, etc. (omitting J), which ends with QQ...QZ and the genitive of the latin constellation namewhen the RR...RZ designations are exhausted V 335, V 336, etc., when the double letter designations are exhausted
	has observational problem some difficulty in distinguishing between various kinds
	has observable variation time scale within a period of decades
	has light curve
	has optical brightness variation 0.2 magnitudes or greater
	has amplitude
star	has star surface temperature
	has V magnitude
	has B magnitude
	has U magnitude
	has position on celestial sphere from the point of view of Earth
	has parallax from the point of view of Earth's orbit
	has proper motion
	has radiation at surface which is diffused out from the hotter core
	has energy source gravitational contraction and or fusion
	has energy production which takes place primarily within the core
	has surface density which depends on luminosity class
	has surface temperature greater than 1000 Kelvin
	has apparent magnitude
	has absolute magnitude
	has age
	has catalog star catalog
	has material hydrogen, helium
	has velocity determined from proper motion and radial velocity
	has mass greater than 0.08 the sun's mass
celestial body	has spectra
physical object	has location or center of gravity
	has angular momentum
	has momentum
	has temperature
	has volume
	has extent

Kinds of Cepheid :

• dwarf Cepheid (3 kinds, 15 facts) (delta Scuti star, ultrashort-period Cepheid) - Type I Cepheids ( <M_v> +4 to +2)., A group of pulsating variable stars with small variations in amplitude. They lie in the lower part of the Cepheid instability strip.
• Population I Cepheid (3 kinds, 34 facts) (classical Cepheid, young disk Cepheid) - A Cepheid which is about 4 times more luminous than Population II Cepheids, probably because of their higher metal content (although mass may also be a factor).
• Population II Cepheid (7 facts) (W Virginis star) - A bright yellow star that pulsates like a Cepheid but is older and fainter.

Next periodic variable: eclipsing binary    Up: periodic variable    Previous periodic variable: beta Cephei star