This fact is now known as Hubble's law, though the numerical factor Hubble found relating recessional velocity and distance was off by a factor of ten, due to not knowing at the time about different types of Cepheid variables.

Wilson, Hubble identified Cepheid variables ( a kind of star ; see also standard candle ) in several spiral nebulae, including the Andromeda Nebula and Triangulum.

Wilson telescope, Edwin Hubble was able to resolve the outer parts of some spiral nebulae as collections of individual stars and identified some Cepheid variables, thus allowing him to estimate the distance to the nebulae: they were far too distant to be part of the Milky Way.

However, in 1986, Caldwell and Coulson found that field Cepheid variables in the northeast portion of the LMC lie closer to the Milky Way than Cepheids in the southwest portion.

The distance to the LMC has been calculated using a variety of standard candles, with Cepheid variables being one of the most popular.

Recently, the Cepheid absolute luminosity has been re-calibrated using Cepheid variables in the galaxy NGC 4258 that cover a range of metallicities.

On September 10, 1784 Edward Pigott detected the variability of Eta Aquilae, the first known representative of the class of Cepheid variables.

Observations of Cepheid variables are very important for determining distances to galaxies within the Local Group and beyond.

Light curves can be periodic, as in the case of eclipsing binaries, Cepheid variables, other periodic variables, and transiting extrasolar planets, or aperiodic, like the light curve of a nova, a cataclysmic variable star, a supernova or a microlensing event.

On September 10, 1784, Edward Pigott detected the variability of Eta Aquilae, the first known representative of the class of Classical Cepheid variables.

In 1924, Edwin Hubble established the distance to Classical Cepheid variables in the Andromeda Galaxy, and showed that the variables were not members of the Milky Way.

Hence, once the distance to the SMC was known with greater accuracy, Cepheid variables could be used as a standard candle for measuring the distances to other galaxies.

An example of this is the instability strip, a region of the H-R diagram that includes Delta Scuti, RR Lyrae and Cepheid variables.

In 1926, Edwin Hubble observed Cepheid variables in several spiral nebulae, including the Andromeda Galaxy, proving that they are, in fact, entire galaxies outside our own.

There are, for example, 273 Cepheid variables, 186 RR Lyr variables, 108 Delta Scuti variables, and 917 eclipsing binary stars.

RR Lyrae stars pulse in a manner similar to Cepheid variables, so the mechanism for the pulsation is thought to be similar, but the nature and histories of these stars is thought to be rather different.

RR Lyrae stars are found at all galactic latitudes, as opposed to classical Cepheid variables, which are strongly associated with the galactic plane.

( In fact, Walter Baade's failure to find them in the Andromeda galaxy led him to suspect that the galaxy was much farther away than predicted, to reconsider the calibration of Cepheid variables, and to propose the concept of stellar populations.

RR Lyrae stars, sometimes referred to as " Cluster Variables ", are somewhat similar to Cepheid type variables and as such can be used as a tool to measure distances in outer space since the relation between their luminosities and periods are well known.

Many oscillators, including the human voice, a bowed violin string, or a Cepheid variable star, are more or less periodic, and so composed of harmonics.

Chief among the uncertainties tied to the Classical and Type II Cepheid distance scale are: the nature of the period-luminosity relation in various passbands, the impact of metallicity on both the zero-point and slope of those relations, and the effects of photometric contamination ( blending ) and a changing ( typically unknown ) extinction law on Cepheid distances.

Two variable stars are Theta Circini, an irregular variable ranging from apparent magnitude 5. 0 to 5. 4, and AX Circini, a Cepheid Variable which ranges from 5. 6 to 6. 19 over 5. 3 days.

The energy output of a star over its lifespan should only change very gradually ; variable stars such as Cepheid variables, for instance, are highly unlikely to support life.

The brightest stars in M56 are of 13th magnitude, while it contains only about a dozen known variable stars, such as V6 ( RV Tauri star ; period: 90 days ) or V1 ( Cepheid: 1. 510 days ); other variable stars are V2 ( irregular ) and V3 ( semiregular ).

In the Hertzsprung – Russell Diagram, Mirfak lies inside the region in which Cepheid variables are found.

Edwin Hubble discovers a Cepheid variable star in the " Andromeda Nebula " and proves that Andromeda and other nebulas are galaxies far beyond our own.

Throughout their lifetime Delta Scuti stars exhibit pulsation when they are situated on the classical Cepheid instability strip.

These stars should not be confused with Cepheid variables, which are named after Delta Cephei.

In 1913 he determined the distances to several Cepheid variable stars by statistical parallax, and was thus able to calibrate the relationship discovered by Henrietta Leavitt between Cepheid period and luminosity.

In 1929, Hubble and Milton L. Humason formulated what is now known as Hubble's Law by combining Cepheid distances to several galaxies with Vesto Slipher's measurements of the speed at which those galaxies recede from us.

In 1908, the results of her study were published, which showed that a type of variable star called a " cluster variable ", later called a Cepheid variable after the prototype star Delta Cephei, showed a definite relationship between the variability period and the star's luminosity.

To this end, a standard candle measurement for Cepheid variables was discovered by Henrietta Swan Leavitt in 1908 which would provide Edwin Hubble with the rung on the cosmic distance ladder he would need to determine the distance to spiral nebula.

The speed at which he calculated the nebulae to rotate would, if Hubble were correct as to their extragalactic nature, have had their Cepheid stars moving at speeds faster than that of light.

By using the HARPS instrument, astronomers detected for the first time a double star where a pulsating Cepheid variable and another star pass in front of one another, which allows to measure the mass of the Cepheid.

Allan Sandage detected Cepheid variables in NGC 2403 using the Hale telescope, giving it the distinction of being the first galaxy beyond our local group within which a Cepheid was discovered.

Indeed, on the Hertzsprung – Russell diagram, Gamma Cygni lies close to the instability strip and its spectrum is markedly like that of a Cepheid variable.

In the 1950s, Walter Baade discovered that the nearby Cepheid variables used to calibrate the standard candle were of a different type than the ones used to measure distances to nearby galaxies.

This star is a Classical Cepheid variable that undergoes regular, periodic variation in luminosity because of radial pulsations.

The strong direct relationship between a Cepheid variable's luminosity and pulsation period secures for Cepheids their status as important standard candles for establishing the Galactic and extragalactic distance scales.

Initial studies of Cepheid variable distances were complicated by the inadvertent admixture of classical Cepheids and Type II Cepheids.

* 1952 — Walter Baade distinguishes between Cepheid I and Cepheid II variable stars

The nearby Cepheid variables were population I stars with much higher metal content than the distant population II stars.