This concept encompasses any star whose brightness, seen from the Earth is not constant. They can be stars whose light emission actually fluctuates - intrinsexas-, or stars whose light is interrupted in their path towards the Earth, by another star or a cloud of interstellar dust, extrinsic variable calls.
Changes in light intensity in the intrinsic variables is due to pulsations in the size of the Star (pulsing variables) or to interactions between the components of a double star. Some other intrinsic variables do not fit into any of these two categories.
The only frequent type of extrinsic variable is the "binary eclipsante" call. It's a double star consisting of two upcoming stars who regularly spend one ahead of the other. ALGOL is the most famous example. The binary eclipsantes constitute nearly 20% of known variable stars.
Variable końcaThe końca are oriented couples so, periodically, are eclipsed one to another. Probably the best-known examples are the variable końca, whose periodic pulse indicacan its brightness, therefore constitute an important reference for the measurement of distances in space.
Their pulsation periods vary between one day and about four months, and their brightness variations can be between 50 and 600% between the maximum and the minimum. Its name comes from its prototype or representative star, Delta Cefei.
The relationship between average brightness and the pulsation period was discovered in 1912 by Henrietta S. Leavitt, and is known as periodo-luminosidad. Leavitt found that the brightness of a cefeida increases in proportion to its pulse period.
Thus, astronomers can determine the intrinsic luminosity of a cefeida simply by measuring the pulsation period. The apparent brightness of a star in the sky depends on its distance from the Earth; Comparing this luminosity with brightness intrinsic distance which is can be determined. Thus, the końca can be used as indicators of distances both inside and outside of the milky way.
There are two types of końca. The most common are called classic końca and others, old and weak, are known as W Virginis star. The two types have different relationships period - luminosity.
Translation for educational purposes authorized by: Astronomía: Tierra, Sistema Solar y Universo