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Variable star, even the stars are lunatic? A variable star is a star whose apparent brightness changes over time. They may show variations ranging from a few thousandths of a magnitude to twenty magnitudes in periods ranging from fractions of a second to years. The variation can be caused either by an actual change in the emitted light, either by a change in the quantity of radiation which reaches the Earth.
Many stars, maybe most of them, change brightness in time. The Sun is no exception: its brightness varies by 0.1% during its eleven-year cycle.
The first variable star to be recognized as such was Mira: in 1638 Johannes Holwarda noticed that it ranged its brightness with a period of 11 months. The latest edition of the General Catalogue of Variable Stars cataloged approximately 46,000 variable stars in our galaxy, about 10,000 belong to other galaxies and more than 10,000 suspected variables. Variable stars are generally analyzed using photometric techniques, spectrophotometric and spectroscopic. The measurements of their photometric changes can be used to plot the graph of the light curve, which shows the trend of the quantity of radiation emitted by the star in time. The amateur astronomers can make an important contribution to the study of variable stars, by comparing the brightness of a variable with that of other stars that are in the same telescopic field and have been recognized as non-variables. By estimating the variations in brightness over time, you can build the variable light curve. At first discovered variable stars in a Constellation, you are assigned letters from A to Z, for example, R Coronae Borealis. This nomenclature has been in place since Friedrich W. Argelander assigned to a yet unnamed letter variable star R, the first unused letter of Bayer nomenclature in its constellation.
This nomenclature has been in place since Friedrich W. Argelander assigned to a yet unnamed letter variable star R, the first unused letter of Bayer nomenclature in its constellation. Variable stars can be divided into two broad classes: the intrinsic variables and extrinsic variables. In the variability, intrinsic variables are caused by physical changes of the star. In the extrinsic variables variability, it is not caused by the star physical changes, but by other factors, such as eclipses or stellar rotation.
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