Not all stars in the night sky are equally bright. Most of these stars are stars that change their brightness periodically. Such stars are called variable stars. A star like this was first identified in 1912 by an American astronomer, Henrietta Swanlevity.
Scientists were convinced that variable stars exist in the universe after this scientist identified the star Delta Sepi in the Cepus constellation as a variable star. Further investigations of the star showed that it changes magnitude from 4.1 to 5.2 every 5.37 days. But Edwin P. Habil's further investigation of the star showed that it averaged 4.1 magnitude changes every 2 days. Between 500 and 600 such Delta Sepi stars have been identified so far. Hence, such stars are called sepide variable stars.
Apart from this, there are several types of variable stars. The changes in brightness of these variable stars over time can be observed and their light cycle can be obtained. Studying this light cycle can reveal more information about variable stars.
This eclipsing variable star, whose brightness decreases from magnitude 2.2 to 3.5 every 2.87 days, is a star called Algol or Beta Persi in the constellation Perseus. This can be observed with the naked eye. It is 82 light years away from Earth.
This long-period variable star in the constellation Citus is called Mira, or Omicron Ceti. The magnitude changes from 2.0 to 10.1 once every 331 days. This long periodic variable star was identified by the scientist De Pedricus in 1596. Long period variable stars of this type are common throughout the universe.
Stars that change their brightness from time to time are called irregular variable stars. This irregular variable star in the constellation Corona Borealis varies erratically from magnitude 2.0 to 15. The variable star Lambdatori, located in Taurus, belongs to the type of eclipsing double variable star. Its period is 3.953 days and changes magnitude from 3.4 to 3.9 in approximately 4 dayUs.
