Intrinsic variable stars are those whose brightness varies cyclically, that is, it increases and decreases periodically. Your periods can last anywhere from hours to years. These stars have played a very important role in astrophysics, since they have made it possible to determine the distances between objects in the Universe. The graphs of its brightness as a function of time are of the sinusoidal type. Astronomical studies have made it possible to determine their periods, their average brightness and their variation, which is why it has been possible to obtain the functions that represent their brightness. One of the most visible stars is Delta Caphei, for which we have the function of its brightness expressed as:

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