The night sky, with its familiar patterns of stars cross our skies year after year, appears perfect, steady, peaceful, serene, and unchanging. However, the reality of the stars in our Universe are much different than this idealistic view.
Stars are a giant balls of gas in a delicate balancing act between the force of gravity trying to crush all the mass and the force of nuclear burning at the core of the startrying to blow it apart.
Throughout its life, there are sometimes battles fought between these two forces that ebb and flow, swelling and shrinking the star. This causes their light to vary.
Others light varies, not because of internal struggles, but of exterior interactions. Together, these two types of interactions create a group of stars known as Variable Stars. Every star has been and will be variable in its light output at one time or another. It is inevitable. If you could just live long enough you’d see every star is a variable star.