The first illustration here shows a Cepheid variable star. Cepheid variables actually change in brightness and are true variable stars. These stars have a layer of ionized hydrogen in their atmospheres that traps photons trying to escape. As these photons build up they heat the layer of hydrogen and it expands enough to become transparent. When this happens, photons can pass through the hydrogen layer and the star brightens. The hydrogen layer cools again and shrinks and becomes opaque to photons once more. Then the process begins again. This takes place over a period of hours to months. Long period variable stars (LPVs) operate in much the same way but the process takes months to years in these larger, cooler stars.

The cataclysmic variables are the exciting ones. The most extreme example is shown first- the supernova. A supernova occurs when a star runs out of fuel in its core, collapses into itself and rebounds in a tremendous explosion. For a short while, a supernova can outshine an entire galaxy of stars. But the variation only happens once.

The recurrent nova, or symbiotic star, occurs in a binary star system where a tiny dense white dwarf pulls material from a much larger companion star. As the gas the dwarf pulls from the companion builds up on its surface, the pressure and heat increase until an explosion occurs creating a huge burst of light and a sphere of gas that explodes outward away from the star. After the dust settles, the process begins again.