Some stars look single to the naked eye but really are two stars orbiting each other.
These binary systems form when giant clouds of gas and dust collapse gravitationally into two condensations instead of one. Sometimes, just by chance, the orbital plane is nearly along our line of sight to the stars. When this happens we can observe eclipses as the stars pass in front of one another during orbital motion. Here are light curves for some eclipsing binaries measured at Winfree Observatory. The larger star of the pair has 99 percent of our Sun's mass, has 1.14 times the diameter of our Sun, and puts out 1.45 times more power than our Sun.