The variety seen in double-star systems is nearly as rich as the galaxy’s stellar population as a whole. These pairs can differ significantly in mass, with, say, a mid-sized yellow star like our Sun locked in an orbital embrace with a far smaller, cooler red dwarf. Some binary partners evolve rapidly into red giant or supergiant stars, while their small companions remain stable. Binary systems also can host orbiting planets that have two stars in their skies, as on the fictional Tatooine in the Star Wars movies. And from our viewpoint on Earth, some binary stars stage their own eclipses. Eclipses are scientifically valuable because observing changes in light as one star passes in front of the other can reveal their masses, diameters, precise orbits, and even compositions. Pairs of neutron stars can spiral together and collide, producing some of the universe’s heavy elements, like gold, platinum, and iodine.