A white dwarf is the final stage in the life of a star like the Sun that slowly cools down by radiating light. Knowing how the white dwarf’s temperature changes with time (cooling), astronomers can deduce the age of the white dwarf. By observing lots of white dwarfs and calculating their temperatures, astronomers can estimate the age of our galaxy. Students learn about cooling curves by measuring the temperature decline in boiling water and extend those concepts to cooling white dwarfs.