Flexi Says: Astronomers estimate the age of the universe using different lines of evidence. One is simply by looking for the oldest stars and galaxies. The farther away an object is in space, the longer the light takes to reach Earth. So, studying distant objects is like looking back in time. Determining the age of the most distant objects gives astronomers some limits for the age of the universe. Another line of evidence is the rate of expansion of the universe. By analyzing the shifting of light that comes from distant galaxies, astronomers have determined that all of the galaxies are moving apart from each other as the space between them expands. Astronomers can estimate the rate of expansion by studying light from many galaxies. Then they use this rate to extrapolate back to the Big Bang which began the universe.