Galaxy Ages

How do astronomers use look-back time to study the universe?

In a sense, look-back time is an imprecise measure because we can only guess how distant galaxies look today. But on the flip side, astronomers can use look-back time to study how the universe has aged and evolved since the distant past. That is because we directly observe how distant galaxies looked into the past—we do not need to rely on fossils or subjective writings, as biologists and historians might. It is as if we took a picture of a town or city many years ago and then compared it with another photograph taken recently to see how it has changed. With this tool, astronomers can figure out how the universe has evolved and changed going back to a time almost as early as the Big Bang, 13.7 billion years ago.


This is a web preview of the "The Handy Astronomy Answer Book" app. Many features only work on your mobile device. If you like what you see, we hope you will consider buying. Get the App