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From November 13, 2006.

You hear distances all the time in astronomy. This star is 10 light-years away; that galaxy is 50 million light-years away; that Big Bang over there happened 13.7 billion years ago. But how did astronomers actually figure out how far away everything is? It’s not a single measuring stick. Instead, astronomers have built up a series of overlapping measuring tools (yes, we’re calling supernovae and variable stars “tools”), which take us from right around the corner to very ends of the Universe. Get out your ruler… no, the bigger one… never mind… just listen.

 

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