Setting a Date 
Astronomers made an announcement a couple of months ago that sounded astonishing: The universe is a hundred million years older than previously thought — 13.8 billion years. What’s truly astonishing, though, is that the new age completely agrees with the older one.
In the 1920s, Edwin Hubble discovered that the universe is expanding. That implied that the universe had a beginning — that it had to expand from somewhere.
That beginning moment was dubbed the Big Bang. But figuring out when it took place depends on figuring out how fast the universe is expanding — a difficult task. By the 1990s, estimates placed the Big Bang at between 10 billion and 20 billion years ago.
Then in the ’90s, Hubble Space Telescope provided by far the best measurement of the expansion rate to date. Astronomers used that to calculate that the Big Bang took place 13.7 billion years ago.
But such measurements always have a bit of uncertainty. The Hubble observations had a range of about five percent either way. Later observations reduced the uncertainty, but there could still be an error of a few hundred million years.
The most recent measurement was made by Planck, a European spacecraft that observed the “afterglow” of the Big Bang. It gave an age of 13.8 billion years. But that’s well within the margin of error of the Hubble work. So the new observations confirm that astronomers have a solid idea of when the Big Bang took place — give or take a hundred million years or so.
Script by Damond Benningfield, Copyright 2013