This would mean that the universe was only half the size and age that Sandage believed—ten billion years. Matters took a further lurch into uncertainty when in 1994 a team from the Carnegie Observatories in California, using measures from the Hubble space telescope, suggested that the universe could be as little as eight billion years old—an age even they conceded was younger than some of the stars within the universe. In February 2003, a team from NASA and the Goddard Space Flight Center in Maryland, using a new, far-reaching type of satellite called the Wilkinson Microwave Anistropy Probe, announced with some confidence that the age of the universe is 13.7 billion years, give or take a hundred million years or so. There matters rest, at least for the moment.

You are of course entitled to wonder what is meant exactly by "a constant of 50" or "a constant of 100." The answer lies in astronomical units of measure. Except conversationally, astronomers don't use light-years. They use a distance called the parsec (a contraction of parallax and second), based on a universal measure called the stellar parallax and equivalent to 3.26 light-years. Really big measures, like the size of a universe, are measured in megaparsecs: a million parsecs. Thus when astronomers refer to a Hubble constant of 50, what they really mean is "50 kilometers per second per megaparsec."