Today would have been Edwin Hubble's birthday. He was born 110 years ago on November 20th, 1889, and as a young man he excelled at boxing, going far enough to be offered a contest with the reigning heavyweight world champion of the day, Jack Johnson. Wisely declining this dangerous invitation, Hubble studied law and practised for some years before finally changing tack again to take a doctorate in astronomy.
In this profession he was eminently successful; he provides the eponym for both the Hubble telescope and Hubble constant.
Both have had their share of controversy. The Hubble space telescope became notorious shortly after its multimillion dollar launch in 1990; it was discovered to have a faulty mirror, which rendered it more or less completely useless.
But the defect was rectified in 1993 by means of the longest and most expensive space walk yet undertaken, and since then Hubble has produced a stream of images that are unparalleled in scientific history.
The squabble over the Hubble constant has been longer. In 1929 Edwin Hubble noticed that with few exceptions the galaxies of the universe were all retreating from the Earth, and that the more distant galaxies were receding faster than the nearer ones.
From his observations, Hubble proposed a precise relationship - that the speed of recession is directly proportional to the distance of a galaxy from Earth, the speed and distance being related by a number that we now call Hubble's constant. An accurate assessment of the Hubble constant would allow cosmologists to estimate the age of the universe by extrapolating backwards to the "Big Bang".
But the value of the constant has proved to be extremely variable; indeed for 60 years it was one of the great uncertainties of modern science.
Over the years it became generally accepted that the constant was somewhere between 50 and 100 kilometres per second per megaparsecond. But where you pitch it within those limits has profound implications for the age of the universe.
If the constant is small, the universe would have taken a very long time to reach its present state; if large, the cosmos is relatively young. The range, depending on which value of the Hubble constant may appeal to you, is between eight and 15 billion years old.
But it looks as if the Hubble telescope may have cleared up the mystery of the Hubble constant. Recent estimates, based on measurements of an accuracy that only this telescope give, and arrived at by several methodologies, all agree that the value is around 70 - which places the age of the universe at about 12 billion years.