Hubble - greatest discoveries
Age and size of the Universe:
How Hubble has calculated the age of the cosmos and discovered the Universe is expanding at an ever faster rate
The top ranked scientific justification for building Hubble was to determine the size and age of the Universe through observations of Cepheid variables. The periodic brightness variations of these stars depends on physical properties of the stars such as their mass and true brightness. This means that astronomers, just by looking at the variability of their light, can find out about the Cepheids' physical nature, which then can be used to determine their distance.
Astronomers have used Hubble to observe Cepheids with extraordinary results. The Cepheids have then been used as stepping-stones to make distance measurements for supernovae, which have, in turn, given a measure for the scale of the Universe. Today we know the age of the Universe to a much higher precision than before Hubble: around 13.7 billion years.
The expansion of the Universe
Another purposes of Hubble was to determine the rate of expansion of the Universe, known as the Hubble Constant. After eight years of Cepheid observations this work was concluded by finding that the expansion increases with 70 km/second for every 3.26 million light-years you look further out into space.
For many years cosmologists have discussed whether the expansion of the Universe would stop in some distant future or continue ever more slowly. The observations of distant supernovae made by Hubble indicate that the expansion is nowhere near slowing down. In fact, due to some mysterious property of space itself, called dark energy, the expansion is accelerating. This surprising conclusion came from combined measurements of remote supernovae with most of the world's top-class telescopes, including Hubble.
The discovery of the accelerating expansion of the Universe led to three astronomers, Saul Perlmutter, Adam Riess and Brian Schmidt, being awarded the 2011 Nobel Prize in Physics.
This is one of nine articles highlighting some of the greatest discoveries made by the Hubble Space Telescope. Read more in the articles linked from the right-hand menu.