There is hardly any other scientific instrument in the world that can match the Hubble telescope in fame. In the four centuries since the invention of the first telescope, Hubble and its sister telescopes in space have revolutionised the way we understand the cosmos.
Hubble has been orbiting the earth for 20 years this month. “It has achieved much more than anyone thought possible,” says Robert Fosbury, the head of the European Space Agency’s team that coordinates with NASA on the Hubble telescope. “Hubble has given us access to completely new areas of astronomy.” That growth in knowledge is illustrated by the work done by Hubble on distant worlds, known as extrasolar planets, such as stars. “When Hubble launched no one had discovered an extrasolar planet,” says Fosbury. Today, Hubble is even examining the chemical make-up of the atmospheres of those planets. Thanks to Hubble, astronomers were able to prove the existence of organic molecules outside our solar system and in this way the telescope is on the trail of possible extraterrestrial life.
Hubble’s big advantage is that it is stationed outside the earth’s atmosphere and has a clear view of space. Astronomers were able to identify individual stars in distant galaxies for the first time. Orbiting telescopes are also able to see wavelengths of light, such as infrared, which are absorbed by the atmosphere.
Hubble has created a huge body of work in its lifetime. It has taken approximately 600,000 images of about 30,000 objects in space since 1990. Every month it sends 80 gigabytes of information back to earth - the equivalent of about 80 large encyclopaedias. The cost of the project to NASA and the European Space Agency, which has a 15 per cent stake in Hubble, has been 10 billion dollars thus far.
The telescope has also helped to explain how stars and planets are created, set the age of universe at approximately 13.7 billion years and has investigated the mysterious concept of dark energy, which is driving the universe’s expansion.
It has also delivered countless images that have enthralled the public. Hubble’s success is also the story of well coordinated publicity. “These images are often just as significant for the scientists as for the public,” says Fosbury. The type of image can help the scientists maintain an overall view. The brilliant colours the images come in are a combination of several individual exposures in different wavelengths.
In many cases, common features that are difficult to pin down in the single images often become immediately clear when viewed in combination with other exposures, according to Fosbury. “The colour images contain a lot of physics because the colours show us the properties of gases, stars and other materials.” But Hubble has not only made the universe more colourful, it has also made it larger. “When Hubble began operation the most distant objects that humans could see were about halfway to the origin’s of the universe,” says Fosbury. In what appeared to be empty areas of the heavens Hubble discovered thousands of galaxies at distances of billions of light years.
It has not managed to look back at the beginnings of the universe, “but it has taken us to the first few billion years. That has revolutionised cosmology,” says Fosbury. That goal has been the driving force behind the next generation of extraterrestrial observatory, the James Webb Space telescope, which is due to launch in 2014.
The story of the Hubble telescope goes back decades before it was sent into orbit around the earth. The first person to conceive the idea of an orbiting telescope was rocket pioneer Hermann Oberth (1894—1923). In 1977 the US congress approved a budget for a space observatory.
The project quickly received its name in honour of the American astronomer Edwin Hubble (1889—1953) who in the 1920s proved the universe was expanding and thus provided the foundation stone for the big bang theory. Then, on April 24 1990, the space shuttle Discovery transported Hubble into orbit around the earth.
The project hit a major setback two months after launch when Hubble’s 2.4—metre—wide primary mirror, which was lauded as the “flattest mirror in the world,” was shown to have been made in the wrong shape. That flaw meant the telescope was limited in the extent to which it could see objects.
After three years Hubble received corrective optics during the first service mission. Astronauts flew a further four times to Hubble leaving a practically new instrument behind them each time.
The last Hubble service mission was in May 1999 and no more are planned as NASA’s space shuttle fleet is due to be mothballed this year. How long Hubble will be able to function after that is not known. However, scientists are still eager to gather new images from the observatory. “Astronomers have applied for 10 times more observatory time than is available,” says Fosbury. “That’s a record.”