Twenty One years of Hubble

Today marks the 21st anniversary of the launch of the Hubble Space Telescope and in order to celebrate, NASA have released a new image showing the interaction of spiral galaxy UGC 1810 with its companion UGC 1813.

The success of the Hubble Space Telescope took decades of persistence and hard work. German physicist Hermann Oberth was the first to consider a space based telescope in 1923 and, in 1946, American astronomer Lyman Spitzer discussed the two main advantages to Oberth's idea. Firstly, a space based telescope would have a much greater resolution than an equivalently sized ground based telescope. The stars appear to twinkle because their light changes velocity as it moves through air which varies in velocity and pressure, this problem is known as seeing. The best ground based telescopes are placed at high altitudes in order to minimise the amount of air that the light has to travel through. A space based telescope would not face this problem and would therefore be able to observe fainter, older, objects.

Spitzer also argued that a space based telescope would be able to observe objects at a greater range of wavelengths. Ground based telescopes cannot easily observe infrared or ultraviolet light because they are absorbed by the atmosphere. A final advantage of a space based telescope is that it does not suffer from as much light pollution as a ground based one.

Spitzer continued to campaign for a space based telescope and, in 1965, he was appointed to head a committee that would define the scientific objectives of such a mission. In 1970, NASA began to lobby Congress for funding and, after a nationwide campaign by astronomers, the Senate finally agreed to provide half the requested amount. The European Space Agency provided extra funding as well as staff, instruments and Solar cells. In return, they were promised 15% of the observing time. In 1978, they began designing the telescope which was due to launch in 1983.

That year, the telescope was named the Hubble Space Telescope after American astronomer Edwin Hubble. Hubble was the first to show that the universe is expanding and the expansion rate of the universe is known as Hubble's constant. One of the main objectives for the Hubble Space Telescope was to accurately determine Hubble's constant which could be used to calculate the age of the universe.

A number of technical problems meant that the launch date was delayed until October 1986. Tragically, the Challenger disaster occurred in January of that year. Seven people were killed including Christa McAuliffe, a teacher from New Hampshire, and shuttle missions were suspended until 1988. The launch date was finally set for 1990, when, on April 24th, the telescope was transported into orbit by the Space Shuttle Discovery.

Over all this time, the cost of the telescope had inflated from its original estimate of 400 million dollars to over 2.5 billion dollars. The telescope was too sensitive to be stored in normal atmospheric conditions and it cost about 6 million dollars a month to maintain on Earth.

Within weeks of the launch it became apparent that images of faint objects were suffering from spherical aberration. This occurs when the lens does not focus properly and the primary mirror was calculated to be about 2200 nanometers too flat (a nanometer is a millionth of a millimeter).

Hubble was designed to be serviced by astronauts but it would be impossible to replace the whole mirror whilst in orbit and so optical components had to be added to counter the effect. These were installed by seven astronauts over a period of ten days in 1993. Four service missions have since been conducted, the final one in 2009.

The Hubble Space Telescope has been responsible for thousands of scientific papers and it has been used to make a number of important discoveries. Anyone can apply for telescope time, regardless of their nationality, and time has been rewarded to thirteen amateur astronomers since its launch.

In 1997, the Hubble Space Telescope was used to show that most galaxies contain supermassive black holes at their centre and, two years later, it was used to determine Hubble's constant with 10% accuracy. The age of the universe was calculated to be between 9 and 14 billion years. This value was later refined by the Wilkinson Microwave Anisotropy Probe, which was launched in 2001. The same year that the Hubble Space Telescope helped confirm the existence of dark energy, which is accelerating the expansion of the universe.

In 2005, the Hubble Space Telescope was used to help determine how planets form by observing them in phases that had never been seen before. Three years later, it was used to make the first detection of an organic molecule in the atmosphere of an extra-solar planet, it was also used to confirm that the planet contained water.

The Hubble Space Telescope is still constantly being used to make new discoveries, only last week NASA announced that it had observed galaxies that formed 200 million years after the big bang, the oldest that have ever been recorded.

The Hubble Space Telescope has provided some of the most beautiful and iconic images of the universe, including two below. The first shows a star forming region in the Large Magellanic Cloud, the third closest galaxy to the Milky Way. The second shows the Boomerang Nebula which is the coldest place ever to be observed in the universe.