Space telescopes

by Chris Woodford. Last updated: May 20, 2011.

Light is the energy that lets us see, but it's not the only kind of energy objects hurl toward us. Point a telescope at the night sky and you'll see the light given off by distant stars, but you won't see all the other kinds of electromagnetic radiation—a vast amount of valuable information—they're sending our way. Ordinary, optical telescopes have told us most of what we know about the Universe. But because Earth's atmosphere scatters or distorts much of the other radiation given off by distant objects, telescopes stuck on the ground can answer only a fraction of our questions about space. The only real way to study the Universe is with a space telescope mounted on a satellite outside Earth's atmosphere. And there are plenty to choose from!

Photo: Redeployment of the Hubble Space Telescope (HST). Picture courtesy of Great Images in NASA. Telescopes like this, operating outside Earth's atmosphere, promise to tell us far more about the universe than we could ever learn from the ground.

How telescopes work

All telescopes work by collecting electromagnetic radiation (such as light, infrared, microwaves,or X-rays) given off by distant objects. Different kinds of space telescopes specialize in collecting different kinds of radiation. A satellite called the International Ultraviolet Explorer (IUE) launched in 1978 gained much information about objects such as supernovae (very bright exploding stars) by analyzing short-wavelength ultraviolet rays. These rays cannot be properly studied on Earth because they are scattered by the atmospheric ozone layer. High-energy gamma rays are given off during violent events in space. They have been studied by NASA's Compton Gamma-Ray Observatory, launched in 1991. At the other end of the electromagnetic spectrum, the Infrared Astronomical Satellite (IRAS) launched in 1983 was able to discover more than 350,000 new sources of infrared radiation, including six new comets. The $2 billion Hubble Space Telescope, launched in 1990, began a new era in space observation, sending back razor-sharp colored pictures of distant galaxies. It is so powerful that it can pick out objects 100 times fainter than the best telescopes on Earth.

Space telescopes have come a long way since the first Orbiting Solar Observatories (OSO) were launched in 1962. NASA's Next Generation Space Telescope (NGST), planned for a launch in 2007, will study infrared sources to find out more about how the first stars and galaxies in the Universe were formed.

Hubble Space Telescope

Photo of Hubble Space Telescope redeloyment by NASA

The 46 ft (14 m) Hubble Space Telescope is the largest such instrument ever built. It contains two cameras, one for photographing faint objects and the other for taking wide-angle shots. The other two instruments are spectroscopes, scientific instruments that can analyze the radiation given off by objects to work out their chemical composition. In addition, three fine guidance sensors help the Hubble to lock onto and track stars.

A fault in the Hubble's 8 ft (2.4 m) primary mirror was corrected by additional mirrors and lenses installed by Space Shuttle astronauts in 1993.

New guidance sensors and gyroscopes installed by a Space Shuttle mission in December 1999 ensure the telescope can lock onto and track objects with high precision.

Photo: The Hubble Space Telescope (HST).Picture courtesy of Great Images in NASA

Types of telescopes

Distant objects give off radiation in different bands of the electromagnetic spectrum. Astronomers can use a range of different telescopes to analyze the whole range of electromagnetic radiation, from long-wavelength radio waves to short-wavelength gamma rays. Here are some examples of the telescopes they use and the images they produce:

Radio waves Radio waves are picked up by dish-shaped radio telescopes. The largest telescope of this kind on Earth is the 305m (1000ft) Arecibo Observatory in Puerto Rico, operated by Cornell University. The dish pictured here is less than a quarter that size. It's the 70m (230ft) Canberra deep dish satellite in Australia. Photo by courtesy of Great Images in NASA.
Microwaves Cosmic microwaves cannot penetrate Earth's lower atmosphere, but they can be studied in space by satellites such as Cosmic Background Explorer (COBE). These images of the night sky were taken by COBE using different wavelengths of infrared light. Photo by courtesy of NASA Goddard Space Flight Center (NASA-GSFC).
Infrared Because water in the lower atmosphere absorbs infrared, instruments such as the Infrared Astronomical Satellite (IRAS) must study it in space. This is an image of the Andromeda Galaxy taken by IRAS. Photo by courtesy of NASA Ames Research Center (NASA-ARC).
Visible light Visible light from space is one thing we can easily see from Earth with any conventional, optical telescope. This one is the historic 66cm (26inch) refractor telescope at the U.S. Naval Observatory in Washington, D.C. However, Earth-bound telescopes like this can pick up only so much—hence the need for telescopes that travel into space. Photo by Seth Rossman courtesy of US Navy.	$The 26-inch refractor telescope at the U.S. Naval Observatory in Washington, D.C.$
Ultraviolet light Much ultraviolet light is absorbed by Earth's ozone layer, but satellites such as the International Ultraviolet Explorer (IUE) can study it from space. This ultraviolet image of Earth was taken from space in 1973. Photo by courtesy of NASA Glenn Research Center (NASA-GRC).
X rays Think of X rays and you probably think of broken bones—but they're whizzing round space too. Earth's atmosphere prevents these dangerous, high-energy rays from reaching telescopes on the ground, but space telescopes, such as the Roentgen Satellite (ROSAT), have been able to observe them in space. This image of the Sun was taken in December 2001 by the Soft X ray Telescope (SXT), an instrument onboard the Yohkoh observatory spacecraft. Photo by courtesy of NASA Goddard Space Flight Center (NASA-GSFC).
Gamma rays Most gamma rays are blocked out by Earth's atmosphere, but they can be studied in space by instruments such as the Compton Gamma-Ray Observatory (shown here whizzing over Baja California, Mexico in 1991, photographed from the Space Shuttle that launched it). It was named for US physicist Arthur Holly Compton (1892–1962), one of the first scientists to study cosmic rays. Photo by courtesy of NASA Johnson Space Center (NASA-JSC).