High above the Earth’s atmosphere, space
observatories such as the HUBBLE SPACE TELESCOPE can view the
Universe much more clearly than observatories on the ground. They can also pick
up different, invisible forms of radiation that the atmosphere absorbs, such as
gamma rays, X-rays, ultraviolet rays, and infrared rays. By looking at these
different wavelengths, astronomers can better understand how the Universe
works.
Gamma rays have
the shortest wavelengths and the most energy. They are produced by some of the
most violent events in the Universe, such as colliding galaxies.
High-energy X-rays are also emitted when violent events occur in
the Universe. They carry more energy than visible light and have longer
wavelengths than gamma rays. Here they are being emitted by the scattered
debris from a supernova explosion.
This ultraviolet image of the Sun reveals different temperatures
in the corona. Ultraviolet rays also have more energy than visible light, but
less than X-rays. They come from very hot objects, such as the Sun. These are
the rays that can burn the skin.
Infrared
rays have longer wavelengths than visible light. On Earth they are felt as
heat, and are also known as heat rays. In space they penetrate interstellar
dust and reveal what is behind it.
Radio
waves have the longest wavelengths and the lowest energy. In space they are
emitted from stars, galaxies, and gas clouds. Most can be picked up by
ground-based radio telescopes.
COMPTON GAMMA RAY OBSERVATORY
When it was launched in 1991, the Compton Gamma Ray Observatory was
the biggest space observatory ever. It mapped hundreds of gamma ray sources and
recorded more than 2,500 gamma ray bursts, signs of the most violent happenings
in the Universe.
CHANDRA X-RAY OBSERVATORY
The 13.7-m (45-ft) long Chandra X-ray Observatory is the
world’s most powerful X-ray telescope. In 1999, it was deployed from the
Space Shuttle and then boosted into a highly elliptical orbit that took it
140,000 km (87,000 miles) above Earth.
Since 1995, the Solar and Heliospheric Observatory (SOHO) has kept
watch on the Sun at ultraviolet and visible light wavelengths. It is located in
solar orbit 1.5 million km (930,000 miles) from Earth. SOHO investigates the
Sun’s surface, its interior, and its outer atmosphere, the corona.
Launched in 2003, the Spitzer Space Telescope is the largest
infrared telescope in space. It observes the Universe at invisible, infrared
wavelengths. The Spitzer looks at the cooler objects in space, such as small,
dim stars, extrasolar planets (planets round other stars), and giant clouds
between the stars. To make it ultrasensitive, its instruments are cooled by
liquid helium to around -273°C (-459°F).
Some of the most stunning images ever obtained of our
Universe have been sent back by the Hubble Space Telescope (HST). It works in
mainly visible light, but can also take infrared images. It was launched in
1990 from the space shuttle Discovery, and since then has been serviced and
updated four times by shuttle astronauts.
