Telescopes
Telescopes help us see things that
are far away. They make distant objects look bigger. Using telescopes,
astronomers have discovered thousands of stars, planets, moons, and many other
extraordinary objects, such as black holes.
The most common type of telescope
is the optical telescope. This kind of telescope gathers light from distant
objects.
HOW DO OPTICAL TELESCOPES WORK?
Imagine having eyes as big as your
fist. You’d look funny, but more light would enter your eyes. You would be able
to see better. Telescopes bring extra light to our eyes. They effectively make
our eyes bigger. Distant objects appear larger when you look through a
telescope, and you can see more detail.
A refracting telescope is the
simplest type of optical telescope. It is made up of two lenses. These lenses
are similar to the lens in a magnifying glass. A reflecting telescope has a lens
and a dish-shaped mirror. The mirror collects and focuses (concentrates)
light.
A telescope’s eyepiece can be
replaced by a camera. Then the image from the telescope is recorded on film or
as a digital image.
GIGANTIC OPTICAL TELESCOPES
The bigger a telescope’s main
lens or mirror, the more light the telescope gathers. The more light the
telescope gathers, the more detail it shows, and the more distant the objects
that you can see through it.
Astronomers use huge telescopes
housed inside buildings called observatories. These telescopes have mirrors as
large as 26 feet (8 meters) across. They gather enormous amounts of light.
BIG TELESCOPE WOES
Gigantic telescope mirrors are hard
to build because they bend under their own weight. When a mirror bends, it makes
a blurry image. One way to keep a giant mirror from bending is to divide the
mirror into smaller sections. Another way to avoid huge mirrors is to use
computers to combine images from several telescopes. The Very Large Telescope in
Chile, for example, has four telescopes with 26-foot (8-meter) mirrors. Together
they gather the same amount of light as a telescope with a 52-foot (16-meter)
mirror.
Air causes another problem for
telescopes. The air low in Earth’s atmosphere swirls about. This movement bends
the light coming down from space just a bit, making the images we see through
telescopes appear slightly blurry. To reduce this effect, large telescopes are
often built on high mountains. This puts them above much of the air in the
atmosphere. Many modern telescopes also have flexible mirrors. The shape of
their mirrors can be automatically adjusted hundreds of times a second to adjust
for the swirling atmosphere and keep the image sharp.
TELESCOPES THAT SEE INVISIBLE RADIATION
Optical telescopes are only one
type of telescope. Astronomers also use telescopes that detect other kinds of
electric and magnetic rays from space, such as X rays and radio waves. Our eyes
cannot see these rays. Some objects in space aren’t bright enough to be seen
with visible light. We wouldn’t know they exist without telescopes that can
detect other types of radiation.
A radio telescope, for example,
detects radio waves given off by planets, stars, and other objects in space. It
has a huge dish that collects the radio waves and focuses them on to an antenna
in the center of the dish. The dish can be turned to point at any part of the
sky. The antenna turns the radio waves into electrical signals that astronomers
record and study.
TELESCOPES IN SPACE
Several space telescopes are in
orbit around Earth, beyond the atmosphere. From there, they have a perfectly
clear view into space. This means they can see much more detail on distant
objects.
Some types of radiation, such as
ultraviolet light, X rays, and gamma rays cannot pass through Earth’s
atmosphere. Telescopes that detect these types of radiation must be launched
into space.
THE FIRST TELESCOPES
We do not know exactly who
invented the telescope, but we do know it was invented in Holland at the
beginning of the 17th century. The first person to look into space through a
telescope was the Italian scientist Galileo. He was the first to see moons
orbiting Jupiter, Saturn’s rings, and mountains on the Moon.
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Space
