Just as our eyes cannot see small objects, so they cannot
see things that are very far off. Even when things are millions of miles away,
telescopes show them very clearly, The long tubes gather light rays from
distant objects and make magnified images of them that seem nearer. Some
telescopes use lenses to gather light, while others use mirrors.
A pair of binoculars works like two small telescopes joined
together, one for each eye. A gearwheel in the centre of the binoculars alters
the distance between the lenses and brings the image in the binoculars into
sharp focus.
This small, amateur instrument is called a refracting telescope
because the lenses inside it bend or refract light. It is difficult to make
large lenses, so refracting telescopes tend to be small and not very powerful.
The first refracting telescope was built in 1608 by a Dutch scientist, Jan
Lippershey, who lived from about 1570 to 1619.
This is the most powerful type of telescope. It uses mirrors instead
of lenses because large mirrors are easier to manufacture than large lenses and
make better images. A large, central mirror collects light from a distant
object and a smaller mirror reflects the light into the eyepiece.
