Page 254 - Inventions - A Visual Encyclopedia (DK - Smithsonian)

Studying the stars

People have been fascinated by stars and planets since prehistoric times, but
for thousands of years they could only study them with their unaided eyes.

In the 17th century, telescopes opened up new ways of seeing the universe,
and astronomers have been building bigger and better instruments ever since.

SPACE Reflector Photo of Orion nebula, 1883 Infrared camera view, 2010
telescope, 1724

WHAT IS A TELESCOPE?
Telescopes use a large lens or mirror to
collect light, and a smaller lens called the
eyepiece to create images of distant objects ASTROPHOTOGRAPHY
that are brighter and larger than those After the invention of photography in the 19th century,
formed by our normal eyesight. The astronomers soon attached cameras to telescopes. Cameras
principle was discovered by the Dutch can collect light over long periods, creating bright images
lensmaker Hans Lippershey around 1608. that reveal much more detail than human eyesight can
detect. Modern electronic cameras can detect types of
light, such as infrared, that are invisible to human eyes.

TYPES OF TELESCOPE

Refractor telescopes were the first telescopes to be invented. They use large lenses to
bend light rays so they cross at a focal point. Reflector telescopes use curved mirrors ▶ THE VERY LARGE
to bounce light rays to a focus. As the light rays spread apart again, one or more lenses TELESCOPE (VLT)
in the eyepiece alter their paths to create a magnified, or enlarged, image. This is one of four
huge telescopes built
4. Light passes 3. Secondary by the European
1. Light rays through the mirror reflects light Southern Observatory
2. Objective lens from source to the eyepiece
gathers light eyepiece lens, in Chile’s high desert.
and focuses it at which magnifies Each telescope contains
the focal point the image a mirror that is 26 ft
(8 m) wide and weighs
24 tons. Using the VLT
Focal point reveals images that are
1. Light rays four billion times fainter
from source
than the unaided eye
3. Light passes through 2. Primary mirror reflects can detect.
the eyepiece lens, which incoming light rays to the
magnifies the image secondary mirror
Refractor telescope Reflector telescope

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