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A telescope has often been called a
"light bucket," as its purpose is to collect as much light as
possible. This is done by increasing the aperture, but as the
aperture increases in size, so must the length of the tube. In the
late 1600's, two of the early astronomers, Huygens and
Hevelius, in their quest to see more of our Universe, built telescopes
up to 200 feet long. A major problem with such large telescopes
was the fact that the edges of a lens are much thinner than the
center. As it become larger, it becomes heavier and increasingly
difficult to mount. The world's largest refractor telescope was
built in 1897 at Yerkes Observatory in Wisconsin. It has a lens
diameter of forty inches and is still in use today. It is at the
upper limit of size at which a refract telescope can be structurally
stable. If its lens were any heavier, it could not be supported
around its edges by current technology.
A reflector telescope does not suffer from this
limitation because its uses a mirror to collect light, rather than a
lens; thus they can be quite large. The telescopes used by all the
great observatories use this design. The world's largest is the
Keck Telescope at Mauna Kea Observatory in Hawaii. It was build
with a 394 inch diameter mirror and has been operational since 1991.
A refractor telescope certainly fills the needs
of budding astronomers, but as skill and knowledge increase, they want
to probe deeper and deeper into the secrets of the Universe, and this
can only be done with a telescope having a large aperture. Per
inch of aperture, reflector telescopes cost significantly less than
refractor telescopes. |
|
Galileo Refractor |
Newton Reflector |
| Aperture |
Lens collects light |
Mirror collects light |
| Viewing moon, planets and Sun |
Excellent |
Good |
| Viewing deep space - galaxies, nebula, etc. |
Good |
Excellent |
| Terrestrial Viewing |
Good |
Not suitable |
| Ease of Use |
Very Easy |
Less Easy |
| Reliability |
Very sturdy |
More fragile |
| Maintenance |
Minimal to None |
Required |
| Large Aperture Scopes |
Bulky and Heavy |
Compact and light |
| Cost per inch of aperture |
higher |
lower |
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