The Spitzer space telescope orbits 353 miles above the gasses that blanket our planet. But if youwant to look at the stars, you’ll have to settle for looking through Earth’s atmosphere. The amazing thing is that you can! Here’s how:
A telescope is a tool for collecting lots of light. The light makes up an image. Lenses or mirrors inside a telescope squeeze lots of light down to a size the human eye can handle. Speaking of the eye . . . that’s a good place to start!
The size of your pupil is its aperture. In the dark, your pupil gets larger to let in more light. The opening of a telescope is like your pupil in the dark. It is large to let in a lot of light. Even an inexpensive telescope gathers about 200 times more light than your pupil.
Your eye has a lens to focus light onto the retina—the “screen” on the back of your eye. Telescopes use lenses and mirrors to focus lots of light down to fit your retina. The shape of lenses or mirrors manage that trick.
CONCAVE LENS
Surfaces curve in. Light waves are slowed down as they bend outward.
CONVEX LENS
Surfaces bulge out. The thicker the glass, the more light waves are slowed down. So light bends inward, coming to a point beyond the lens.
Every lens has a focal length. It is the distance it takes for a lens to bring light to a point. If you have used a magnifying glass to burn a leaf you have figured out focal length.
There are two main types of telescopes.
Refracting telescope—The telescope Galileo developed 400 years ago was this type.
Good for viewing at distances on Earth or for large objects above, like planets, moons, and stars. Limited in size because large diameter lenses are expensive, heavy, and hard to grind accurately.
Objective lens—Large lens collects as much light as possible.
Tube—Adjusts lenses to the right distance from each other. Keeps out dirt and light.
Eye lens—Takes tiny image from the focal point of the objective lens and spreads it back out just enough to fill your eye’s screen.
Reflecting telescope—Albert Einstein used this type. It is good for viewing faint galaxies, nebulas, and star clusters.
Tube—Not adjustable. Open, so must be kept clean.
Aperture—Opening can be large to allow in the most light possible.
Eye lens—Side mount can be more comfortable for the viewer.
Mirror—Shape is concave (bowl-shaped). Must be kept adjusted.
Lift up your eyes on high and see: Who created these? He who brings out their host by number, calling them all by name; by the greatness of His might and because He is strong in power, not one is missing. — Isaiah 40:26
