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ASTRONOMY NOTES: GROUND-BASED TELESCOPES Atmospheric Windows Areas in the EM spectrum where the atmosphere is transparent and the radiation can pass through to the Earth’s surface. Earth has 2 atmospheric windows • Radio • Visible Therefore, there are 2 main types of groundbased telescopes. Optical Telescopes Focus light into an image. Light is collected by lens or mirror OPTICAL TELESCOPES Basic Optics: Reflecting Telescope Basic Optics: Refracting Telescope How it works Problems Refracting Telescope Reflecting Telescope Bends light through a lens to form an Curved mirror reflects light to form an image image Eyepiece magnifies the light Eyepiece magnifies the light • UV light is absorbed by lens and dims the image • Lens must be large to improve magnification Chromatic Aberration o Very expensive o Lens can only be supported from sides and may sag under its own weight • Difficult and expensive to make lens without defects • Chromatic aberration Reflecting telescope is an improvement of the refracting telescope • Light is reflected before passing through lens ! no chromatic aberrations • Do not need high quality optical glass o Cheaper o Can be made larger ! bigger mirror, collects more light = better image • Mirror can be supported from the back ! will not sag • Tend to be shorter Check Point 1. What does refract mean? a. Light rays are absorbed as they pass into a different medium b. Light rays bounce back as they pass into a different medium c. Light rays change direction as they pass into a different medium 2. Which way do light rays bend through a convex lens? a. Together at a converging point b. Away from each other – they diverge c. They do not pass through, they bounce back 3. What types of lenses are used in refracting telescopes? a. Converging b. Diverging c. No lenses are used Radio Telescopes Used to study naturally occurring radio waves from stars, galaxies, quasars and other celestial objects. Has two main parts • Primary reflector surface • Antenna Radio Telescopes: Advantages • Can be used in poor weather conditions (cloudy, etc) • Can be used during the day Radio Telescopes: Disadvantages • Radio waves may be large, so radio telescopes must be large • Very expensive