A.  Electromagnetic waves -- carry energy through space and matter

      1.  Electromagnetic radiation includes radio waves, microwaves,  infrared waves, visible light, ultraviolet light,  x-rays and gamma rays.

      2.  Electromagnetic spectrum --  electromagnetic radiation arranged by wavelength and frequency.

           a.  Forms of electromagnetic radiation differ in their frequencies, or in the number of waves per unit of time.

           b.  The shorter the wavelength, the more waves that will occur in a given period of time.

           c.  A wavelength is the distance from one wave crest (apex) to the next crest (apex).

      3.  All electromagnetic waves travel at the speed of light, or 300,000 km/sec.

B.  Optical Telescopes -- use light to produce magnified images.  Limited by weather and light pollution.

     1.  Refracting telescopes -- have 1 convex lens.

     2.  Reflecting telescopes -- have 2 lenses, (1 convex, 1 concave).

     3.  Optical telescopes are often located in buildings call observatories, which often have roofs that can be opened for night viewing.

     4.  The Hubble Telescope is located outside the Earth's atmosphere and is in an orbit around the Earth.

     5.  Most observatories are located high on mountain tops above the Earth's low altitude weather and light pollution, where the atmosphere is thinner and dryer.

     6.  Active optics --  computer systems that help correct poor quality images produced by large optical telescopes.

     7.  Adaptive optics -- lasers that relay information to computers of large optical telescopes to adjust the telescope's lenses and mirrors to compensate for atmospheric problems.  Helps adjust the telescope lenses.

C.  Radio Telescopes -- studies radio waves (very long wavelengths) that travel through space.  Does not produce an image.

      1.  Because radio waves pass freely through the atmosphere, radio telescopes are useful 24 hours a day.

      2.  Scientists use information from radio waves to detect objects in space, map the universe, and look for signs of life on other planets.