Telescope Lesson Plan
Developed by Harry Singh
May 16, 2002

There are two main types of telescopes, Refractors and Reflectors. Refractors are the most popular telescope for beginners. They use a lens to gather and focus the light of the object it's pointing at. Using a lens which is made from two elements or more, the refractor reduces false colors. There are two different types of refractor telescopes, achromatic or apochromatic.

Characteristics of Refractor telescopes

• small and compact
• maintenance free
• high resolution (excellent planet scopes)
• can be used during the day for terrestrial viewing without the image being upside down
• expensive for larger models and apochromatic
• less light gathering power than reflecting telescopes because of their smaller size
• awkward to use when pointing straight up (straight up is the best place to view with a telescope)
• false color especially in larger models

Reflectors gather light using a mirror which is curved. The curved mirror concentrates the light and is then magnified by an eyepiece. Newtonian reflectors (invented by Sir Issac Newton) can be identified by the eyepiece protruding from the side of the telescope. These are the most common and cheapest to buy. Other types of reflectors incorporate a front lens which corrects the incoming light first before hitting the main reflective mirror. These front lenses are called corrector plates and the different types used determine the type of reflecting telescope. The more popular types are the Schmidt-Cassegrain and the Maksutov-Cassegrain.

Characteristics of Reflecting telescopes

• excellent light gathering power - the bigger the better
• cheapest per centimeter of aperture
• wider field of view than refractors
• some maintenance required (re-coat the mirror faces every 8-10 years, re-align mirrors if necessary)
• optics are not enclosed, but can be cleaned occasionally
• lower resolution due to secondary mirror obstruction, generally suited better for faint objects

See http://www.telescopes-astronomy.com.au/telescopes003.htm for more information.

Assignments

• Use SeekAWord applet with relevant vocabulary list (Telescope, Reflector, etc.)