Description: In a reflecting telescope or mirror telescope, the main optical element is a mirror, the "primary mirror", which gathers infalling light. Mirror telescopes are often characterized by primary mirror diameter, ranging from 10 centimeters for smaller amateur telescopes to eight meters for the largest solid mirrors used in professional telescopes. Still larger collecting areas can be obtained by combining several mirror segments, which then act in a way similar to that of a larger solid mirror. There are several types of mirror telescopes. For example, in a Newtonian telescope, the light coming from the primary mirror is reflected sideways by a smaller, flat mirror into an eyepiece or a camera. In a Cassegrain telescope, a smaller, convex secondary mirror reflects the light back through an opening in the main mirror.

Related Terms:

• Refracting Telescope
• Telescope
• Mirror

Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

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