Telescopes I. Refraction: Refraction is the _____________ of light as it passes through glass. II. Reflection: Reflection occurs when light _____________ off of a mirror. F f

Light focuses at different points. Light focuses at one point!!

Chromatic Aberration with Glass Lenses Remember Newton’s prism! Bad news!!

III. Telescopes: A. A ____________ telescope uses glass lenses to collect and focus the light. B. The primary component of a ____________ telescope that collects and focuses the light is a mirror.

IV. Two Main Types of Reflecting Telescopes: A. Newtonian 1. The original reflecting telescope. Made by Isaac Newton 2. Simple. Commonly used in smaller amateur telescopes. B. Cassegrain 1. More compact. 2. Commonly used for the larger telescopes

V. Why Do Astronomers Want to Build Larger and Larger Telescopes? A. The larger the primary mirror of a telescope, the more _______ it can collect. This means it can see ____________ objects and take images in a ___________ period of time. B. The larger the primary mirror, the better the ___________. Larger telescopes can see more detail. θ = angular separation (in radians)  = wavelength of light being collected D = diameter of the primary mirror or lens

VI. Preferred Location of Telescopes A. The turbulence of the atmosphere causes the light passing through it to be ____________. We see this as twinkling of the stars. Astronomers see this as a problem that prevents them from obtaining nice clear images. B. As a result, most major observatories are place on the top of _____________ to get above as much of the Earth’s atmosphere as possible. C. Even on the tops of mountains, there is distortion from the Earth’s atmosphere, plus the Earth’s atmosphere absorbs many wavelengths of light. The ultimate, distortion-free environment is to observe from ______________. The primary drawback of observing from space is the expense.

VII. Adaptive Optics A. This is a method to compensate for the atmosphere’s turbulence that is _______________ than sending the telescope into space. B. A fairly bright star is monitored. As this bright star moves around due to the turbulence, a deformable secondary mirror makes ___________ of adjustments ____________to correct the image.

VII. Adaptive Optics A. This is a method to compensate for the atmosphere’s turbulence that is _______________ than sending the telescope into space. B. A fairly bright star is monitored. As this bright star moves around due to the turbulence, a deformable secondary mirror makes __________ _________ adjustments to correct the image.