4 Pages
Unlock Document

Physics, Engineering Physics and Astronomy
ASTR 101

Telescopes • Early telescopes first importantly used by Galileo were refractor telescopes which use a glass lens to focus light of distant objects to a point  A big objective lens sits at the front of the telescope where its diameter determines how much light is collected  An eyepiece magnifies the focused image however nowadays most telescopes are fitted with special instruments or cameras to analyze the data Telescopes Gather Light: • Magnification makes little difference when observing stars as they are too far away  Telescopes are useful because they capture the light and focus light from faint/dim objects  Most important dimension of the telescope is the diameter  Larger diameter = more light (which is why pupils dilate in the dark) • Light-gathering power of a telescope is directly related to the size of the objective lens (location of light gathering)  The area of the objective lens is related to the square of the diameter Optical Telescopes: • Magnification: Not important today however was important with optical telescopes in terms of the eyepiece, as the eyepiece is what magnified the refracted image  Too much magnification would produce blurriness and dimness as the amount of light coming from the object does not change and the atmosphere blurs out surficial details • Resolution: Unlike radio telescopes, building a larger telescope does not compensate for poor resolution as it is the atmosphere that causes blurring • Light Intake: This is why telescopes are built so large; to collect more light  Analogy: If you want to wash your laundry in rain water, you would collect it with large tubs rather than cups Uses of Telescopes: • Surveys: Astronomers generally use telescopes with a fixed program in mind, such as observing how stars are moving around in a nearby galaxy  Astronomers do not sit there looking for stars, they come across them during surveys • Observing technique: Eyepiece is rarely used and most distant objects are observed by computers who accumulate the light over time and produce images  The eye is very unreliable and does not accumulate the light, so faint objects continue to look faint Problems with Refractors: • Chromatic aberration: When light passes through the objective lens, the wavelengths of light are split at different angles and therefore do not have a common focus  Bringing one wavelength of light (ex. Yellow) into focus will cause another to go out of focus (blue)  Can be corrected using cemented doublets; two lenses composed of different materials stuck together with clear cement  Lenses are expensive so more than two is impractical  Does not completely remove chromatic aberration  Longer focal lengths reduce it which is why old refractors were so large • Length: Best images come from thin
More Less

Related notes for ASTR 101

Log In


Join OneClass

Access over 10 million pages of study
documents for 1.3 million courses.

Sign up

Join to view


By registering, I agree to the Terms and Privacy Policies
Already have an account?
Just a few more details

So we can recommend you notes for your school.

Reset Password

Please enter below the email address you registered with and we will send you a link to reset your password.

Add your courses

Get notes from the top students in your class.