Lecture 7

Announcements ● HW 3 due 2/8 at midnight ● Telescope observing lab - sign up for spots Observing with Telescopes (RRRT Lab) What are the two most important properties of a telescope? ● Light-collecting area (or light gathering power) : telescopes with a larger collecting area can gather a greater amount of light in a shorter time ● Angular resolution : Telescopes that are larger are capable of taking images with greater detail. Angular Resolution ● The minimum angular separation that the telescope can distinguish Misconception: The size of the Rising Moon ● Many people believe the rising moon is larger than when the Moon is high overhead ○ The Moon is actually slightly larger when it is high overhead! ● The angular size of the Moon is always about 0.5 degrees (as is the Sun) Angular Measurements ● Full circle = 360 o ● 1 o = 60’ ( arcminutes ) ● 1’ = 60” ( arcseconds ) ● Notes: 1 arcsecond is the size of a U.S. quarter as seen from 5km (3 miles) or a penny as seen from 2.2 miles Angular Size: Radians ● A more practical way to measure angles is through the use of the ‘radian’ ● 360 degrees = 2π radians Angular Resolution ● Ultimate limit to resolution comes from interference of light waves within a telescope ● Larger telescopes are capable of greater resolution because there is less interference The Diffraction Limit ● See mathematical insight 6.2 in book ● The smallest detail that a telescope can resolve is given by ● = 2.5E ? 5 * (wavelength of light/diameter of telescope) [arcseconds] ● = 2.5E ? 5 λ/D ● They must be in the same units Best Scientific Observing Sites