5.3 Collecting Light with Telescopes

Our goals for learningHow do telescopes help us learn about the universe?Why do we put telescopes into space?How is technology revolutionizing astronomy?

How do telescopes help us learn about the universe?Telescopes collect more light than our eyes light-collecting areaTelescopes can see more detail than our eyes angular resolutionTelescopes/instruments can detect light that is invisible to our eyes (e.g., radio, infrared, ultraviolet)

Bigger is betterLarger light-collecting area

Better angular resolution

Bigger is better

Angular ResolutionThe minimum angular separation that the telescope can distinguish.

Angular resolution: smaller is better?

Basic Telescope DesignRefracting: lensesRefracting telescopeYerkes 1-m refractor

Basic Telescope DesignReflecting: mirrorsMost research telescopes today are reflectingReflecting telescopeGemini North 8-m

Keck I and Keck II Mauna Kea, HI

Mauna Kea, Hawaii

Different designs for different wavelengths of lightRadio telescope (Arecibo, Puerto Rico)

*Tool from the Telescopes tutorial. *Emphasize that at a great distance the lights would look like one light rather than two --- but we could still see them. (Students sometimes think that below a particular angular resolution we see nothing at all.) *Can use this table to discuss largest current telescopes and note how many new large telescopes have been recently built. E.g, Palomar, which was largest for some 40 years, no longer even in top 10 Plans in work for next generation of much bigger telescopes: 30 meter, 50 meter *Show students the correspondence between the diagram and the photograph (I.e., point out the primary and secondary mirrors). *A few cool telescope slides