Chapter 6: Telescopes

         By using telescopes, we can see the incredible sights of the cosmos
         Galileo first used a telescope for astronomy, saw Jupiter in detail
         With modern telescopes, We can see this!

The abilities to focus and detect light are fundamental to eyes, cameras, and telescopes
         Eyes (the most common example):
                  Retina: detects the light
                  Lens: focusses the light so that an image of the original object
                           appears on the retina
Diagram
         Cameras:
                  Detector: film or CCD
                  Focussing: lens
Diagram
         Telescopes:
                  Detector: can be human eye, film, CCD
                  Focussing: can use lenses ("refracting telescopes") or
                           mirrors ("reflecting telescope")
                  Refracting telescope diagram and example (Yerkes obs. in Wi.)
                  Reflecting telescope diagram of simple design and
diagram of more complex design

Important Abilities of Telescopes:
         Collect many photons
                  light collecting area = pi (diameter/2)²
         Resolve objects that are separated by small angles
angular separation
                  calculating angular size: figure
                  "Angular resolution" = smallest angular separation
                           where you can still see that 2 objects
                           are actually 2 objects rather than 1 blobby object
                  The human eye's angular resolution = 1 arcminute
                  The Hubble Space Telescope's ang. resolution = 0.05 arcseconds
Hubble Deep Field
                  Diffraction limit
                           Light waves spread out when they go through holes (lenses)
                           "diffraction limit" = 2.5 x 10⁵ arcsec * wavelen./diameter

Question: Suppose that two stars are separated on the sky by
         0.1 arcseconds. What will you see if you look at them with a
         telescope that has an angular resolution of 0.01 arcseconds?
         What will you see if you look at them with a telescope that has
         an angular resolution of 0.5 arcseconds?

How do we learn from telescopic observations of the heavens?        
         Imaging: Crab Nebula example
                  This is a combination of images in various colors and false colors
         Spectroscopy: spectrum from Mars
                  Resolution: high spectral resolution example and
low spectral resolution example
         Timing: Example of light curve from binary star

Atmospheric effects
         Clouds, light pollution, distortion, absorption
         Solutions: put telescopes on mountains, on satellites in space,
         or quickly adjust optics ("adaptive optics")

Why we want to see other wavelengths of light:
         Orion in the Visible, IR, and UV
         Crab nebula in radio, IR, Optical, and X-ray
         The Milky Way in Gamma-ray, X-ray, Visible, IR, and Radio
Tricks for detecting other wavelengths:
         Infrared (SIRTF) --> cool the detector (ex of blackbody: bright human)
         X-rays (Chandra) --> nested mirrors
         Radio waves have very large wavelengths, so need
                  Huge telescopes (Arecibo, diameter = 305 meters
                  and Green Bank) or
                  "Link" several telescopes together to get better angular
                  resolution. (Very Large Array (VLA))
                  = 27 telescopes 25m over 36km

Supplemental Material:

Microwave Anisotropy Probe the Cosmic Microwave Background
Hubble Space Telescope: the Hubble Deep Field
Gamma rays: Compton (GRO)
If you can afford it get a close-up.
         Earth-orbiters
         Flybys
Voyager2 to the Giant Planets – the Grand Tour
         Orbiters
Cassini to Saturn
         Landers/probes
                  Mars Rovers