Astronomical Observations TypeAtmosphere  Radio WavesNo effect  MicrowavesMostly blocked  InfraredBlocked  Visible LightSlight blurring  UltravioletBlocked  X-raysBlocked  Gamma RaysBlocked What wavelengths to use?

Incoming Rays Lens Outgoing Rays Focal Plane Image Lenses and Light  Light waves going through a lens are bent  They converge on the focal plane of the lens  An image forms on the focal plane  The greater the distance to the focal plane, the bigger the image

Eye Object Focal Plane Lens  Working in reverse, a lens can magnify a small object making it look big and far away  The closer the focal plane is, the bigger the image  You can also magnify an image Lenses and Light

Eye From Point Source 2 From Point Source 1 Objective Lens Eyepiece Focal Plane  Two lenses together make a telescope  Changing the eyepiece changes the magnification  The amount of light gathered depends on the size of the objective Image of Point 1 Image of Point 2 Lenses and Light

Prism  View directly  CCD camera  Spectrometer The Spectrometer Uses prism or (more likely) diffraction grating Breaks light into different colors/wavelengths/frequencies From the Telescope What to do with the light

CCD detector

Mirrors and Light  Mirrors can also create images - in some ways, better than lenses  Large telescopes are always reflectors Focal Plane Mirror Incoming Rays Reflected Rays

The largest optical telescopes in the world  Gran Telescopio Canarias  10.6 m diameter  Keck 1 and Keck 2  10 m diameter each

What makes a good telescope  The bigger the diameter, the better  Bigger diameter = more light gathering power  Bigger diameter = less diffraction (blurring)  Avoid atmospheric distortion and light pollution  Space  Mountains  Away from light pollution  Magnification is not the main issue  Eyepiece changes magnification  Outside the solar system, you can never decrease the distance  Too far away

Space Based Telescopes  Several advantages of going to space  No atmospheric distortion  No light pollution  Can see infrared/ultraviolet Hubble TelescopeJames Webb Space Telescope  Launches 2018

Active Optics  It is hard to make large mirrors  It is easier to make several small mirrors  You can use motors & computer to line them up Focal Plane Mirror Incoming Rays Reflected Rays

Adaptive Optics  Light gets distorted by the atmosphere  It ends up imperfect at the telescope  This ruins the focus, blurring the image Focal Plane Mirror

 Computers can respond to imperfections  Motors can adjust the mirrors  This fixes the blurred image Focal Plane Mirror Adaptive Optics

Telescopes are used here on earth to observe visible light from space. Why aren’t they used for infrared and ultraviolet light? A) No astronomical objects produce these kinds of light B) The atmosphere blocks these types of light C) No mirrors or lenses have ever been discovered that can reflect/refract these kinds of light D) Film and CCD cameras can’t detect these types of light What wavelengths to use?

TypeAtmosphere  Radio WavesNo effect  MicrowavesMostly blocked  InfraredBlocked  Visible LightSlight blurring  UltravioletBlocked  X-raysBlocked  Gamma RaysBlocked

Radio Telescopes Reflector Incoming Radio Waves Reflected Radio Waves Antenna  Always use a radio reflector (like a mirror)  High precision reflector is not necessary because radio waves are very long  Most radio sources are quite weak

Arecibo Telescope, 305 m Robert C. Byrd Green Bank Telescope, about 100 m Radio Telescopes

Radio Interferometry  No atmospheric blurring  Background Problem  Huge diffraction limit problem (about 1 o )  Signal can be combined from multiple radio telescopes  Effective size is distance between telescopes  Effective resolution better than optical

Radio Interferometry Very Large Array

Radio Interferometry Very Long Baseline Array

What wavelengths to use?  Mostly restricted to space  Limited microwave and IR from Earth TypeAtmosphere  Radio WavesNo effect  MicrowavesMostly blocked  InfraredBlocked  Visible LightSlight blurring  UltravioletBlocked  X-raysBlocked  Gamma RaysBlocked

Infrared and Microwave Space Telescopes Spitzer Space Telescope Herschel Observatory Wilkinson Microwave Anisotropy Probe Planck Observatory

X-Ray Space Telescopes Chandra X-Ray Observatory XMM Newton Rossi X-Ray Timing Explorer Swift Gamma Ray Burst Telescope

UV and Gamma-Ray Space Telescopes GALEX INTEGRAL Fermi Gamma-Ray Space Telescope