Astronomical Observations What Wavelengths To Use? Type Atmosphere Radio Waves No effect Microwaves Mostly blocked Infrared Blocked Visible Light Slight blurring Ultraviolet Blocked X-rays Blocked Gamma Rays Blocked
Lenses and Light Lens Image Incoming Rays Outgoing Rays Focal Plane 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
Lenses and Light Focal Plane Lens Object Eye 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
A Basic Refracting Telescope Focal Plane Image of Point 2 From Point Source 1 Eye Image of Point 1 From Point Source 2 Eyepiece Objective Lens Two lenses together make a telescope Changing the eyepiece changes the magnification The amount of light gathered depends on the size of the objective
What To Do With The Light Prism View directly CCD camera Spectrometer From the Telescope The Spectrometer Uses prism or (more likely) diffraction grating Breaks light into different colors/wavelengths/frequencies
CCD Detector
Mirrors and Light Mirror Incoming Rays Focal Plane Reflected Rays Mirrors can also create images - in some ways, better than lenses Large telescopes are always reflectors
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 Q. 21: Why is the Hubble Telescope in Space?
Space Based Visible Light Telescopes Gaia Several advantages of going to space No atmospheric distortion No light pollution Can see infrared/ultraviolet Hubble Telescope Brite Constellation NEOSSat
Active Optics Incoming Rays Focal Plane Reflected Rays Mirror It is hard to make large mirrors It is easier to make several small mirrors You can use motors & computer to line them up
Adaptive Optics Focal Plane Mirror Light gets distorted by the atmosphere It ends up imperfect at the telescope This ruins the focus, blurring the image
Adaptive Optics Focal Plane Mirror Computers can respond to imperfections Motors can adjust the mirrors This fixes the blurred image
What Wavelengths to Use? Type Atmosphere Radio Waves No effect Microwaves Mostly blocked Infrared Blocked Visible Light Slight blurring Ultraviolet Blocked X-rays Blocked Gamma Rays Blocked Q. 22: The Other Earth-based Observations
Radio Telescopes Antenna Incoming Radio Waves Reflected Radio Waves Reflector 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
Robert C. Byrd Green Bank Telescope, about 100 m Radio Telescopes Robert C. Byrd Green Bank Telescope, about 100 m FAST Telescope, 500 m
Radio Interferometry No atmospheric blurring Background Problem Huge diffraction limit problem (about 1o) Signal can be combined from multiple radio telescopes Effective size is distance between telescopes Effective resolution better than optical
Radio Interferometry Very Large Array
Very Long Baseline Array Radio Interferometry Very Long Baseline Array
What Wavelengths to Use? Type Atmosphere Radio Waves No effect Microwaves Mostly blocked Infrared Blocked Visible Light Slight blurring Ultraviolet Blocked X-rays Blocked Gamma Rays Blocked Mostly restricted to space Limited microwave and IR from Earth
Infrared and Ultraviolet Space Telescopes Spitzer Space Telescope Hisaki Space Telescope
X-Ray Space Telescopes Chandra X-Ray Observatory NuSTAR HXMT Astrosat HETE XMM Newton Swift
Gamma-Ray Space Telescopes AGILE INTEGRAL Fermi Gamma-Ray Space Telescope
End of Material for Test 1 P2 = a3 c = 3 108 m/s c = lf (M + m)P2 = a3 E = h f F = ma Questions? P = knT lmax T = 2900 Km