Astronomical Observations
What wavelengths to use?
Type
Radio Waves
Microwaves
Infrared
Visible Light
Ultraviolet
X-rays
Gamma Rays
Atmosphere
No effect
Mostly blocked
Blocked
Slight blurring
Blocked
Blocked
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
Lenses and Light
Focal Plane
From Point
Source 1
Image of
Point 2
Eye
Eyepiece
Objective
Lens
Image of Point 1
Two lenses together make a telescope
Changing the eyepiece changes the magnification
The amount of light gathered depends on the size of
the objective
From Point
Source 2
What to do with the light
View directly
CCD camera
Spectrometer
Prism
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
Space Based Telescopes
Several advantages of going to space
No atmospheric distortion
No light pollution
Can see infrared/ultraviolet
Hubble Telescope
James Webb Space Telescope
Launches 2018
Active Optics
Incoming Rays
Focal Plane
Reflected Rays
It is hard to make large mirrors
It is easier to make several small mirrors
You can use motors & computer to line them up
Mirror
Adaptive Optics
Focal Plane
Light gets distorted by the atmosphere
It ends up imperfect at the telescope
This ruins the focus, blurring the image
Mirror
Adaptive Optics
Focal Plane
Computers can respond to imperfections
Motors can adjust the mirrors
This fixes the blurred image
Mirror
What wavelengths to use?
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?
Type
Radio Waves
Microwaves
Infrared
Visible Light
Ultraviolet
X-rays
Gamma Rays
Atmosphere
No effect
Mostly blocked
Blocked
Slight blurring
Blocked
Blocked
Blocked
Radio Telescopes
Incoming Radio
Waves
Antenna
Reflected Radio Waves
Always use a radio reflector (like a mirror)
Reflector
High precision reflector is not necessary because
radio waves are very long
Most radio sources are quite weak
Radio Telescopes
Robert C. Byrd Green Bank
Telescope, about 100 m
Arecibo Telescope, 305 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
Radio Interferometry
Very Long
Baseline Array
What wavelengths to use?
Type
Radio Waves
Microwaves
Infrared
Visible Light
Ultraviolet
X-rays
Gamma Rays
Atmosphere
No effect
Mostly blocked
Blocked
Slight blurring
Blocked
Blocked
Blocked
Mostly restricted to space
Limited microwave and IR from Earth
Infrared and Microwave Space Telescopes
Spitzer Space
Telescope
Wilkinson Microwave
Anisotropy Probe
Herschel
Observatory
Planck Observatory
X-Ray Space Telescopes
Chandra X-Ray Observatory
Rossi X-Ray Timing
Explorer
XMM Newton
Swift Gamma Ray
Burst Telescope
UV and Gamma-Ray Space Telescopes
GALEX
INTEGRAL
Fermi Gamma-Ray
Space Telescope