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Transcript
Telescopes
L1
Purpose of this Lab
• Telescopes:
See
Use
Understand
L1
What is the Purpose of a Telescope?
1. Increase the amount of light we see.
Sensitivity is proportional to Collecting Area.
S = a constant times p(D/2)2
If D increases, then S increases by D2
•
If your telescope is 3 times bigger than mine, then your
telescope can see 32 = 9 times fainter objects than mine.
•
Can you read a book at night? What’s the faintest
star you can see with your naked eye?
L1
Sensitivity
L1
What is the Purpose of a Telescope?
2. Increase the detail (resolution) we see.
Resolution is inversely proportional to Telescope Diameter.
 = a constant times l/D
 Diffraction Limit
If D increases then  decreases by the same amount.
•
If your telescope is 3 times bigger than mine then you can see 3
times smaller angles (3 times smaller objects or detail).
•
Can you read a street sign a block away? Can you see the
binary star in the Big Dipper with your naked eye?
L1
Resolution
L1
Types of Telescopes
L1
Refractor
L1
optical
Yerkes 40-inch refractor
L1
Reflector
L1
Hooker 100-inch reflector
optical
L1
Keck twin 10meter reflector
optical/IR
L1
Arecibo 300-foot reflector
radio
L1
Atmospheric Seeing
L1
• Seeing degrades resolution
• Adaptive optics can recover
resolution
• Engineering limits telescope
size
L1
Resolution and Seeing
Neptune with the Palomar 200-inch reflector
L1
Seeing and Magnification
• Larger than a few inches, a telescope’s resolution
stops getting better due to seeing.
• Don’t be fooled by advertisements claiming huge
magnification increases!
– “Amazing 500X magnification!”
• But sensitivity ALWAYS increases with bigger
telescopes.
L1
Magnitude
Scale
• The SMALLER the
number the BRIGHTER
the star!
• Every difference of 5
magnitudes is a 100X
difference in
BRIGHTNESS.
• Every difference of 1
magnitude = 2.5X
brightness
L1
Magnitude vs. Brightness
Mag.
Difference
1
Factors of 2.5
2.51 = 2.5
Brightness
Diff.
2.5
2
2.52 = 2.5 X 2.5
6.3
3
2.53 = 2.5 X 2.5 X 2.5
16
4
2.54 = 2.5 X 2.5 X 2.5 X 2.5
40
5
2.55 = 2.5 X 2.5 X 2.5 X 2.5 X 2.5
100
6
2.56 = 2.5 X 2.5 X 2.5 X 2.5 X 2.5 X 2.5
250
L1