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Optics and TelescopesKathy Cooksey
Acknowledgements Tyler Nordgren & Julie Rathbun University of RedlandsJohnny B. Holmes Christian Brothers University
Outline• Optics and telescopes• Understand different
types• Why does size matter?• Why put them in
space?
Model Optical Rail
• http://www.school-for-champions.com/science/experiments/simopticsmirror.htm
• Magnification• Image Inversion• Multiple optics
– Image re-inversion ;)
Purpose of Telescope
1. Increases amount of light we see:Sensitivity is proportional to collecting area.If one telescope is 3 times bigger than another, then it can see 32 = 9 times fainter objects.
2. Increases detail (resolution) we see:Resolution is inversely proportional to telescope diameter.If one telescope is 3 times bigger than another, then it can see 3 times smaller angles (3 times smaller objects or detail).
Resolution
Andromeda Galaxy Copyright by AURA
(a) 10’(b) 1’ (10 times bigger than a)(c) 5” (12 times bigger than b)(d) 1” (5 times bigger than c)Human eye: 0.5’ in visual range
Side Note: Exposure Time
• Point telescope, open shutter, and expose for a long time (integration)
• Gather more photons and improve image
• Human eye has limited integration time
Telescopes & Light
• Collect “light”– Visible light is just part of whole spectrum of “light”
• Light is all astronomers have!!!• Electromagnetic spectrum (EM): whole range of
varieties of “light”:– Example: visible light comes from lamp in your house
– Example: radio waves come from radio station
– Other types of radiation: microwaves, infrared and ultraviolet light, X-rays, and gamma-rays
Reflecting Telescope
Light from far away mirror
focuses
light
Problem: how do we get to focused light without blocking incoming light?
Reflecting Telescope
Light from far away mirror
focuses
eyepiece light
Solution #1: If mirror is big enough (say100 to 200 inches in diameter), we can sit right in middle and won’t block much light - this is called prime focus.
Reflecting Telescope
Light from far away eyepiece mirror
focuses
light
Solution #2: Use secondary mirror to reflect light off to side of telescope - this is called Newtonian focus.
Reflecting Telescope
Light from far away primary mirror
focuses
light
eyepiece
Solution #3: Use secondary mirror to reflect light out back of telescope - this is called Cassegrain focus.
Some Large Optical TelescopesAperture(meters)
Name Location Comments
Keck mirror composed of 36 segments10.0
Keck II
Mauna Kea,Hawaii
future optical interferometry!
9.2 Hobby-EberlyMt. Fowlkes,Texas
very inexpensive: sphericalsegmented mirror; fixedelevation; spectroscopy only
8.3 SubaruMauna Kea,Hawaii
NAOJ
Antu
Kueyen
Melipal8.2
Yepun
Cerro Paranal,Chile
now operate independently in thefuture will be units of Very LargeTelescope
Gemini NorthMauna Kea,Hawaii
8.0
Gemini SouthCerro Pachon,Chile
twins
3.0 ShaneMountHamilton,California
Lick Observatory
Loca
tion
, lo
cati
on
, lo
cati
on
Keck Primary Mirrors
• Large!
– Formed by 36 individual
hexagonal segments
• All must be kept positioned relative to their neighbors– To accuracy of four
nanometers, or 1,000 times
thinner than human hair