1. Telescopes

2. Most missed question On last test
Molecules produce emission spectra that are more complex – since there are more bonds and atoms involved.
Most missed question
On last test

3. Optical Telescope Function – Aids in 2 ways:
Collects more light than the naked eye.
2. Magnifies images - Allows more detail!
What appears to be one star may actually be two (eclipsing binaries)

4. Location, Location, Location!
Best location for telescopes is:
Mountain top – Less air = less light
diffraction off molecules.
Dry Climate – less H2O in air.
Remote areas – Less light pollution.

5. Optical Telescopes use lens(es) and mirrors to gather and focus light.
Light gathering power is proportional to area of lens. Since they are circular, the area is:
pr2

6. / Pr2 Pr2 = = 625 156.25 = 4 Four times more light gathering!
Doubling the radius increases light gathering power how many times? /
Pr2
Pr2 =
= 625
156.25
= (25) 2
(12.5) 2
= 4 Four times
more light
gathering! r2

7. Get in groups of two to present the following topics next week
Get in groups of two to present the following topics next week. You will be given Thursday and Friday class time to work on this, with the only grade being “on-task.”
Radio telescopes
I.R. and U.V. telescopes
U.V., Gamma, & X-ray (high energy)
telescopes
Interferometery
Telescope size
High Resolution Astronomy
Other Astronomies

8. Telescopes are stored in a dome roof building
in order to view the entire sky.
TEMPERATURE is kept stable (cool in building to match outside air) for two reasons:
Glass expands & contracts with temperature
changes causing distortion of image.
Air turbulence (in telescope body) blurs the
image as well. Like heat waves off hot
pavement of a highway in the Summer.
Dome must move smoothly and same speed
as Earth’s rotation to stay fixed on object and
not blur the image.

9. Refracting Telescope – Uses 2 lenses
Objective lens – Gathers light and refracts (bends) light to concentrate image.
Eyepiece lens – Magnifies the image for us to see.

10. Built in 1895 – Why were most refractors built prior to 1900?
Largest objective lens Refractor telescope is 102 cm diameter – Yerkes observatory in Wisconsin.
Built in 1895 – Why were most refractors built prior to 1900?

11. Why not build refractors anymore?
Glass lens MUST be ground perfect on both
sides to avoid any blurring.
Pure glass must be used to avoid any
diffraction within the lens.
Glass moves over time, therefore must be rotated routinely.
EASIER and cheaper to make mirrors in a
parabolic shape than to grind two sides of a
lens.

12. Reflecting Telescopes
Use mirrors for objective.
Glass is coated with a shiny metal
(aluminum) on back to make a mirror.
OBJECTIVE mirrors can be made LARGE.
Hale telescope on Palomar Mountain in CA
is 5.08 meters in diameter!
Reflector versus Refractor

13. Spin casting mirrors

15. Hale telescope on Palomar Mountain in CA

16. 3 basic reflector types:
Cassegrain Newtonian Coude’
focus

17. Why/when is this type useful?
Prime focus Reflector – the image is focused at the opening of the body.
Why/when is this type useful?

18. When viewing in a large dome with a large telescope, the viewer can sit at the “prime focus” and view straight away.

19. Schmidt-Cassegrain (catadioptric) telescope combine both refractor and reflector to greatly shorten the body tube and make a large aperture lens very portable.
to see how a Schmidt-Cassegrain telescope works.

20. Assignment - In pairs:
A.) Research the importance of “Focal length ratio” and how it makes some telescopes better for viewing planets and nebulae.
B.) Explain the following paragraph regarding Schmidt-Cassegrain telescopes:
Schmidt-Cassegrain catadioptrics do not have as wide a contrast range on the Moon and planets as a refractor or most f/6 to f/8 reflectors, because of the extra light scattered by its larger secondary mirror and its multiple-element folded light path, nor will it be able to split close binary stars as cleanly. However, a Schmidt-Cassegrain will usually outperform a fast (f/4.5)focal ratio reflector of similar aperture on the planets and binary stars due to its lack of diffraction-causing secondary mirror spider vanes. A Maksutov-Cassegrain, because it has a smaller secondary mirror obstruction, typically has better contrast than a Schmidt-Cassegrain, often rivaling that of a refractor of similar aperture.

21. MMT – Multi-mirror Telescopes
Many mirrors instead of one – easier and cheaper to make small mirrors well!
First MMT in 1979 in Arizona
Keck I and Keck II in Hawaii give
best resolution of any land scope.

22. Keck I and II high above the clouds –
notice the snow on the ground.
Little atmospheric blurring
Little light pollution
little moisture to hinder incoming light

23. Other Optical Telescopes
A. Schmidt Telescope – Use both a
reflecting and a refracting lens.

24. B. HST (Hubble Space Telescope )
Orbits above Earth (610 Km high)
No Atmosphere intereference.
Detects U.V. rays which do not traverse Earth’s atmosphere. It detects a broader spectrum!
Solar Powered – constantly ON.

25. Devices to improve images
Photographic plates – can collect
“light information” (Photons) for
hours, which intensifies the image
and makes a permanent record.

26. 2. CCD – Charged coupled device is photocells which collect electrons as light (photons) hit the receptor and magnifies the image.
Quicker and Better – Very sensitive.

27. Study, read, listen to your peer
presentation of, and know:
Radio telescopes
I.R. and U.V. telescopes
U.V., Gamma, & X-ray (high energy)
telescopes
Interferometery
Telescope size
High Resolution Astronomy
Other Astronomies