Telescopes

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

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)

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.

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

/ 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

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

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.

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.

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?

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.

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

Spin casting mirrors https://www.youtube.com/watch?v=cBWU7dEImTw

Hale telescope on Palomar Mountain in CA

3 basic reflector types: Cassegrain Newtonian Coude’ focus

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?

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

Schmidt-Cassegrain (catadioptric) telescope combine both refractor and reflector to greatly shorten the body tube and make a large aperture lens very portable. http://science.howstuffworks.com/telescope4.htm to see how a Schmidt-Cassegrain telescope works.

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.

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.

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

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

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.

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

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.

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