Spectrographs, Radio Telescopes & Space Telescopes

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Spectrographs, Radio Telescopes & Space Telescopes
Astr100 Lecture 10 September 19, 2012

Keck 10-meter Telescopes Mauna Kea Observatory, HI

Keck Telescope Details

University of Arizona Mirror Furnace

TMT = Thirty Meter Telescope Now in design phase. Cost $800M

Thirty Meter Telescope details: 492 segments each 1-m across

Active & Adaptive Optics
• Active optics – to adjust a big mirror once every minute or so to maintain its mechanical shape • Adaptive optics – to adjust a small mirror (in the telescope beam) up to 2,000 times per second to cancel the blurring effects of the Earth’s atmosphere • Both techniques involve computer control of motors that move a fraction of a wavelength

Atmospheric “seeing”

Atmospheric blurring: due to air movements

Instruments for Telescopes
• Cameras are sensitive to specific wavelengths:
– UV, visible, or infrared wavebands

• Different spectrographs for different purposes:
– to measure Doppler shifts of galaxies – to study conditions in stars and nebulae – to watch stars’ velocities wobble very small amounts to detect planets around other stars

CCD = Charge Coupled Device
• Wafer of silicon with ion implants to define pixels • Pixels = picture elements • Photons hit the surface and create an image by separating electrons from the parent atom • The electrons are moved across the silicon surface, sent to a “horizontal register”, and sent out to a computer memory. • CCDs were developed in the 1980’s by engineers and astronomers.

CCD Camera Array

Prism Spectrograph

Grating Spectrograph

I-Clicker Quiz: Who designed and built the first reflecting telescope? a. Galileo b. Tycho Brahe c. Isaac Newton d. Kepler

History of Radio Astronomy
• Karl Jansky: first to detect radio waves from space: 1932 • Grote Reber in Wheaton, IL was first to survey the sky for radio sources 1936-1944. He built the first radio telescopes. • Ryle & Hewish won 1974 Physics Nobel Prize for...
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