kovrin sat with tanya all the evening, and after midnight went out with her into the garden. it was...
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Kovrin sat with Tanya all the evening, and after midnight went out with her into the garden. It was cold... "Even as a child I used to sneeze from the smoke here," he said, shrugging his shoulders, "but to this day I don't understand how smoke can keep off frost." - PowerPoint PPT PresentationTRANSCRIPT
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Kovrin sat with Tanya all the evening, and after midnight went out with her into the garden. It was cold...
"Even as a child I used to sneeze from the smoke here," he said,
shrugging his shoulders, "but to this day I don't understand how smoke
can keep off frost.""Smoke takes the place of clouds
when there are none . . ." answered Tanya. "In overcast and cloudy
weather there is no frost.”Anton Chekhov, The Black Monk
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Refraction• Refraction is the
bending of light when it passes from one substance into another
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Example: Refraction at Sunset
• Sun appears distorted at sunset because of how light bends in Earth’s atmosphere
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Angular Resolution• The rings in this
image of a star come from interference of light wave.
• This limit on angular resolution is known as the diffraction limit
Close-up of a star from the HubbleSpace Telescope
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What are the two basic designs of telescopes?
• Refracting telescope: Focuses light with lenses
• Reflecting telescope: Focuses light with mirrors
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Refracting Telescope
• Refracting telescopes need to be very long, with large, heavy lenses
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Reflecting Telescope
• Reflecting telescopes can have much greater diameters
• Most modern telescopes are reflectors
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Designs for Reflecting Telescopes
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Mirrors in Reflecting Telescopes
Twin Keck telescopes on Mauna Kea in Hawaii
Segmented 10-meter mirror of a Keck telescope
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What do astronomers do with telescopes?
• Imaging: Taking pictures of the sky• Spectroscopy: Breaking light into spectra• Timing: Measuring how light output varies
with time
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Light Pollution
• Scattering of human-made light in the atmosphere is a growing problem for astronomy
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Twinkling and Turbulence
Turbulent air flow in Earth’s atmosphere distorts our view, causing stars to appear to twinkle
Star viewed with ground-based telescope
Same star viewed with Hubble Space Telescope
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Adaptive Optics
Rapidly changing the shape of a telescope’s mirror compensates for some of the effects of turbulence
Without adaptive optics With adaptive optics
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Calm, High, Dark, Dry• The best
observing sites are atop remote mountains
Summit of Mauna Kea, Hawaii
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Why do we put telescopes into space?
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How can we observe nonvisible light?
• A standard satellite dish is essentially a telescope for observing radio waves
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Radio Telescopes
• A radio telescope is like a giant mirror that reflects radio waves to a focus
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IR & UV Telescopes
• Infrared and ultraviolet-light telescopes operate like visible-light telescopes but need to be above atmosphere to see all IR and UV wavelengths
SOFIA Spitzer
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X-Ray Telescopes
• X-ray telescopes also need to be above the atmosphere
Chandra
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X-Ray Telescopes
• Focusing of X-rays requires special mirrors• Mirrors are arranged to focus X-ray photons through
grazing bounces off the surface
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Gamma Ray Telescopes• Gamma ray
telescopes also need to be in space
• Focusing gamma rays is extremely difficult
Compton Observatory
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How can multiple telescopes work together?
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Interferometry
• Interferometery is a technique for linking two or more telescopes so that they have the angular resolution of a single large one
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Interferometry
• Easiest to do with radio telescopes
• Now becoming possible with infrared and visible-light telescopes
Very Large Array (VLA)
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Future of Astronomy in Space?