Astronomy 1010

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Astronomy 1010 Planetary Astronomy Fall_2016 Day-2
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Course Announcements

• Smartworks Chapter 5 Due Today
• Smartworks Chapter 6 Due Fri. Oct. 28
• Smartworks Chapter 7 Due Fri. Nov. 04
• For those concerned the last day to drop a class
  with a W (or F, FA) is THURSDAY, NOV. 3. I
  will give you a W if you decide you need to
  drop. Starting Friday Nov. 4, the system gives
  Fs.

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• Resolution smallest details that can be
  separated.
• The longer the focal length, the better the
  separation of two objects or features.
• Diffraction, or blurring of an image, sets the
  best possible resolution.
• The diffraction limit depends on the ratio of
  wavelength-to-telescope aperture.

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MATH TOOLS 6.2

• The ultimate resolution of a telescope is set by
  the diffraction limit.
• The angle subtended by the smallest resolution,
  ?, is determined by the ratio of the wavelength
  of light being studied to the aperture diameter.
• 1 arcsecond 1/3,600 of a degree.
• Human eye

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The resolution of a telescope depends on its size
and the wavelength of the light
Better resolution means smaller angle q
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The atmosphere limits the resolving power of a
ground-based telescope
Adaptive Optics can clear up most of the
distortions caused by the atmosphere
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The distortions are caused by differences in the
air above the telescope
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• Earths atmosphere degrades images.
• Astronomical seeing limit on resolution due to
  the atmosphere.
• Space-based telescopes do not have this problem.

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Turbulence

• Differences in the temperature and density of
  small portions of Earths atmosphere cause
  passing starlight to quickly change direction,
  making stars appear to twinkle.

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Once a site with good seeing is found everyone
wants to use it
Kitt Peak, Arizona
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Mauna Kea, Hawaii
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Earths atmosphere hinders astronomical research
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Adaptive Active optics

• Adaptive optical systems can overcome atmospheric
  distortion
• Active quasi-static 1 or 2 changes per minute.
• Adaptive rapid changes tens to hundreds of
  times per minute

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Back end of WIYN 3.5m telescope, photo JASmith
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• Adaptive optics can help correct for this
  atmospheric distortion.
• Earth-based image quality can compete with the
  Hubble Space Telescope in the visible.

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Image by E. Beletsky
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• Photography opened the door to modern astronomy.
• Captured images on photographic plates.
• Increased integration time comes with longer
  exposures.
• Expensive, slow, and messy.

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CCDs are much more sensitive than photographic
film
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• Electronic detectors record photons on pixels.
• Photons create a signal in the array.
• CCDs charge-coupled devices (such as digital
  cameras).

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• The electronically recorded images can greatly
  exceed photographs in quality.
• CCD astronomers detector of choice.

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Red
Green
Blue
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Red
Green
Blue