Astronomical Imaging: Overview

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Astronomical Imaging Overview

• When you think of a clear, dark night sky, what
  do you think of?
• The human visual system is fine-tuned to focus,
  detect, process ( image) the particular
  wavelengths where the Sun emits most of its
  energy
• As a result, when we look at the night sky, what
  we see is dominated by starlight
• We think stars and planets when we think of
  astronomy

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The Night Sky Orion
This is approximately what you can see with your
unaided eye when you look at Orion on a clear
night
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Magnitudes

• Magnitudes a backwards, logarithmic scale to
  measure the brightnesses of stars
• For each increase of 1 magnitude, an object is
  fainter by a factor of 2.5
• an increase of 5 magnitudes is a factor 100
  decrease in brightness
• an increase of 2.5 magnitudes is a factor 10
  decrease in brightness
• magnitude -2.5log(F/F0)
• F and F0 represent the number of photons/second
  received from an object and reference

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Magnitudes and Human Vision

• Sensitivity of human vision is limited (in large
  part) by the length of time your brain is willing
  to wait to receive and interpret the signals from
  the eye
• The brightest stars have magnitudes of about 0
• (well, OK the magnitude of Sirius is -1)
• Venus gets as bright as -4!
• The faintest stars you can see have magnitudes of
  about 5
• What if you could have your retina store up the
  signals it detects, then report them to the brain?

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You might see this when you look at Orion!
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Note that not all stars are the same color
Betelgeuse (a red supergiant)
Rigel (a blue supergiant)
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Furthermore visible light is a small part of
the whole story
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Multiwavelength astronomy

• All-sky views at various wavelengths
• Note the dominance of the Milky Way (the galaxy
  where our solar system is located)

Also note that stars are only one ingredient in a
galaxy!
Images from NASA
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The Orion NebulaStellar Nursery
The constellation of Orion (wide-field optical)
The Orion Nebula (Hubble Space Telescope optical)
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Three views of the young stars in Orion
Orion Nebula region left optical (HST) center
infrared (2MASS) right Xray (Chandra)