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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

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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 = -2.5*log(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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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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Gamma Ray

X-ray

Visible

Infrared

Radio Waves

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 Nebula:Stellar 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)


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