Infrared basics: definitions and detectors

The response of the human eye to different wavelengths:

The eye response compared to a standard V filter:

The response of the eye when dark-adapted (scotopic) vs. when in bright light (photopic):

The response of a CCD to light of different wavelengths:

The background emission at different infrared wavelengths:

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Mid-infrared images of people. Hot areas are brighter, cold areas are darker. Note the veins in the man's arm, which are hot, and the fact that his glasses completely opaque at mid-infrared wavelengths:

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Infrared vs. optical view:

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The transmission of the atmosphere for light of different near- and mid-infrared wavelengths defines the filter bands used for IR astronomy:

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A broader view of the transmission; note that there is essentially no transmission from 25 microns to about 350 microns:

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Atmospheric transmission from the ground compared to that from a plane:

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Extinction is much lower at infrared wavelengths than optical wavelengths:

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The Orion Nebula star forming region, seen on left in visible light and on the right in infrared light:

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The galactic center in optical vs. infrared:

The Cone Nebula in optical (left) vs. infrared (right):

Next: infrared detectors and telescopes