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Wednesday, April 1, 2009

Dark Adaptation of Our Eyes

To view objects in the sky which are sometimes dim, our eyes need to first adapt to darkness.

Dark adaptation takes time. The eye’s pupil expands to its maximum diameter in seconds after the lights go out. The main cause of dark adaptation, however, is chemical and not related to the size of the pupil. Over the first 5 to 10 minutes in the dark, cone cells in our eyes reach their maximum level of dark adaptation. But over the next 20-40 minutes our eyes can gain 2 or more magnitudes of sensitivity. - MIT

This often makes a difference!

Red flashlight, however, helps protect your night vision. The rod cells in our eyes are not sensitive to red light. Rod cells are those that helped our eyes gain 2 more magnitudes of sensitivity after dark adaptation as mentioned above. The lamps in SCOB are covered with a red film, and red pocket flashlights can be purchased from Astronomy shops to read sky maps with during star gazing.

So the next time you are gazing at objects in the sky - stars, planets, nebulae... Do not blind yourself with bright flashlights from cameras. They often leave white spots in front of your eyes which hinder your own vision! :)

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