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How Many Stars?

Dark Adaptation

The Dark Adaptaion of the eye is a physiological process which occurs under reduced illumination. After a prolonged period of low illumination (a few minutes to a few hours) the eye's sensitivity to light is greatly increased and the faint-light threshold is greatly reduced.

Night (winter) before dark adaption

Dark adaptation is a much slower process than light adaptation. A brief exposure to bright light can destroy serveral hours of dark adaptation.

During dark adaptation a compound called rhodopsin is built up in the retinal rods increasing their sensitivy to light.

During the process of adjusting to low levels of illumination the cones on the retina adapt first and the rods continue to adapt for up to four hours.


During the process of adjusting to low levels of illumination the cones on the retina adapt first and the rods continue to adapt for up to four hours.

Night (winter) after dark adaption

It is not unusual to fall asleep in a room which seems totally darkened (in which you can see nothing), and to then to wake up several hours later and be able to see quite well (in the faint background light within the room). This common effect is due to the eye's dark adaptation.

A common recreational winter actvity in Canada is night-time cross country skiing. When the skies are clear and the moon is full, the experience is almost the same as skiing in full daylight.

 

Prepared by YES I Can! Science Team at McMaster University,
for the Canadian Space Agency.