Why lights flicker from a distance

A distant street-lamp, or indeed the stars in the sky, meet this criterion. If, however, we move nearer to a street-lamp, it will twinkle less and less as we approach; eventually the scintillation ceases altogether when the angular diameter of the lamp - its size as perceived by the eye - has grown to the extent that it no longer approximates to a "dot" of light.

Please update your payment details to keep enjoying your Irish Times subscription. Stand back to see the street lights scintillate Wed, Oct 20, , Most Viewed. Watch More Videos. Coronavirus Explore our guides to help you through the pandemic. Latest News. Dean Smith set to be appointed Norwich City manager Luxembourg 0 Republic of Ireland 3: Ireland player ratings West must be on guard for war with Russia, says head of British armed forces When they sweep across your eye, you see a flickering.

Try this: look at distant flickering lights, then cross your eyes so you see double. Look carefully at the pairs of flickering distant lights. This happens when the diffraction fringes projected onto your face are shorter than the distance between your eyes. As the parallel shadow bars rake across your eyes, one eye is seeing one pattern while your other eye sees a slightly different pattern. This same crosseye trick works for twinkling stars.

Perhaps the word obstruction could have been improved on. The twinkling or scintillation of stars is the result of the light rays being bent refracted and dispersed from their direct path by passing through air of varying density. The twinkling of stars is strongest when the sky is clear and it is windy, at least at higher altitudes.

Stars nearer the horizon twinkle more than those overhead because there is more atmosphere through which the light must pass. Read the Digital Magazine.

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