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Stephen James O'Meara's secret sky: Vanishing acts, part 1

July 2008: With assistance from your naked eyes, here's a few magic tricks in the sky.
In 1918, Harry Houdini performed his greatest feat when he made Jennie the Elephant vanish in the middle of New York's Hippodrome Theater. But that trick is peanuts compared to your natural ability to make stars vanish from the sky. Yes, the magic is in you. All you need is a clear night, transparent skies, and the ability to look straight at a star without averting your gaze. It's trickier than you think.

To see faint objects, stargazers have learned to avert their gaze. Doing so places a star's image on the eye's night-sensitive rod cells, which line the periphery of the retina. Using averted vision at night is a basic human instinct. We rely on it to detect shape and movement in low-light situations. Looking at anything other than the Moon and the bright planets with a direct gaze after sunset is almost taboo. Averted vision is one of the important principles of visual perception in amateur astronomy.

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