What Is Twilight?
What Is Twilight? Twilight is the faint light which appears a little before sunrise and again after sunset before it gets really dark. On the Moon there is no twilight....
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What Is a Lucifer?
What Is a Lucifer? “Lucifer” is a slang name for a match, made usually of a splint of wood tipped with an inflammable substance which ignites when the match is struck...
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Why Do Aircraft Sometimes Leave Vapor Trails?
Why Do Aircraft Sometimes Leave Vapor Trails? Vapor trails form in the sky because the water in the exhaust of aircraft engines condenses when it meets the cool air....
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Who Was the Last Man to Discover a Planet?
Who Was the Last Man to Discover a Planet? Clyde Tombaugh, a young American research student, made the last discovery of a planet while working in 1930 at the Lowell...
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How Far Can You See?
How Far Can You See? How far the human eye can see depends on how many particles of light, or photons, a distant object emits. The farthest object visible with the...
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