Why is the area of space outside of Earth dark when part of the planet is daytime?
In: Physics
The first thing to understand: Light will always travel in straight lines unless it is reflected, bent or scattered.
The second thing to understand: Space is empty, so there is nothing for the light waves to interact with and so we observe it as black.
When we look at an object, what we are actually observing are light waves reflecting off of the object. The color of an object is determined by what wavelengths of light an object reflects and absorbs. A white object reflects almost all of the wavelengths of light, a red object reflects red wavelengths of light and absorbs the other wavelengths, a black object absorbs almost the wavelengths of light.
When sunlight hits the atmosphere on a nice clear day, blue wavelengths of light are scattered by all the gases and air molecules in the atmosphere giving the sky the appearance of being blue. The atmosphere gets thinner and thinner the higher it goes and eventually the density of gases and air molecules is so low that the light is no longer being reflected, bent or scattered. This ’empty’ space therefore appears black as there is nothing for the light waves to interact with.
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