Q:

# How fast does light travel?

A:

In a vacuum, the speed of light is 186,282 miles per second. This is equal to 299,792 kilometers per second or about 670,616,629 miles per hour.

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Attempts to calculate the speed of light have been going on for centuries. Aristotle believed that light traveled instantaneously, but another ancient Greek scientist, Empedocles, believed that light must take time to travel because light is capable of movement. Albert Michelson used an apparatus with a beam of light on a rapidly rotating mirror to measure the speed of light. Albert Einstein calculated that no matter how quickly an observer moves, light travels at the same speed, and that the speed of light does not vary with time or location.

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## Related Questions

• A:

Light travels at 186,282 miles per second, or approximately 670,616,629 miles per hour, in a vacuum. As of 2014, it is assumed that no object that has mass can travel at or above this speed.

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• A:

Light travels through a vacuum at 186,282 miles per second; through the Earth's atmosphere, it moves at 186,227 miles per second. The speed of light, in general, is affected by the medium through which it moves.

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• A:

According to Universe Today, light travels approximately 9.5 trillion kilometers or 5.9 trillion miles in a year. Light years are commonly referenced units, but astronomers tend to use a unit known as the parsec, equivalent roughly to 3.26 light years.