# What's The Speed Of Light?

Despite what is often maintained, the speed of light isn't a constant. It only reaches its maximum 300,000 kilometres a second in a vacuum. When light passes through different media its speed slows. The slowest speed recorded is through sodium at -272 C during which the speed of light fell to 60kph – about the speed of a bicycle. Travelling through a diamond its speed is halved to 130,000 kilometres a second
Astonishingly a team of scientist at Harvard managed to bring light to a complete halt by shining it through a Bose Einstein condensate of the element rubidium.
Light is invisible to the naked eye. It is only when it hits something that it be comes visible. If light were visible it would appear as a mist between you and whatever you were viewing.
Rubidium was discovered by Robert Bunsen , 1811-99. Bunsen didn't invent the Bunsen burner. It was named after him.
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The speed of light actually refers to the speed as measured in a vacuum. This physical constant has been represented by the letter c, which stands for constant or celeritas, which is the Latin term that denotes "swiftness." In metric units, this constant c would be given by 299,792,458 meters per second (which is in effect 1,079,252,848.8 km/h). Remember that this designates the speed of every electromagnetic radiation as would be in a vacuum and not simply visible light.

Think of this speed not in terms of a measurement but rather as a definition. If converted to imperial units, you will find that the speed of light would be roughly 186,282.397 miles per second, which is 670,616,629.384 miles per hour, that is, nearly one foot per nanosecond.
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186,282.397 miles per second.
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With the speed of light, you can complete 7 revolutions of the earth in a second, to the moon in 1.25 seconds, to the sun in 8 minutes & 19 seconds & through the milky way in 100,000 years.
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The speed of light is 300,000 km per hour.
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