Did you know you can use light as a yardstick? Charae and Professor B calculate how long it takes light to get from the Sun to the Earth, and discover that they are sitting only one light-nanosecond from each other! [2:00m]

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What’s the facts?

The speed of light is 300,000 kilometers per second, or 186,000 miles per second, and it’s a constant in the Universe. This makes it handy for switching between measures of time and measures of distance. For example, we can calculate how long it takes for light from the Sun to reach us, by dividing the distance between the Sun and the Earth – 150 million kilometers (93 million miles) – by the speed of light; it’s a bit over 8 minutes. We can also measure distances by multiplying the speed of light by a time. Astronomers commonly use the light-year, the distance light travels in a year, to measure the distances to stars. One light-year is equal to 9.5 million million kilometers, or 6,000,000,000,000 miles – whew! For distances closer to home, a light-nanosecond – which is about a foot – is a little more useful.