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Earth factoids: Sprinkle them in your conversation

By Phil Plait
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We live on the surface of this great giant space-borne water-laden spinning rock, separated from the rest of the universe beneath a thin veil of nitrogen and oxygen molecules. Even though you’re immersed in its influence, what do you really know about the Earth?

Here are some facts about our planet for you to ponder.

• There are a lot of different ways to measure how long it takes the Earth to go around the Sun, but if you say it takes pi x 10 million seconds, you’ll only be off by a half a percent.

•  The Earth has a mass of 6,000,000,000,000,000,000,000,000 kilograms, or, if you prefer, 6 sextillion tons. In pounds, that’s actually... 0. Nothing. Mass is a measure of how much stuff an object contains, but weight is how hard gravity pulls on that mass. The Earth is in space, orbiting the sun, so it’s in freefall. It has mass, but no weight at all.

• The Earth isn’t a perfect sphere. It spins, so it’s flattened a bit at the poles. The diameter through the poles is 7,882.4 miles (12,713.6 kilometers), but it’s 7,908.8 miles (12,756.2 kilometers) through the equator. That difference of 26.4 miles or 43 kilometers is only about 0.3 percent, so really we’re pretty close to a perfect sphere.

• There is no physical place where Earth’s atmosphere stops and space begins; the air just gets thinner and thinner and eventually fades away. But we love definitions, so the official height above the Earth’s surface considered to be where space begins – called the Kármán line – is at an altitude of 100 km (62.14 miles). Anyone who gets higher than that is considered an astronaut.

• The moon’s radius is about a quarter of the Earth’s, making it the largest satellite compared to its parent planet. Charon, Pluto’s biggest moon, is about half the diameter of Pluto itself. But if you don’t consider Pluto a planet, the Earth and moon win.

• The moon is farther away from Earth than you think. As an analogy, if the Earth were a basketball, the moon would be the size of a tennis ball 24 feet (7.4 meters) away.

• The Earth’s atmosphere is only transparent to a narrow slice of the electromagnetic spectrum. What we call visible light (mostly) gets through, but most flavors of infrared, ultraviolet, X-rays and gamma-rays are stopped cold. Those last few are dangerous to life as we know it, so that works out well. But it’s not a coincidence: If our air didn’t protect us, we would have evolved differently.

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