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April 22, 2013

Slate: 15 facts about our planet

(Continued)

13. The Earth orbits the Sun on an ellipse. The shape changes slightly over time due to the influence of the other planets, but on average the closest we get to the Sun (perihelion) is about 147.1 million kilometers (91.3 million miles) and the farthest (aphelion) about 152.1 million kilometers (94.3 million miles). That difference is only about 3 percent, which by eye is very nearly a perfect circle.

14. If you took all the water on Earth and collected it into a single drop, it would be just less than 1400 kilometers (860 miles) across.

15. The Earth's atmosphere weighs 5 quintillion kilograms, or 5000 trillion tons! You can do this math yourself: Weight is equal to pressure times area. Atmospheric pressure on the Earth's surface is about 1 kilogram per square centimeter. Multiply that by the number of square centimeters on the Earth's surface and you get the weight of all that air. Hint: The area of a sphere is 4 x pie x radius squared. [Note: Yes, I know kilograms are a mass and not a weight.]

And a bonus, because it's important:

16. The Earth is the only place in the entire Universe where we know that life exists. But that won't be true forever.

To us, our Earth seems huge, solid, tailor-made for us, and permanent. But that is just one perspective, born of living on its surface. From a different perspective, none of those things is true. Seen from space, it looks much less unbreakable. Seen from deep space it shrinks to nothing more than a dot, barely visible in the reflected light of the Sun. From another star, even seeing our planet at all would be a colossal task. We are, after a monumental effort spanning decades, only just now finding other planets orbiting other stars.

Is any like Earth? Almost certainly, and in fact there may be billions of planets like ours orbiting alien stars. But while they are like ours, they aren't ours. As with any individual, our world is unique, and precious, and wonderful. Let's keep it that way.

Phil Plait, the creator of Bad Astronomy, is author of "Bad Astronomy: Misconceptions and Misuses Revealed, from Astrology to the Moon Landing 'Hoax' " and "Death from the Skies! These Are the Ways the Universe Will End."

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