Mt. Vernon Register-News

April 23, 2013

Slate: 15 facts about our planet

By Phil Plait

— It's easy to take Earth for granted, since we see it every day. It becomes — it is — part of life's background.


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


2. The Earth has a volume of about one trillion cubic kilometers. Can you picture a cube 1000 meters high, 1000 meters deep, 1000 meters across? Now picture a trillion of them. That's the Earth.


3. 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.

4. The Earth isn't a perfect sphere. It spins, so it's a flattened at the poles a little bit. The diameter through the poles is 12,713.6 kilometers (7882.4 miles), but it's 12,756.2 kilometers (7908.8 miles) through the equator. That difference of 43 kilometers is only about 0.3 percent, though, so really we're pretty close to a perfect sphere.


6. 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. Anyone who gets higher than that is considered an astronaut.

7. The Moon's radius is about 1/4 that 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. So if you don't consider Pluto a planet, the Earth and Moon win.



10. The Earth is warming up. It's a fact. Deal with it.

11. Fewer than 200 impact craters have been cataloged on Earth. The Moon has billions. We'd have just as many, but our air and water erode them over time, erasing them. Old craters on the Earth are hundreds of millions of years old; on the Moon those would be considered young.

12. An asteroid, 2010 TK7, shares an orbit with the Earth. It's about 300 meters (1000 feet) across, and never gets close enough to us to be a danger.


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:




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."