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Millionth of an inch

Date: Wed Oct 23 14:50:18 1996
Posted by: Alison Hines
Grade level: 4-6
School/Organization: Mahopac Middle School
City: mahopac State/Province: NY
Country: US
Area of science: Environment/Ecology


If the earth moved closer to the sun by a millionth of an inch, would the earth burn up? My science teacher told us that. How much closer to the sun would we have to get for this happen?

Well, I'm not sure what you're teacher meant by that, but I assure you, the Earth could move lots closer to the Sun without burning up!

The Earth orbits the Sun in a path shaped like an ellipse, or oval. That means that sometimes the Earth is closer to the Sun than other times. In January the Earth is closest to the Sun: it's about 147 million kilometers away (a kilometer is a little more than half a mile). In July it is at a distance of 152 million kilometers, which is a difference of five million kilometers (about 3 million miles). That difference only affects our temperature a little tiny bit, and it's a lot more than one-millionth of an inch!

If you moved the Earth to the place where Venus is around the Sun, (Venus is about 100 million kilometers from the Sun) the Earth's temperature would go up about 40 degrees Centigrade. That would be very bad for us, but it would not burn up the Earth.
[Note added January 21, 1998: I originally had that the Earth's temp would go up by 20 degrees, but recently redid this calculation and got 40. Details can be found on my Bad Astronomy page about the seasons.

Maybe your teacher meant that if the Earth were really closer to the Sun it would burn up. That is certainly true, but is not very likely to happen!

One more thing-- sometime in the future, the Sun will probably swell up into a red giant: a giant star whose diameter can be over 300 million kilometers across! Some people think that the Earth will be evaporated when that happens. But don't worry-- it won't happen for another 5 to 10 billion years! Hopefully by then we'll move to another planet, or figure out a way to stop the Sun from expanding. Who knows?

©2008 Phil Plait. All Rights Reserved.

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