Posted on January 8, 2015
Isn't that literally what day means? (Day = 24 hour period corresponding to one rotation of the earth on its axis.)
And you would be exactly right. I suppose today is the day to actually acknowledge that rotation!
You probably know that most people in the far past thought of the Earth as the one stable, unmoving thing in the cosmos. You know, the thing that is rock solid and firm beneath our feet! Everything else—Moon, Sun, stars, nebulae, and planets—seemed to be moving around Earth. Most of these things seemed to slowly wheel across our skies at one consistent pace...But the consistent pace was of course the speed at which the Earth was spinning!
|Sun up and sunset are of course |
REALLY just the world spinning.
Ditto "day" and "night."
(As it turns out, everything in the universe is rushing around at really amazing speeds. Earth is not only spinning on its axis, it is also orbiting the Sun. Our solar system is part of the Milky Way Galaxy's giant pinwheel rotation, and the galaxy is rushing away from all the other galaxies. A lot of motion in this cosmic ocean!)
Here are some questions to consider:
- What would happen if the Earth's rotation were to gradually slow down?
- What would the planet be like if the Earth didn't rotate on its axis but still orbited around the Sun?
- The Earth could (probably) never ever suddenly stop rotating on its axis, but what would happen if it did?
Think about that for a while....
Here are some answers:
- If the Earth's rotation (spinning) were to gradually slow down, the day would get longer and longer.
Actually, the Earth's rotation IS gradually slowing down! The day is longer now than it was in the distant past! Not necessarily a lot longer, though. Scientists have discovered that a modern day is 1.7 thousandths of a second longer than a day a century ago.
The Earth's rotation is gradually slowing because of the tidal friction caused by the Moon pulling on the Earth, kind of dragging at it. How it works is that the orbital momentum is being transferred from the Earth to the Moon, and the Moon is slowly receding from the Earth (about four centimeters a year).
- If the Earth didn't rotate on its axis, a day would be as long as a year. Let's say the Earth slowed its rotation all the way down to a standstill. If that happened, the oceans would migrate to the poles, and the Earth would have one huge equatorial mega-continent and two polar oceans. Take a peek at this website for more on this scenario.
- If the Earth was to suddenly stop spinning, everything else would still be in motion at the same 1100 mile per hour speed that the Earth now rotates. So everything on the surface – including all the water and air and animals and people – would be suddenly moving SIDEWAYS to Earth, and the land surface would be scrubbed clean of anything not attached to bedrock.
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