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Asked by chloewildman to Chris, Eva, Michael, Paddy, Philip on 21 Jun 2011.
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Chris Jordan answered on 21 Jun 2011:
Nice one!
Newton’s eeerrr…. first law – every keeps doing what its already doing unless something stops it. That’s not obvious here on earth itself, because if you spin something here there are things to stop it … usually friction. There’s nothing much out in space for the earth to rub against to create friction.
The earth is slowing down a very little bit (someone asked about the moon in todays chat – and as the moon goes around us some of the earth’s spin energy gets shared out with the moon by the gravity that holds the earth-moon together). Some of the earth’s energy goes in dragging weather around… there’s a bit of friction between the atmosphere and the earth but the earth is so much more massive than the atmosphere that its a minute effect.
Other things happen too – the Japanese earthquake was so big it made the whole earth jump. Japan actually moved a few metres, and the earth’s spin shifted a bit.
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Paddy Brock answered on 21 Jun 2011:
Wow! Really?! That’s cool. I didn’t realise an earthquake could affect the earth’s spin.
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Michael Wharmby answered on 21 Jun 2011:
Nice question and nice answer from Chris! The Earth is spinning as a result of left over kinetic energy (movement) from when it formed.
The Earth formed from a disk of dust, gas, rock etc. some of which went to form the other planets, some to the Earth and most(?) to the sun. That disk of dust was orbiting around the sun and as it formed into planets, that kinetic energy was transferred into making the Earth orbit the sun and making it rotate about its axis.
Correct me if I’m wrong Chris. -
Philip Denniff answered on 21 Jun 2011:
Great question chloewildam, I had never thought about it before. Now you have asked I want to know the answer, Im also glad Chris is on hand to supply it.
Comments
Eva commented on :
Hi Chrism can I ask one as well? Is it theoretically possible that the direction of the spin changes with Newton and everything? And is there any way to find out why the earth is spinning in the direction as it does?
Michael commented on :
It’d also be interesting to know if the Earth is spinning in the same direction it is rotating about the sun (ought to be if there’s anything in my answer).
Sorry you’re out Eva – hope you enjoyed yourself though. All the best with your research 🙂
Chris commented on :
Eva, Changing the direction of the spin would be like stopping it and then starting it in the opposite direction … take twice as much force. Michael has pretty well answered why we’re spinning the direction that we are … a cloud condensed to form the Sun and if this had even a bit of rotation it would show in the Sun and left over dust as it all condensed (the classic example is an ice skater spinning faster as they pull in their arms – conservation of angular momentum). As the Sun formed, left over dust formed into rotating disc, then clumps started forming to give planets and moons and asteroids. Any angular momentum has to go somewhere – and it went into the orbits of the planets and their rotation. The Sun spins anticlockwise (looking down from the N. pole of the solar system) all the planets and all except a couple of asteroids orbit anticlockwise, and nearly all moons go that way. too. There are a few exceptions Venus is gooing backwards very slowly and Uranus is lying on it’s side.
Chris commented on :
Paddy – Yes earthquakes can shift the earth spin axis and change the length of a day http://www.csmonitor.com/Science/2011/0314/Japan-earthquake-accelerated-Earth-s-rotation-study-finds
I sort of keep track of these bits of news, because one bit of astronomy means we’re really involved in keeping track of time. We need to know where to point the telescopes which means we need to know where a star is any any time of day, on any day of the year. These effects aren’t big enough to throw us in the short term, but we get a regular summary of tweaks we’ll need to take account of from Greenwich (and it’s US counterpart).
ps the earth slows down a bit in spring and speeds up in Autumn, to do with areas of sea water heating and cooling and icecaps changing (and my favourite – trees growing in spring )