Princey Atwal, age 10, of Winnipeg, Manitoba, Canada, for his question:
HOW DOES THE EARTH MOVE?
You probably think that the fattest part of the earth is around the equator, but this isn't the case. The distance around the earth is greatest along a circle slightly to the south of the equator. The earth is a bit like a pear in its shape, which has its fattest part just below its middle. But the earth's bulge is so small that it still looks like a perfectly round ball.
Fifth ranking in size among the planets, the earth is always moving.
The earth has three motions: it spins like a top, it travels around the sun and it moves through the Milky Way galaxy with the rest of the solar system.
The earth turns around its axis which is an imaginary line that connects the North and South poles. The spinning motion makes the sun appear to move from east to west, and causes day and night on earth. The day side of the earth faces the sun, and the night side faces away.
As the earth spins eastward, some parts move from the night side to the day side. People who live in these areas see the sun come up in the east. Other parts of the earth move from the day side to the night side and persons there see the sun set in the west.
It takes 23 hours, 56 minutes and 4.09 seconds for the earth to spin around once. We call this length of time a sidereal day.
The earth moves 595 million miles around the sun in 365 days, 6 hours, nine minutes and 9.54 seconds. This length of time is called a sidereal year.
The earth's path around the sun is called the earth's orbit. The orbit lies on an imaginary flat surface that cuts through the sun. The surface is the earth's orbital plane.
The whole Milky Way galaxy spins around like a giant wheel once every 200 million years. The solar system is about three fifths of the way from the center to the edge of the galaxy. The solar system and the earth revolve around the center of the galaxy at a speed of 43,000 miles an hour.
As the earth travels around the sun, it moves at an average speed of 66,600 miles an hour.
The earth's axis does not stick straight up from the orbital plane. It tilts about 23.5 degrees from the straight up position. This tilt and the earth's motion around the sun causes the change of seasons.
The northern half of the earth tilts toward the sun in summer, for example. In winter, the northern half of the earth tilts away from the sun.