How does the Earth move in space?
The Earth moves in two ways. First, it spins, or rotates, like a spinning top. Second, while it is spinning, it orbits the Sun in an elliptical orbit.
Day and night
The Earth spins, or revolves, around its axis from west to east. The Earthís axis can be thought of as an imaginary line drawn from the North Pole down to the South Pole, around which the Earth spins. The axis always remains tilted. Earth makes one complete rotation in 23 hours and 56 minutes.
We get day and night because of the Earthís rotation around its axis. As the Earth rotates, only one half of it faces the Sun at any one time. The side that faces the Sun experiences day and the side facing away from the Sun experiences night.
The Earth can be divided into two half-spheres, or hemispheres, separated by the Equator. It takes the Earth 365.25 days to complete one orbit of the Sun. As the Earth travels round the Sun, one hemisphere is always facing more towards the Sun than the other. This is because the axis of the Earth is tilted at an angle of 23.5 degrees to the Sun.
Tides happen because both the Moon and the Sun pull the Earthís seawater towards them, by the force of their gravity. The Moon is so close to the Earth that it pulls more strongly on the side of the Earth facing it than it does on the far side of the Earth. As the Earth rotates on its axis, each part of its surface faces the Moon about once in every 24 hours. The seas at that point are most strongly attracted by the Moon. They rise up and cause a bulge of water we call high tide. Another matching bulge of water, or high tide, rises up on the other side of the Earth. The water to make the high tides comes from the areas between the two bulges. These areas experience low tides. There are two high tides and two low tides on opposite sides of the Earth every day.
The Sun is so far away that the difference in its pull on opposite sides of the Earth is very small. However, twice a month, at full moon and new moon, the Sun and the Moon pull towards Earth in line and produce tides that are higher than normal. These are called spring tides.
When the Moon is at first and last quarter, it pulls at right angles to the Sun and produces small neap tides. At these times, the effect of the Moonís gravity on the oceans is partly offset by the Sunís gravity.