Influence of the Sun and the Moon

The Sun and the Moon both have their influences on the earth. Sometimes they cooperate and sometimes they counteract each other. Such influences are: gravity, the heat of the sun, sunlight and our chronology.

Chronology:
The earth rotates with a speed of 65,000 mph(105,000 kph) in an elliptic (oval) orbit around the sun. One rotation around the sun takes 365,42 days. The Western calendar year is 365 days long. Therefore every four years the Western calendar adds an extra day (a leap year) to compensate this. This happens at February 29. In one orbit around the sun the earth 'travels' 584,018,150 miles (939,886,400 km). The distance from the earth to the sun is at the closest point 91,402,300 miles (147,097,800 km) on January 3. The distance at the farthest point is 94,509,400 miles (152,098,200 km) on July 4.
The moon rotates around the earth in 273,3 days. But because the earth also spins, there are 29,53 days between two Full Moons. It is Full Moon when we see all of its bright side lighted by the sun. When the moon is completely dark, it is New Moon. The classification in months is based on the time it takes for the moon to go through all its four phases.
The earth also rotates around its own axis. In 24 hours the earth spins around its axis from west to east. One spin of the earth around its own axis is a day. Different places on the earth's surface move at different speeds. Places near the Poles barely move at all, while those on the equator (a line midway between the Poles) zoom around at more than 1,000 mph(1,600 kph).

Light:
Because the earth rotates in 24 hours from west to east, you see the sun rising everyday in the east and sinking in the west. The earth's axis is not quite at right angles to the sun, but tilts over at an angle of 23,5º , this is the angle of inclination. Through the tilt of the earth's axis, daylight varies throughout the year. It varies the least at the equator and the most at the Poles. Therefore, it is never completely dark at the Poles in summer nor is it is ever completely light in winter.
The cycle of New Moon to Full Moon and back causes that at night a part of the sunlight gets reflected by the moon to the earth's surface. Because of this it gets less dark.

The Heat of the Sun:
Besides light, the sun also produces heat waves. From the total radiation of heat of the sun, 47 percent reaches the earth's surface. The other 53 percent gets absorbed or reflected in different ways: 23 percent gets reflected by clouds, 16 percent gets absorbed by steam, dust and gases in the air, 7 percent gets diffused and spread by the atmosphere, 4 percent gets reflected by land and oceans and 3 percent gets absorbed by clouds.

 The fate of solar radiation Only 47 percent of solar radiation reaches the ground. The remaining 53 percent is absorbed or reflected in various ways on its way down. Image by: Roy Flookes, Dorling Kindersley
 Seasonal change It is the Earth's tilted axis that produces seasonal weather and gives us days of different length. If the Earth was at right angles to the Sun, day and night would always be equal length, and there would only be one season throughout the whole year. Image by: Roy Flookes and Dave Donkin, Dorling Kindersley

Because the earth's axis is not quite at right angles to the sun, the four seasons exist: spring, summer, autumn and winter. In summer the sun shines longer and is high in the sky and the sunrays shine more directly at the earth's surface. That's why the weather is warmer then. In winter it is just the opposite. The sun shines shorter and the sunrays reach the earth's surface at a wider angle, which causes temperatures to drop.

Gravity:
Gravity causes the earth to move around the sun. It is an invisible force that is still not completely understood by science. This phenomenon not only causes the earth to keep moving around the sun, but also to keep the moon rotating around the earth and it makes things fall to the ground. All matter, even the smallest object, has a gravitational force. The heavier the object, the stronger its gravitational force.

The sun is far away but it's very heavy and has a big gravitational force with respect to the earth. Because of the speed, the earth has the tendency to fly away from the sun. The gravity of the sun stops this, so that the earth stays in its orbit. This also happens when you swing around an object on a rope. You feel the power by which you keep the item in its orbit as long as you keep swinging the rope. When you let it go, the item shoots outwards.

 How tides are formed Roughly every 12 hours, the oceans on each side of the globe rise a little and then fall back. These tides are caused by the varying gravitational pull between the spinning Earth and the Moon and the Sun. Image by: Dave Donkin, Dorling Kindersley
The earth is also a big and heavy 'object' and also has a big gravity. This is why we keep staying on the ground and that everything you let go, falls to the ground. The moon spins around the earth and keeps moving by the attraction of the earth in the same way as the earth keeps moving around the sun. But the moon also has its attraction to the earth. We can see this every day on the beach when we witness the movements of high tide and low tide. Because the sun and the moon exert their gravitational influences on the earth, the earth gets stretched into a slight oval. The solid part of the earth (the crust) is difficult to stretch. With the water in the oceans it gets easier, because it's fluid. By this the oceans rise and fall at both sides of the earth and you get high tide and low tide. When the sun, the earth and the moon line up, these forces get stronger and you get spring tide (especially high tide). When the sun is at right angles with the moon, then these forces counteract and you have neap tides (especially low tide).

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