The Planets and their Movements Aristotle was an ancient Greek who lived about 300B.C. and he believed that the Earth was the center of the Universe and that everything else in the sky revolved around Earth. People believed this for more than 1000 years.

In 1543 a Polish astronomer Copernicus stated that the planets, including Earth, orbited the Sun not the Earth.

In 1610 Galileo used one of the first telescopes and discovered the moons rotating around Jupiter. Since he saw the moons orbit Jupiter, he proved that all bodies do not orbit Earth.

In the early 1600's a German astronomer, Johannes Kepler, proposed three laws which described the movement of the planets.

1-the orbit of each planet is an eclipse. The eclipse is an oval that has two foci points. The length of a line drawn from one focus to the other is always the same. The Sun is the focus at one end of the orbit of a planet, there is another at the other end.
2-a planet moves faster closer to the Sun
3-The size of a planet's orbit is related to its period, or the length of time it takes to orbit the Sun.

The Universe
When we talk about the Universe, we mean everything that exists. The Earth is part of the Universe. We are located in a galaxy called the Milky Way and we are one of nine planets that orbit the sun. Everything you see with your naked eyes when you look out into the night sky is part of the Milky. There are billions of starts and galaxies in the Milky Way Galaxy. It would take you 100,00 years to travel across the Milky Way Galaxy.

Gravitational Pull
Gravitation is on kind of attraction of one body for another. Because of this gravitation, the earth attracts all another a objects. A planet's gravitational attraction for objects is its force of gravity. The weight of any object on Earth or any other planet is the force that gravity exerts upon the object. Weight is not the same as mass. Mass is the amount of material used to make up an object.
 

Earth is the third planet from the Sun and the only planet that supports life as we know it.

Jupiter is a gigantic planet. It is 11 times larger in diameter that the earth. Jupiter is considered a near- star because its core gives off an enormous amount of heat. The surface of Jupiter is not solid like the Earth. Under Jupiter's clouds may be a liquid hydrogen ocean that is 70,000 kilometers deep. In 1979 the Voyager spacecraft passed close enough to Jupiter to learn valuable information. Jupiter has two moons and a faint ring. There is a turbulent storm that has been occurring on Jupiter for more that 150 years.
 

Earth's Moon
The moon has no air or water on it. Due to this the surface of the moon has not been eroded or changed for billions of years.

 The moon circles the earth once every 29.5 days. When the moon is in the opposite part of the sky from the sun, the side of the moon that faces the earth is completely lighted and we see a full moon. When most but not all the lighted side of the moon is visible, we see a gibbous moon. When only a sliver of the moon is visible, people call it a crescent moon. When the moon is very close to the Sun in the sky only the of the moon that faces away from us is lighted. The side that faces us is dark. This is called a new moon.

Mars has a thin carbon dioxide atmosphere and two small moons which rotate around it. Mars has seasons like earth It is much colder on Mars than on Earth.

Saturn is known as the ringed planet. It is smaller than Jupiter and like Jupiter is covered with clouds. It is made almost entirely of hydrogen and helium. Like Jupiter Saturn gives off more energy than it receives from the sun. The rings around Saturn are actually thousands of ringlets made of slightly different material. The rings are chunks of rock covered in ice. Saturn has five moons.

Pluto wasn't discovered until 1930 and is the farthest planet away from the sun. Pluto has one moon. Pluto is very small compared to the other planets.

Uranus has five moons and a set of nine rings around it.

The Sun
Scientists calculate that the interior of the sun is 15,000,000 degrees Celsius. The surface is much cooler than the interior. The darker spots you see are sunspots which have a temperature of 4,500 degrees Celsius. Most Sunspots are larger than the earth. Above the Sun's surface is a thin layer of gas called the corona. The corona's temperature is 2,000,000 degrees Celsius.

The sunspots follow a fairly regular cycle. The occur due to solar flares or eruptions from the surface of the sun which spews particles and radiation out into the universe. Some of the reaches earth and causes changes in telephone lines, electric lines, and satellite reception.

The propulsion of the gas from the rocket's engines is met by an opposite and equal force which pushes the rocket forward.
 

Newton's Laws of Motion
English scientist Isaac Newton developed three laws about motion. These laws helped explain Kepler's ideas of planetary motion.
law 1 objects tend to continue as they have been. If they are at rest, they stay at rest. If they are moving they will continue in the same direction unless something changes the motion. The Voyager spacecraft was launched from Earth and kept moving toward Jupiter without an additional power. There is very little in space to change its motion.
law 2 When a force acts upon an object, the object will change speed, direction, or both.
law 3 "for every action there is an opposite and equal reaction" which more simply stated means that when you push on any object it will push back at you with the same force. This explains how rockets and jet propulsion works. Gas is forced out of the back of the rocket and jet engines by a force pushing backward. A force of equal strength in the opposite direction, therefore, pushes the jet or rocket forward.

Learn more about Sir Isaac Newton