The Solar System and Beyond page 2 and 3

As the distance between objects increases, the force of gravity between them decreases. If Earth were farther away from the sun, the force of gravity between Earth and the sun would be less.

The sun’s gravity keeps the planets and other objects in the solar system in orbit around the sun. An orbit is the path one object takes around another object. If it were not for the sun’s gravity, planets and other objects in the solar system would speed off into outer space. The gravity of a planet keeps its moons in orbit around it.

The Planets

Eight planets revolve around the sun. Each planet is a different distance from the sun. This diagram shows the planets’ distances from the sun. The sizes of the planets are not shown to scale.

Each planet’s orbit around the sun is a flattened circle called an ellipse. Each planet takes a different and predictable amount of time to complete one trip around the sun. One trip around the sun is called a revolution. The time it takes for a planet to complete one revolution around the sun is a planet’s year. The closer a planet is to the sun, the shorter the planet’s year is.

The planets are much smaller than the sun. The largest planet in the solar system is Jupiter. But Jupiter’s diameter is only about one-ninth the diameter of the sun.

Important Facts About the Planets

·         One way to remember the order of the planets:

MY VERY EXCELLENT MOTHER JUST SERVED US NUGGETS

MY= Mercury

VERY= Venus

EXCELLENT= Earth

MOTHER= Mars

JUST= Jupiter

SERVED= Saturn

US= Uranus

NUGGETS= Neptune

·         EARTH is the THIRD planet from the sun

·         THE OUTER PLANETS- are made of gases and Liquids-They are Jupiter, Saturn, Uranus, and Neptune

·         THE INNER PLANETS- are made of rocky surfaces- They are Mercury, Venus, Earth, and Mars

·         The farthest planet is the hardest to see from Earth even with a telescope.

Asteroid Belt

There is a large space between the orbit of Mars and the orbit of the next planet, Jupiter. In this space is a belt of small and large rocks called asteroids.

Important Facts

·         ASTEROIDS are made of rock and metal materials and they are sometimes called “MINOR PLANETS”

·         COMETS are frozen mass of rocky material. They form a bright cloud and have long tails as they orbit around the Sun.

·         COMETS are SMALLER than the planets

·         METEORS are also called “SHOOTING STARS”

Pluto

For nearly 80 years, Pluto was considered to be the ninth planet of the solar system. It is very far away from Earth, and no space probes have visited it. In 2006, scientists decided that for an object to be a planet, it had to be in a clear orbit around a star. Because Pluto is not in a clear orbit around the sun, scientists reclassified it as a “dwarf planet”