SOLAR SYSTEM

Our tiny corner of the Universe is dominated by a star we call the Sun. Trapped in the gravity of the Sun is a huge family of bodies – PLANETS, MOONS, asteroids, comets, and other smaller bodies – which hurtle with it through space. This family is our Solar System. But the effects of the Sun – its heat, gravity, light, and particles – extend far beyond Pluto, to about a quarter of the way to the next nearest star, Proxima Centauri.

THE BIRTH OF THE SOLAR SYSTEM

The Solar System is around 5 billion years old. It formed out of a huge cloud of gas and dust called the solar nebula. Under gravity, the cloud collapsed and the material formed the Sun and a disc of matter in which the planets were born.

PLANETS

Nine planets orbit the Sun at different distances. The four inner planets are balls of rock and metal. The outer planets are giant balls of gas and liquid, except for Pluto, the most distant planet, which is made of ice and rock. The time it takes a planet to orbit the Sun is its orbital period (its year). Planets also rotate (spin round) as they travel. The time it takes a planet to rotate once is its rotation period (its day).

COMPARING THE PLANETS

The planets vary widely in size. Earth is one of the smallest, just 12,756 km (7,926 miles) in diameter. More than 1,300 Earths could fit inside the largest planet, Jupiter. However, the Sun makes up 99.9 per cent of the mass of the Solar System. The planets are not upright in relation to their orbits around the Sun. The axis (the line around which it turns) of each planet is tilted at a different angle.

MOONS

A moon is a body that orbits a planet. Altogether we know of more than 120 moons in the Solar System. Earth has one, the Moon, while Jupiter has 63. Most of these moons are small asteroids captured by Jupiter’s gravity, but its largest moon Ganymede, with a diameter of 5,268 km (3,266 miles), is bigger than Mercury.

HOW OUR MOON FORMED

No one is certain how the Moon formed, but many astronomers believe that it was born when a body the size of Mars collided with the young Earth over 4 billion years ago. In the collision, material from the two bodies was heated up, became molten, and was thrown out into space. In time, the material clumped together to form the Moon.

Copyright © 2007 Dorling Kindersley

stay connected

Sign up for our free email newsletters and receive the latest advice and information on all things parenting.

Enter your email address to sign up or manage your account.

Facebook icon Twitter icon Follow Us on Pinterest

editor’s picks

highlights

Pin the Star on the Christmas Tree Game
Looking for a great Christmas game to play with your kids? Print our free Pin the Star on the Christmas Tree game for loads of family fun!

Kindergarten Readiness App Wins Gold
Our Kindergarten Readiness app won the Gold Award of Excellence in the educational category at the 2014 Communicator Awards. This valuable checklist comes with games and activities to help your child practice the essential skills she needs for kindergarten. Download the Kindergarten Readiness app today!

Top Family Movies in Theaters for the Holidays
Taking the kids to the movies is a special family treat for the holidays! Don't miss 2014's best family films in theaters from Thanksgiving through Christmas.

Find Today's Newest & Best Children's Books!
Looking for newly released books for your child? Try our new Book Finder tool to search for new books by age, type, and theme, and create reading lists for kids!