What Are the Sizes of the Planets?

A planet is very different from a star. A star is a huge ball of hot gases that gives off heat and light. A planet is a much smaller body that shines by reflected light.

Let's start with the planet nearest to the sun and move outward. The first one is Mercury. Mercury's diameter is 2,900 miles—about the width of the Atlantic Ocean. So it's only a fraction of the earth's size.

The next planet we meet is Venus. It is very nearly the same size as the earth. Its diameter is 7,600 miles, while that of the earth is 7,913 miles. By the way, an odd fact about Venus is that it rotates backward; that is, from east to west. The next planet is our earth, and then comes Mars.

Mars shines in the sky with a reddish colour. It has a diameter of 4,200 miles, a little more than half that of the earth. Parts of its surface look like the moon, with large craters apparently formed by meteorites, but there are also giant volcanoes and valleys which prove there could be geological activity on the planet.

Jupiter, the next planet, is far away from the sun. It takes about 11.9 years to complete one orbit. Jupiter is the largest of the planets. It has a diameter of 88,700 miles, nearly 11 times the diameter of the earth.

Saturn, the next planet, is another giant. It has a diameter of 75,100 miles, which is about nine times that of the earth. An unusual thing about Saturn is the group of flat rings that circle it. These rings are made up of billions of tiny particles.

Uranus, the next planet, is much larger than the earth. It has a diameter of 32,000 miles. Uranus is tilted over on its side. Its axis is tilted over at an angle of 98 degrees. (The earth tilts at an angle of 23'/2 degrees.) Neptune, the next planet, is 30,000 miles in diameter. And finally, the last known planet, Pluto, is believed to have a diameter of about 1,865 miles. It is so far from the sun that the sun appears to it as only a bright star in the sky.