The inferior planets are Mercury, Venus, the Earth, and Mars. The superior are Jupiter, Saturn, Uranus, and Neptune.
The diameters of the smaller planets are as follow: Mercury, 3,008 miles; Mars, 5,000 miles; Venus, 7,480 miles; the Earth, 7,926 miles.
The diameters of the large planets are: Jupiter, 88,439 miles; Saturn, 75,036 miles; Neptune, 37,205 miles; Uranus, 30,875 miles.
The volume of Jupiter is 1,389 times, of Saturn 848 times, of Neptune 103 times, and of Uranus 59 times the volume of the Earth.
The mean distances from the Sun are: Mercury, 36 million miles; Venus, 67 million miles; the Earth, 93 million miles; Mars, 141 million miles; Jupiter, 483 million miles; Saturn, 886 million miles; Uranus, 1,782 million miles; Neptune, 2,792 million miles.
To give an idea of the meaning of these distances, I may say that a train travelling night and day at 60 miles an hour would take quite 176 years to come from the Sun to the Earth.
The same train, at the same speed, would be 5,280 years in travelling from the Sun to Neptune.
Reckoning that Neptune is the outermost planet of the solar system, that system would have a diameter of 5,584 millions of miles.
If we made a chart of the solar system on a scale of 1 inch to a million miles, we should need a sheet of paper 465 feet 4 inches wide. On this sheet the Sun would have a diameter of less than 1 inch, and the Earth would be about the size of a pin-prick.
If an express train, going at 60 miles an hour, had to travel round the Earth's orbit, it would be more than 1,000 years on the journey. If the Earth moved no faster, our winter would last more than 250 years. But in the solar system the speeds are as wonderful as the sizes. The Earth turns upon its axis at the rate of 1,000 miles an hour, and travels in its orbit round the Sun at the rate of more than 1,000 miles a minute, or 66,000 miles an hour.