Part 13

Our Sun is only one sun amongst many millions. Our planet is only one of eight which revolve around him.

Our Sun, with his planets and comets, comprises what is known as the solar system.

There is no reason to suppose that his is the only Solar System: there may be many millions of solar systems. For aught we know, there may be millions of systems, each containing millions of solar systems.

Let us deal first with the solar system of which we are a part.

The Sun is a globe of 866,200 miles diameter. His diameter is more than 108 times that of the Earth. His volume is 1,305,000 times the volume of the Earth. All the eight planets added together only make one-seven-hundredth part of his weight. His circumference is more than two and a-half millions of miles. He revolves upon his axis in 25 1/4 days, or at a speed of nearly 4,000 miles an hour.

This immense and magnificent globe diffuses heat and light to all the other planets.

Without the light and heat of the Sun no life would now be, or in the past have been, possible on this Earth, or any other planet of the solar system.

The eight planets of the solar system are divided into four inferior and four superior.

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.

So much for the size of the solar system. It consists of a Sun and eight planets, and the outer planet's orbit is one of 5,584 millions of miles in diameter, which it would take an express train, at 60 miles an hour, 10,560 years to cross.

But this distance is as nothing when we come to deal with the distances of the other stars from our Sun.

The distance from our Sun to the nearest fixed (?) star is more than 20 millions of millions of miles. Our express train, which crosses the diameter of the solar system in 10,560 years, would take, if it went 60 miles an hour day and night, about 40 million years to reach the nearest fixed star from the Sun.

And if we had to mark the nearest fixed star on our chart made on a scale of 1 inch to the million miles, we should find that whereas a sheet of 465 feet would take in the outermost planet of the solar system, a sheet to take in the nearest fixed star would have to be about 620 miles wide. On this sheet, as wide as from London to Inverness, the Sun would be represented by a dot three-quarters of an inch in diameter, and the Earth by a pin-prick.

But these immense distances only relate to the nearest stars. Now, the nearest stars are about four "light years" distant from us. That is to say, that light, travelling at a rate of about 182,000 miles in one second, takes four years to come from the nearest fixed star to the Earth.

But I have seen the distance from the Earth to the Great Nebula in Orion given as a thousand light years, or 250 times the distance of the fixed star above alluded to.

To reach that nebula at 60 miles an hour, an express train would have to travel for 35 millions of years multiplied by 250--that is to say, for 8,750 million years.

And yet there are millions of stars whose distances are even greater than the distance of the Great Nebula in Orion.

How many stars are there? No one can even guess. But L. Struve estimates the number of those visible to the great telescopes at 20 millions.

Twenty millions of suns. And as for the size of these suns, Sir Robert Ball says Sirius is ten times as large as our Sun; and a well-known astronomer, writing in the English Mechanic about a week ago, remarks that Alpha Orionis (Betelgeuze) has probably 700 times the light of our Sun.