Sirius and Jupiter - must pale before the splendid lustre of Venus, the unrivalled queen of the firmament."1

Venus is about as large as our Earth, and when at her brightest outshines about fifty times the most brilliant star. Yet, like all the other planets, she glows only with the reflected light of the Sun, and consequently passes through phases like those of the Moon, though we cannot see them with the naked eye. To Venus also we owe mainly the power of determining the distance, and consequently the magnitude, of the Sun.

THE EARTH

Our own Earth has formed the subject of previous chapters. I will now, therefore, only call attention to her movements, in which, of course, though unconsciously, we participate. In the first place, the Earth revolves on her axis in 24 hours. Her circumference at the tropics is 24,000 miles. Hence a person at the tropics is moving in this respect at the rate of 1 Ball, Story of the Heavens.

1000 miles an hour, or over 16 miles a minute.

But more than this, astronomers have ascertained that the whole solar system is engaged in a great voyage through space, moving towards a point in the constellation of Hercules at the rate of at least 20,000 miles an hour, or over 300 miles a minute.1

But even more again, we revolve annually round the Sun in a mighty orbit 580,000,000 miles in circumference. In this respect we are moving at the rate of no less than 60,000 miles an hour, or 1000 miles a minute-a rate far exceeding of course, in fact by some 100 times, that of a cannon ball.

How few of us know, how little we any of us realise, that we are rushing through space with such enormous velocity.

MARS

To the naked eye Mars appears like a ruddy star of the first magnitude. It has two satellites, which have been happily named

1 Some authorities estimate it even higher.

Phobos and Deimos-Fear and Dismay. It is little more than half as large as the Earth, and, though generally far more distant, it sometimes approaches us within 35,000,000 miles. This has enabled us to study its physical structure. It seems very probable that there is water in Mars, and the two poles are tipped with white, as if capped by ice and snow. It presents also a series of remarkable parallel lines, the true nature of which is not yet understood.

THE MINOR PLANETS

A glance at Figs. 51 and 52 will show that the distances of the Planets from the Sun follow a certain rule.

If we take the numbers 0, 3, 6, 12, 24, 48, 96, each one (after the second) the double of that preceding, and add four to each, we have the series

For this sequence, which was first noticed by Bode, and is known as Bode's law, no explanation can yet be given. It was of course at once observed that between Mars and Jupiter one place is vacant, and it has now been ascertained that this is occupied by a zone of Minor Planets, the first of which was discovered by Piazzi on January 1, 1801, a worthy prelude to the succession of scientific discoveries which form the glory of our century. At present over 300 are known, but certainly these are merely the larger among an immense number, some of them doubtless mere dust.

JUPITER

Beyond the Minor Planets we come to the stupendous Jupiter, containing 300 times the mass, and being 1200 times the size of our Earth-larger indeed than all the other planets put together. It is probably not solid, and from its great size still retains a large portion of the original heat, if we may use such an expression. Jupiter usually shows a number of belts, supposed to be due to clouds floating

over the surface, which have a tendency to arrange themselves in belts or bands, owing to the rotation of the planet.

Jupiter
Jupiter has

four moons or satellites.

SATURN

Next to Jupiter in size, as in position, comes Saturn, which, though far inferior in

dimensions, is much superior in beauty. To the naked eye Saturn appears as a brilliant star, but when Galileo first saw it through a telescope it appeared to him to be composed of three bodies in a line, a central globe with a small one on each side. Huyghens in 1655 first showed that in reality Saturn was surrounded by a series of rings (see Fig. 53).