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 owe we 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 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 on the constellation of Hercules at the rate of at least 20,000 miles an hour, or over 300 miles a minute.[68]
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 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.