Further observations have shown that this irregularity of their path is only apparent, and that, like our own Earth, they really revolve round the Sun. To the five first observed--Mercury, Venus, Mars, Jupiter, and Saturn--two large ones, Uranus and Neptune, and a group of minor bodies, have since been added. The following two diagrams give the relative orbits of the Planets. [Illustration: Fig. 51.--Orbits of the inner Planets.] MERCURY It is possible, perhaps probable, that there may be an inner Planet, but, so far as we know for certain, Mercury is the one nearest to the Sun, its average distance being 36,000,000 miles. It is much smaller than the Earth, its weight being only about 1/24th of ours. Mercury is a shy though beautiful object, for being so near the Sun it is not easily visible; it may, however, generally be seen at some time or other during the year as a morning or evening star. [Illustration: Fig. 52.--Relative distances of the Planets from the Sun.] VENUS The true morning or evening star, however, is Venus--the peerless and capricious Venus. Venus, perhaps, "has not been noticed, not been thought of, for many months. It is a beautifully clear evening; the sun has just set. The lover of nature turns to admire the sunset, as every lover of nature will. In the golden glory of the west a beauteous gem is seen to glisten; it is the evening star, the planet Venus. A week or two later another beautiful sunset is seen, and now the planet is no longer a glistening point low down; it has risen high above the horizon, and continues a brilliant object long after the shades of night have descended. Again a little longer and Venus has gained its full brilliancy and splendour. All the heavenly host--even Sirius and Jupiter--must pale before the splendid lustre of Venus, the unrivalled queen of the firmament."[67] 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]