Page:In the high heavens.djvu/124

 the distance between the two bodies is double as great as it is in the August oppositions. At double the distance the planet only looks one-fourth the size, and hence the appearance of Mars, when the opposition is in February, is widely different from that which it presents in the glories of an August opposition.

We can now understand why such an opportunity as that which we are at present referring to is a rare one. In the first place an opposition of Mars occurs once every 780 days. In the second place the opposition is just as likely in the long run to take place in one month as another. Only, however, when it occurs about August is it a really favourable one. If a friend paid us a visit once every two or three years, and if his visits were impartially distributed over the various seasons, it would not be on many occasions in a lifetime that we should expect to receive him during the grouse shooting. Of somewhat similar infrequency are the favourable visits of Mars, but whenever he does happen to come into opposition about the time when the grouse are being slaughtered, then his ruddy form blazes with an unwonted splendour.

A knowledge of these facts points out that the opposition of Mars in 1892 was the best that has offered itself since 1877, and the best that will offer itself for many years to come. Hence it is that so much interest has been manifested in this phenomenon, for though it would not be true to say that Mars is our nearest neighbour in the heavenly host, yet there are circumstances which render his globe much more instructive to us than any of the other heavenly bodies.

Of course, the moon is always much closer to the earth than is Mars. Even when the moon is at its greatest