Note * — Chapter VIII

The Red Planet is our nearest neighbour on the further, as Venus is on the hither side. He is also in some ways the planet best situated for our observation; for while the greatest apparent diameter of his disc is considerably less than that of Venus, he does not hide close to the sun's rays like the inferior planets, but may be seen all night when in opposition.* Not all oppositions, however, are equally favourable. Under the best circumstances he may come as near to us as 35,000,000 miles; when less favourably situated, he may come no nearer than 61,000,000. This very considerable variation in his distance arises from the eccentricity of the planet's orbit, which amounts to nearly one-tenth, and, so far as we are concerned, it means that his disc is three times larger when he comes to opposition at his least distance from the sun than it is when the conditions are reversed. Under the most favourable circumstances—i.e., when opposition and perihelion† occur together, he presents, it has been calculated, a disc of the same diameter as a half sovereign held up 2,000 yards from the spectator. Periods of opposition recur at intervals of about 780 days, and at the more favourable ones the planet's brilliancy is very striking. The 1877 opposition was very notable in this respect, and in others connected with the study of Mars, and that which preceded the Crimean War was also marked by great brilliancy. Readers of Tennyson will remember how Maud