The nearest point of approach does not necessarily occur on the actual date of the opposition. In 1907 Mars was in perigee, as it is termed, seven days after the opposition; while in 1909, perigee was before opposition.
The diagram showing the positions and movements of the planets during the period covered by the outward voyage of the Areonal is sufficiently explained by the notes printed thereon. It may, however, be pointed out that though the orbits of the planets are all elliptical, especially those of Mercury and Mars, they are so nearly true circles that, when reduced to the scale of these diagrams, they practically become circles. The exaggerated ellipses so often found in astronomical books are very misleading. The orbits of Mercury and Mars have an appearance of ellipticity because the sun does not occupy the central point in the diagram.
The view of the moon is photographed from a large coloured drawing by the author, which occupied many months in preparation and execution. It shows all the principal formations seen through the telescope as the moon passes through its various phases, but it must be understood that the formations can never all be seen at one view as shown in this picture. As the sun rises on any particular formation the details are gradually revealed by the long shadows cast by the more elevated portions when the sun is low down in the lunar sky. As the sun rises higher and higher the shadows grow shorter and shorter, and when the sun is vertically over the formation the shadows entirely disappear; all details are thus rendered invisible.
When the moon is full the sun is practically vertical over the whole lunar surface, so the only details then seen are those which are vaguely brought out by differences in tint.
The bright ray-streaks are only suggested in the picture, because, if shown complete, they would have the same effect as upon the moon, viz. they would entirely obliterate all the formations over which they passed.
The Key Map indicates the principal lunar formations, and includes the names of those mentioned in the book.
The last two plates in the book are from drawings made at the telescope (a 12-inch Calver reflector) by the Rev. T. E. R. Phillips. The opposition of 1909 was not favourable for the observation of Martian details from England; for although the planet was near to us, it was too low down in the sky; and many of the nights were either cloudy or misty.
THE SUN, MOON, AND PLANETS