There is another lunar feature to be mentioned somewhat akin to the foregoing in appearance but apparently, however, owing its origin to a different cause. I refer to the systems of bright streaks which, especially at or near the time of full Moon, are seen to radiate from several of the largest craters, and in particular from Tycho, Copernicus, Kepler and Aristarchus. These bright streaks extend in many cases far beyond what may fairly be considered as the neighbourhood of the craters from which they start, traversing distant mountains, valleys and other craters in a way which renders it very difficult to assign an explanation of their origin. There are 13 areas on the Moon, which used to be regarded as “seas,” one of them, however, bearing the name of “_Oceanus Procellarum_,” the “Ocean of Storms”; but besides these there are several bays, termed in Latin _Sinus_, of which the most important is the _Sinus Iridum_ or the “Bay of Rainbows,” a beautiful spot on the northern border of the _Mare Imbrium_, and best seen when the Moon is between 9 and 10 days old. The summits of the semi-circular range of rocks which enclose the bay are then strongly illuminated and a greenish shadow marks the valley at its base. By the way, it is worth mentioning that not a few of the lunar seas, so-called, seem to be pervaded by a greenish hue, though no particular explanation of this fact is forthcoming. Much controversy has ranged round the question whether or not the Moon has an atmosphere. Without doubt the preponderance of opinion is on the negative side, though it must be admitted that some observers of eminence have suggested that there are indeed traces of an atmosphere to be had, but that it is extremely attenuated and of no great extent, otherwise it must render its presence discoverable by optical phenomena which it is certain cannot be detected. A brief reference may here be made to a curious phenomenon sometimes seen in connection with occultations of stars by the Moon. Premising that an “occultation” is the disappearance of a star behind the solid body of the Moon by reason of the forward movement of the Moon in her orbit, it must be stated that though generally the Moon extinguishes the star’s light instantaneously, yet this does not invariably happen, for sometimes the star seems to hang upon the Moon’s limb as if reluctant to disappear. No very clear or satisfactory explanation of this phenomenon has yet been given; the existence of a lunar atmosphere would be an explanation, and accordingly this anomalous appearance, seen on occasions, has been advanced in support of the theory that a lunar atmosphere does exist; but, nevertheless, astronomers do not accept that idea.