α _Scorpii_ (_Antares_). A fiery-red star, with a rather close, faint companion. This object being in 26° of S. declination is rarely seen with advantage in places with latitudes far north. Atmospheric disturbance usually affects the image in such degree that the smaller star is merged in the contortions of the larger. This pair is, however, interesting from the circumstance that it is frequently liable to occultation by the Moon. A night on which this double star can be distinctly seen may be regarded as an exceptional one in point of definition. It appears to have been discovered nearly half a century ago by Grant and Mitchel. _Variable Stars._—A proportion of the stars exhibit fluctuations in their visible brightness. In most cases, however, the variation is but slight, though there are instances in which the differences are considerable. The fluctuations are periodical in nature and capable of being exactly determined. But the character of the variation and the period are very dissimilar in different stars. Some are of short period, and their variations occupy a few days only; others, however, are more gradual, and twelve months or more may represent the complete cycle of their changes. These alterations of brightness generally escape the notice of casual observers of the heavens. To them the stars appear as constant in their relative magnitudes as they are in their relative positions. But a close observer of the firmament, who habitually watches and records the comparative lustre of the stars, must soon discover numerous evidences of change. He will remark certain stars which alternately grow bright and faint, and, in fact, display a regular oscillation of brilliancy. In the case of a pair of stars he may possibly notice that the superior lustre is emitted first by one and then by the other. The observation of these variables dates from a period anterior to the invention of the telescope. Nearly three centuries ago Fabricius remarked that ο Ceti (Mira) suffered a great diminution of light; for while it was of the 3rd mag. in Aug. 1596, it became invisible in the following autumn. It was re-observed by Holwarda in 1639, and as he appears to have been the first to estimate its period, some authors, including Argelander, have credited him with the discovery. The star has a period of about 331·3 days. Its variations are somewhat erratic, for at max. it is sometimes only 4th mag., while at others it is as bright as 2nd mag., and its min. are equally inconsistent.