One other point and we have disposed of eclipses of the Moon. The shadow which we see creeping over the Moon during an eclipse is, as we know, the shadow cast by the Earth. If we notice it attentively we shall see that its outline is curved, and that it is in fact a complete segment of a circle. Moreover that the circularity of this shadow is maintained from first to last so far as we are able to follow it. What is this, then, but a proof of the rotundity of the earth? This shape of the Earth’s shadow on the Moon during a lunar eclipse was suggested as a proof of the rotundity of the Earth by two old Greek astronomers, Manilius and Cleomedes, who lived about 2000 years ago, and is one more illustration of the great powers of observation and the general acuteness of the natural philosophers of antiquity.
Footnotes:
[112] The time occupied by the Moon in passing through the penumbra, before and after a lunar eclipse, will generally run to about an hour for each passage. It will occasionally happen that the Moon gets immersed in a penumbra but escapes the dark shadow. Such an event will not be announced in the almanacs under the head of “Eclipses.”
[113] See p. 197 (post).
[114] The shadow is spoken of as being in the form of a cone because it is necessarily such on account of the light-giving disc of the Sun being so enormously larger in diameter than the light-receiving sphere of the Moon. This idea can be pursued by any reader with the aid of a lamp enclosed in a glass globe and an opaque sphere such as a cricket ball.
[115] See p. 19 (ante).
[116] As to occultations see chap. xxi. (post).
[117] Month. Not., R.A.S., vol. viii. p. 132. March, 1848.
[118] A very striking chromolithograph of the lunar eclipses of Oct. 4, 1884, and Jan. 28, 1888, showing the contrast of—(1) an almost invisible grey Moon, and (2) a reddish-pink Moon, will be found in the German astronomical monthly, Sirius, vol. xxi. p. 241. Nov. 1888.
[119] Month. Not., R.A.S., vol. xlv. p. 35.