261. The Moon generally appears as large as the Sun; for the Angle _vkA_, under which the Moon is seen from the Earth, is the same with the Angle _LkM_, under which the Sun is seen from it. And therefore the Moon may hide the Sun’s whole Disc from us, as she sometimes does in solar Eclipses. The reason why she does not eclipse the Sun at every Change shall be explained afterwards. If the Moon were farther from the Earth as at _a_, she could never hide the whole of the Sun from us; for then she would appear under the Angle _NkO_, eclipsing only that part of the Sun which lies between _N_ and _O_: were she still further from the Earth, as at _X_, she would appear under the small Angle _TkW_, like a spot on the Sun, hiding only the part _TW_ from our sight. [Sidenote: A proof of the Moon’s turning round her Axis.] 262. The Moon turns round her Axis in the time that she goes round her orbit; which is evident from hence, that a spectator at rest, without the periphery of the Moon’s orbit, would see all her sides turned regularly towards him in that time. She turns round her Axis from any Star to the same Star again in 27 days 8 hours; from the Sun to the Sun again in 29-1/2 days: the former is the length of her sidereal day, and the latter the length of her solar day. A body moving round the Sun would have a solar day in every revolution, without turning on it’s Axis; the same as if it had kept all the while at rest, and the Sun moved round it: but without turning round it’s Axis it could never have one sidereal day, because it would always keep the same side towards any given Star. [Sidenote: Her periodical and synodical Revolution.] 263. If the Earth had no annual motion, the Moon would go round it so as to compleat a Lunation, a sidereal, and a solar day, all in the same time. But, because the Earth goes forward in it’s orbit while the Moon goes round the Earth in her orbit, the Moon must go as much more than round her orbit from Change to Change in compleating a solar day as the Earth has gone forward in it’s orbit during that time, _i. e._ almost a twelfth part of a Circle. [Sidenote: Familiarly represented. A Table shewing the times that the hour and minute hands of a watch are in conjunction. A machine for shewing the motions of the Sun and Moon. PL. VII.]