J 20

Astronomy,

The First in I Day, 18 Hours, 27 ^

nutes, at the Distance of e-A Semidia^

tel-

pi, Liy.Fig. 6.

tj[e

ig. But fince this Motion about the Axis is ec l uS c , J iand uniform, and that about the Earth (or cov* 1 * 11 .^Centre of Gravity) is unequal and irregular, as b eIperformed in an Ellipsis, it must follow, that the ^Part of the Moon’s Surface precisely can never be ^constantly to the Earth ; and this is confirmed by, sTelescope, through which we often observe a little f

or Segment on the Eastern and Western Limb apP Jand disappear by turns, as if her Body librated tofro ; which therefore occasioned this Phænomeno 11be called the Moons Lihration. fi>

20. The Orbit of the Moon is elliptical, mo rC ^

than any of the Planets, and is perpetually changes jvariable, both in respect of its Figure and Situation >which we shall treat more largely in another fl (

The Inclination of the Moon’s Orbit to the P^ pe g>the Ecliptic is also variable, from 5 Degrees to 5 - 0 jiThe Line of Nodes likewise has a variable

from East to West, contrary to the Order of the S< Gand compleats an entire Revolution in a Space of >.u S)a little less than 19 Years. Also the Line of theor of the Jpogee and Perigee , has a direct Motion * {

Weft to East, and finishes a Revolution in the Sp 3C jjyabout 9 Years. All which will be more copjst^jtreated of when we come to explain the Physicalthereof.

21. The Phases of the Moon in every Part of .

Orbit are easily accounted for from her different S 1 ^tion with respect to the Earth and Sun : For thong §an Eye placed in the Sun she will always exhib'^ ecom pleat illuminated Hemisphere, yet in respect t0 ff(C cSEarth, where that Hemisphere is viewed in all st

of Obliquity, it will appear in every Degree fr 01 ? ^5greatest to the least ; so that at E no Part at all of ^ Q (enlightened Surface can be seen. At F a little P 3 ^ jtit is turned towards the Earth, and from its Fig 111 j;