•3$o 
ASTRONOMY. 
motion of the apogee he fubtradPed from the mean motion 
of the Moon, the remainder will be the Moon’s mean mo¬ 
tion from the apogee ; and hence, by the Rule of Three, 
the quantity of the anomaliflic month is determined. 
Thus, according to Kepler’s obfervations, 
The mean fynodical month is 2gd. i2h. 44' 
The periodical month 27 7 43 
• 3 ". 
8 
2'" 
The place of the apogee for the"! r 
year 1700, Jan. 1, old (Pyle, was J 11 " 
8°. 
57 '- 
1" 
The place of the afeending node 4 
27 
39 
17 
Mean diurnal motion of the Moon 
1 3 
10 
35 
Diurnal motion of the apogee . 
6 
41 
Diurnal motion of the nodes 
• 
3 
1 r 
Therefore diurnal motion from the latter . 
13 
13 
46 
And the diurnal motion from the apogee . 
13 
3 
54 . 
Tartly, the eccentricity is 4362, of fuch parts as the femi- 
Qiater of the eccentric is 100,000. 
To find, nearly the Moon's Age or Change. —To the epadt 
add the number and day of the month ; their I'um, abat¬ 
ing thirty if it be above, is the Moon’s age; and her age 
taken from thirty (hews the day of the change. The 
numbers of the months, or monthly epacts, are the Moon’s 
age at the beginning of each month, when the folar and 
lunar years begin together; and are thus : 
02 123456 88 10 10 
Jan. Feb. Mar. Ap. Ma. jun. Jul. Aug. Sep. 061. Nov. Dec. 
Ex. To find the Moon’s age the 14th of Odt. 1 783. 
Here, the epadp is 26 
Number of the month 8 
Day of the month 14 
The fum is 48 
Subtract or abate 30 
Leaves Moon’s age 18 
Taken from 30 
Days till the change 12 
Anfwering to Oft. 26 
To find nearly the Moon's Southing, or coming to the Meri¬ 
dian. —Take a 0 r of her age, for her fouthing nearly ; 
after noon, if it be lefs than twelve hours; but, if greater, 
the excefs is the time after laft midnight. 
Ex. Odlober 14, 1783 : 
The Moon’s age is 18 days 
fin of which is 14-4 or 14b. 24'. 
Subtract 12 00 
Rem. Moon’s fouthing 2 24 in the morning. 
Mr. Fergufon, in his Seledt Exercifes, p. 135, &c. has 
given very eafy tables and rules for finding the new and 
full Moons near enough the truth for any common alma¬ 
nac. But the Nautical Almanac, which is now always pub- 
lifhed for feveral years before hand, in a great meafure fu- 
perfedes the necellity of thefe and other fuch calculations. 
Of the Spots and Mountains, See . in the Moon. 
The face of the Moon is greatly diverfified with inequa¬ 
lities, and parts of different colours, fpme brighter and 
fome darker than the other parts of her difk. When 
viewed through a telefcope, her face is evidently diverfi- 
fied with hills and valleys : and the fame is alfo fhewn by 
the edge or border of the Moon appearing jagged, when 
fo viewed, efpecially about the confines of the illuminated 
part when the Moon is either horned or gibbous. The 
artronomers Florenti, Langreni, Hevelius, Grimaldi, Ric¬ 
cioli, CafTini, and De la Hire, Sec. have drawn the face 
of the-Moon as viewed through telefcopesy noting all 
the more Ihining parts, and, for the better diftindfion, 
•marking them with fome proper name ; fome of thefe au¬ 
thors calling them after the names of philofophers, aftro- 
nomers, and other eminent men ; while others denominate 
them from the known names of the different countries, 
irtands, and feas, on the Earth. The names adopted by 
Riccioli however, are moitly followed, as the names of 
Hipparchus, Tycho, Copernicus, See . In the Aftrono- 
mical-Plate IV. fig. 1. Is given an accurate reprefentatiot 
of the full Moon in her mean libration, with the numbers 
referring to the principal fpots according to Riccioli, Caf- 
fini, Mayer, &c. which denote the names in the followin®- 
lift. 
1 Grimaldi 2 6 Hermes 
2 Galileo 27 Portidonius 
3 Ariftarchus 28 Dionyfius 
4 Kepler 29 Pliny 
5 GalPendi f Catharina Cyrillus, 
6 Shikard - \ Theophilus 
7 Harpalus 31 P'racaftor 
8 Heraclides- o f Promontorium, acu- 
9 Lanfberg ** \ turn, Cenforinus 
jo Reinhold 33 Meffala 
11 Copernicus 34 Prornontorium Somnii 
12 Helicon 35 Proclus 
13 Capuanus 36 Cleomedes 
14 Bulliald 37 Snell and Furner 
15 Eratorthenes 38 Petavius 
16 Timocharis 39 Langremls 
• 17 Plato 40 Taruntius 
iS Archimedes A Mare Humorum 
19 Infitla Sinus Medii B Mare Nubium 
20 Pitatus C Mare Imbrium 
21 Tycho D~ Mare Nectaris 
22 Eudoxus E Mare Tranquillitatis 
23 Ariftotle F Mare Serenitatis 
24 Manilius G Mare Foecunditatis 
25 Menelaus H Mare Crifium 
That the fpots in the Moon, which are taken for moun¬ 
tains and Valleys, are really fuch, is evident from their 
fliadows. For in all fituations of the Moon, the elevated 
parts are conftantly found to cart a triangular fhadow in a 
aireftion from the Sun ; and, on the contrary, the cavities 
are always dark on the fide next the Sun, and illuminated 
on the oppofite one; which is exadlly conformable to what 
we obferve of hills and valleys on the Earth. And, as the 
tops of thefe mountains are confiderably elevated above 
the other parts of the furface, they are often illuminated 
when they are at a confiderable diftance from the confines 
of the enlightened hemifphere, and by this means afford 
us a method of determining their heights. 
Thus Riccioli obferved the top of the hill called St. 
Catherine, on the fourth day after the new Moon, to be 
illuminated when it was diftant from the confines of the 
enlightened hemifphere about i-i6th part of the Moon’s 
diameter; and lie thence concluded its height murt be near 
nine miles. It is probable, however, that this determina¬ 
tion is too much. Indeed, Galileo makes it only five miles 
and a half, and Hevelius only three and a quarter miles, 
and probably it lhould be (Pill lefs than either of thefe; 
for they are greatly reduced by the obfervations of Dr. 
Herfchel, whole method of meafuring them may be feen 
in the Philof. Tranf. an. 1780, p. 507. This gentleman 
meafured the height of many of the lunar prominences, 
and draws the following conclufions 1 “ From thefe ob-’ 
fervations I believe it is evident, that the height of the 
lunar mountains in general is greatly over-rated; and that, 
when we have excepted a few, the generality do not ex¬ 
ceed half a mile in their perpendicular elevation.” 
M. Schroeter, however, of .he Royal Society of Got¬ 
tingen, in the year 1792, feems to have taken great pains 
to invertigate the truth of this matter. According to him, 
the furface of the Moon appears to be much more unequal 
than that of our Earth ; and thefe inequalities have great 
variety both in form and magnitude. There are large ir¬ 
regular plains, on which are obferved 'long and narrow 
rtrata of hills running in a ferpentine diredlion : fome of 
the mountains form extenfive chains; others, which are 
in general the higheft, (land alone, and are of a conical 
(hape: fome have craters; others form a circular ring in- 
clofing a plain; and, in the centre of many of thefe plains, 
as well as in the middle of fome of the craters, other moun¬ 
tains are found, which have likevvife their craters. Thefe 
mountains 
