ASTRONOMY. 
mean obliquity of the ecliptic to the beginning of the year 
r.769, was 23 0 28' 9"7''. 
To find the obliquity of the ecliptic, or the greateft de¬ 
clination of the Sun: about the time of the fummer fol- 
flice obfe: ve very carefully the Sun’s zenith diftance tor 
feveral days together ; then the difference between this dif¬ 
tance and the latitude of the place will be the obliquity 
fought, when the Sun and equator are both on one fide of 
the place of obfervation; but their turn will be the obli¬ 
quity when they are on different fides of it. Or, it may¬ 
be found by obferving the meridian altitude, or zenith dif¬ 
tance,.oft the Sun’s centre, on the days of the fummer and 
winter folliice;. then the difference of the two will be the 
diftance between the tropics, the half of which will be 
the obliquity fought. 
By the fame method too, the declination of the Sun from 
the equator for "any other day may be found; and thus a 
table of his declination for every day in the year might be 
conftructed. Thus alfo the declination of the ftars might 
be found.. 
Authors’ Names. 
Years before 
Chrift. 
Obliquity. 
Pytheas 
324 
O / // 
23 49 2 3 
Eratofthene 3 and Hipparchus 
230 & 140 
After Chrift. 
23 51 20 
Ptolemy ... 
140 
23 43 45 
Almaimon 
832 
23 35 
Albategnius 
880 
23 35 
Thebat ... 
911 
23 33 3° 
Abul Waft and Hamed 
999 
23 35 
Perfian Tables in Chryfococea 
1004 
23 35 
Albatrtmius 
1007 
23 35 
Arzachel 
1104 
23 33 3° 
Almaeon - 
1140 
23 33 3 ° 
Choja Naffir Oddin 
1290 
2.3 30 
Prophatius the Jew 
1300 
23 32 
Ebn Shattir 
i 3 6 3 
23 3i 
Purbuch and Regiomontanus 
1460. 
23 3 ° 
Ulugh Beigh - 
1463 
23 3 ° 17 
Walther 
1476 
23 3 ° 
Do. correiSIedbyrefraftion.&c 
— 
23 29 8 
Werner 
1510 
23 28 30 
Copernicus ... 
! 5 2 5 
23 28 24 
Egnatio Danti 
L 57 ° 
23 29 
Prince of HefTe 
157 ° 
23 3 i 
Rothman and Byrge 
157 ° 
23 30 20 
Tycho Brahe 
i 5 8 '4 
23 3 1 3 ° 
Ditto corrected 
— 
23 29 
Wright ... 
J 594 
23 3 ° 
Kepler 
1627 
23 3 ° 3 ° 
GafTendus ... 
1630 
23 3 1 
Ricciolus 
1646 
23 3 ° 20 
Ditto corrected 
l6 55 
23 29 
Hevelius 
i fi 53 
23 30 20 
Ditto correfled 
1661 
23 28 32 
Caflini ... 
1655 
23 29 15 
Montons, corrected, &c. 
1660 
23 29 3 
Richer, corrected 
1672 
23 28 32 
De la Hire 
16S6 
23 29 
Ditto corrected 
._ 
23 29 28 
Flamfteed 
1690 
23 29 
Bianchini 
i 7°3 
23 28 2; 
Roemer ... 
1706 
23 28 41 
Louville 
1715 
23 28 24 
Godin - 
173 ° 
23 28 20 
Bradley 
175 ° 
23 28 18 
Mayer - 
I 75 6 
23 28 16 
Mafkelyne 
1769 
23 28 10 
Hornfby ... 
1772 
23 28 8 
The obfervations of aftronomers of all ages, on the 
obliquity of the ecliptic, have been collected together; 
and, although lome of them may not be quite accurate, yet 
$hey fufficiently fhew the gradual and continual decreafe 
x 
of the obliquity from the times of the earlieft obfervations 
down to the prefent time. The chief of thofe obferva¬ 
tions may be feen in the foregoing Table ; where the firft 
column contains the name of the obferver or author, the 
fecond the year before or after Chrift, and the third the 
obliquity of the ecliptic for that time. 
According to an ancient tradition of the Egyptians, men¬ 
tioned by Herodotus, the ecliptic had formerly been per¬ 
pendicular to the equator: they were led into this notjon 
by obferving, for a long feries of years, that the obliquity 
was continually diminifliing; or, which amounts to the 
fame thing, that the ecliptic was continually approaching 
to the equator. From thence they took occafion to fill- 
pe£t that thofe two circles, in the beginning, had been as 
far off each other as poftible, that is, perpendicular to 
each other. Diodorus Siculus relates, that the Chaldeans 
reckoned 403,000 years from their firft obfervations to the 
time of Alexander’s entering Babylon. This enormous 
account may have fome foundation, on the fuppofition that 
the Chaldeans built on the diminution of the obliquity of 
the ecliptic at the rate of a minute in 100 years. M. de 
Louville, taking the obliquity fuch as it mull have been 
at the time of Alexander’s entrance into Babylon, and go¬ 
ing back to the time when the ecliptic, at that rate, mud 
have been perpendicular to the equator, actually finds 
402,942 Egyptian or Chaldean years; which is only fifty- 
eight years ftiort of that epocha. Indeed there is no way 
of accounting for the fabulous antiquity of the Egyptians, 
Chaldeans, &c. fo probable, .as from the fuppofition of 
long periods of very flow celeftial motions, a fmall part oft 
which they had obferved, and from which they calculated, 
the beginning of the period, making the world and their 
own nation to commence together. Or perhaps they fome- 
times counted months or days for years. Should the di¬ 
minution always continue at the rate it has lately done, 
viz. at 50" or 56" a century, it would take 96,960 years, 
from the year 1788, to bring tire ecliptic exaitly to coin¬ 
cide with the equator. For particulars concerning the di- 
vifion of time, the alteration of the ftyle, &c. &c. fee the 
article Y ear. 
Of the MOON. 
The Moon is a fateliite, or fecondary planet of the 
Earth, confidered as a primary one, about which the re¬ 
volves in an elliptic orbit, or rather the Earth and Moon 
revolve about a common centre of gravity, which is as 
much nearer to the Earth’s centre than to the Moon’s, as- 
the mafs 01 the former exceeds that of the latter. 
Next to the Sun, the is the moil fplendid and fhining. 
globe in the heavens ; and by diflTpating, in fome meafure, 
the darknefs and the horrors of the night, fubdividing the 
year into months, and regulating the flux and reflux of 
the fea, the not only becomes a pleafing, but a welcome, 
object; affording much for fpeculation to the contempla¬ 
tive mind, and of real life to the navigator, the traveller,,, 
and the hufbandman. The Hebrews, the Greeks, the 
Romans, and, in general, all the ancients, ufcd to aflem-- 
ble at the time of the new Moon, to difeharge the duties 
of piety and gratitude for its manifold ufes. 
That the Moon appears fo much larger than the other' 
planets, is owing to her vicinity to us ; for to a fpetlator 
in the Sun fhe would be fcarcely viiible, without the aflif- 
tance of a telefcope. Her diftance is but 1 fmall from us, 
when compared with that of the other heavenly bodies; 
for among thefe, the leaft abfolute diftance, when put 
down in numbers, will appear great, and the fmalleftrm ig- 
nitude immenfe. If the Moon were a body poflefling na¬ 
tive light, we fttould not perceive any diverfity of appear¬ 
ance ; but as fhe fhines entirely by light received from the 
Sun, and reflected by her furface, it follows, that, ac¬ 
cording to the fituation of the beholder with refpeot to the 
illuminated part, he will fee more or lefs of her reflefted 
beams, for only one half of a globe can be enlightened at 
once. Hence, while fhe is making her revolution round 
the heavens, fhe undergoes great changes in her appear¬ 
ance. In every revolution of the Moon about the Earth, , 
