what point of the starry heavens comes to'the 
same meridian at the same time, ?. id with 
the same altitude. The sun must be' at that 
point of the starry heavens, thus discovered. 
Or we can observe that point in the heavens 
which comes to the meridian at midnight, 
with a declination as far from the equator on 
one side as the sun’s is on the other side ; and 
il is evident the sun must be in tiiat part of 
the heavens which is diametrically opposite 
to this point. By either of these methods 
w r e may obtain a series of points in the hea- 
vens, through which the sun passes, forming 
a circle called the ecliptic. This circle has 
ts name from the circumstance, that all the 
eclipses of the /sun and moon are performed 
either actually in, or very near, the circum- 
ference of that circle. 
The ecliptic, or annual path of the sun, 
differs in situation from the equator ; for the 
sun rises above the equator in summer, and 
does not rise so high in winter. The points 
of the ecliptic where the sun is situated when 
he is most distant from the equator, are call- 
ed solstitial points ; and the distance between 
the equator and the ecliptic at the solstitial 
points, is called the obliquity of the ecliptic ; 
this is found to be about twenty-three and a 
half degrees. A B (tig. 1.) represents the 
ecliptic, inclined twenty-three and a half de- 
grees to the equator E Q. 
The equinoctial colure is the great circle 
which passes at right angles to tiie equator, 
through those two points of it that are inter- 
cepted by the ecliptic, called the equinoctial 
points. The solstitial colure is the other 
great circle at right angles to the equator, 
cutting it in the solstitial points. It passes 
through the poles of the ecliptic. 
If smaller circlesof the sphere are described 
touching the solstitial points, and at right 
angles to the axis, as A C, B D, they are tro- 
pics ; of which that on the south side of the 
equator is called the tropic of Capricorn, and 
that on the north side of the equator the 
tropic of Cancer. The two polar circles 
F G, I K, are at the same distance from the 
two poles. as the tropics are from the equa- 
tor ; that is, twenty-three and a half degrees. 
It is necessary here to mention the differ- 
ence between what is called the sensible and 
rational horizon. If we suppose that part of 
the surface of the earth on which we stand 
to be a plane, and to be extended every way 
till it reaches the heavens, this plane forms the 
sensible horizon. 'The rational horizon is a 
circle, the plane of which is parallel to the 
former, but passing through the centre of the 
earth. Though the globe of the earth ap- 
pears so large to those who inhabit it, yet it 
is so small when compared with the immense 
sphere of the heavens, that the distance be- 
tween the sensible and rational horizons is no- 
thing in comparison with it. 
.The zodiac is a broad portion of the hea- 
vens, which stretches about eight degrees on 
each side of the ecliptic ; it is divided into 
twelve parts, called signs ; and each sign into 
thirty parts, called degrees. If we imagine a 
number of great circles of the sphere standing 
at right angles to the plane of the ecliptic, 
and consequently intersecting each other in 
its poles, these are called circles of celestial 
longitude, and they will divide the ecliptic 
into equal parts. Upon the ecliptic is reckon- 
ed the longitude of any fixed star, beginning 
to reckon at that point where the ecliptic 
ASTRONOMY. 
167 
and the equator intersect each other in the 
vernal equinox, called the first point of Aries ; 
and the arch of any of the circles of celestial 
longitude intercepted between a star and the 
ecliptic, is the latitude of that star. The 
equator is divided into degrees, but they are 
called degrees' of right ascension, and from 
it to the poles the degrees of declination are 
reckoned upon the meridian of the place. 
Having now described the principal lines 
and points on the celestial sphere, as gene- 
rated by the apparent motions of the hea- 
venly bodies, in which we have supposed 
what appears at first sight to be the case, viz. 
that the earth stands still while all the hea- 
venly bodies revolve round it. This will 
make no difference with regard to these 
circles in the heavens ; for it will be the same 
thing with respect to them, whether the 
earth is at lest, and the heavenly bodies 
move round it, or whether the latter remain 
still, and the earth, as we shall -afterwards 
see, moves round on its axis once every 
twenty-four hours. 
Of the Solar System If we examine the 
heavens in a clear night, we shall discover 
some stars which have brighter and steadier 
light than the rest ; and if we continue to 
observe these for several nights, we shall find 
that they do not appear in the same place 
among the rest of the stars every night, but 
that they have motions peculiar to them- 
selves. All the rest of the stars, rising 
and setting always exactly in the same 
places, are called fixed stars. Those 
wandering or moving stars, are called pla- 
nets. 
It is now fully proved, that these planets, 
with the earth which we inhabit, and also the 
moon, revolve round the sun, which Is fixed 
in the centre of the system. There are two 
kinds of planets, primary and secondary. The 
first move round the sun, and respect him 
only as the centre of their motions. The 
secondary planets, called also satellites or 
moons, are smaller planets, revolving round 
the primary ; while they, with the primary 
planets about which they move, are carried 
round the sun. The planets move round 
the sun at various distances, some being 
much nearer to him than our earth, and others 
being much farther off. 
Of these, our earth is accompanied by one 
moon, Jupiter has four moons, Saturn has 
seven, and the Herschel planet has six 
moons. IS! one of these moons, except our 
own, can be seen without a good telescope. 
The other five planets do not appear to have 
any satellites or moons. 
There are ten primary planets, which are 
situated with respect to their distances from 
the sun as follows : Mercury $ , Venus 5 , 
the Earth ©, Mars $ , Ceres, Pallas, Juno, 
Jupiterlf, Saturn 1? , and the Herschel or 
Geovgium Sid us $ . See Astronomy Plate, 
Solar System. 
All the planets move round the sun from 
east to west, and in the same direction do 
the moons revolve round their primaries ; 
excepting those of the Herschel planet, 
which seem to move in a contrary direction. 
The paths in which they move round the sun 
are called their orbits. These orbits are el- 
liptical ; but the eccentricity of the ellipses 
is so small, that they approach very nearly 
to circles. They perform their revolutions 
also in very different periods of time. The 
time of performing their revolutions is called 
their year. 
The Sun, 
Mercury, 
Venus, 
The Earth, 
The Moon, 
Mars, 
Ceres Ferdinandea, 
Pallas, 
Juno, 
Jupiter, 
Saturn, 
Herschel, 
| ® — ^3 rt I gooC 
" Ol 
Apparent mean 
diameters, as 
seen from the 
Earth. 
813,246 
3,224 
7,867 
2,180 
4,189 
160 
80 
89,170 
79,042 
35,112 
Mean dia- 
meters, in 
English 
miles. 
37.000. 000 
68.000. 000 
95,000,000 
95,000,000 
144.000. 000 
260.000. 000 
266,000,000 
300.000. 000 
490.000. 000 
900.000. 000 
1,800,000,000 
Mean distances 
from the Sun, 
in round num- 
bers of miles. 
25d. 14h. 8m. 
unknown. 
Od. 23h. 21m. 
Id. 
29d. 17b. 44m. 3s. 
0 24 39 22 
unknown, 
unknown. 
Od. 9h. 55m. 37s. 
0 10 16 2 
unknown. 
Diurnal rotations, 
1 or round their 
own axes. 
C O M 
-I -1 00 0 H Cl) CO to 
COCnOO-^O^OO Cl 10 00 
*-'l to tO CO ZC ^0 Cri CO 
I P- 1 
— — H B to 1 — 10 
OOW^OttOBI C5 c; 00 
tr ?! I pr 1 
cj, to *. ? Ob a. ~ 
O O O tO CT! 
3 OlH 2 
Time of revolving 
round the Sun. 
to. CO >-■ 
CO-4 
►fc. to Ci CO Oi to I 
Cl O CO 0 C --1 ^ O I CO 0 
to C -1 Cn ^ Oi CO 
cccioooicw 01 q 
Inclination of 
the orbits of 
the Ecliptic. 
82° 44 / 0" 
unknown, 
unknown. 
66° 32' 0 
88 17 0 
59 22 0 
unknown, 
unknown, 
unknown. 
90° O' 0" 
60 9 0 
unknown. 
Inclination of 
the axes to 
the orbits. 
> 
td 
r 1 
rtf 
O 
O 
> 
CO 
CO 
The planets are evidently opaque bodies, 
and they shine only by reflecting the light 
which they receive 'from the sun ; for Mer- 
cury and Venus, when viewed by a tele- 
scope, often appear to be only partly illumi- 
nated, and have the appearance of our 
moon when she is horned, having the illumin- 
ed part always turned towards us. From 
the appearance of the boundary of light 
and shadow upon their surfaces, we conclude 
that they are spherical ; which is confirmed 
by most of them having been found to turn 
periodically on their axes. 
Venus and Mercury being nearer to the 
sun than our earth, are called inferior planets ; 
and all the rest, which are without the 
earth’s orbit, are called superior planets. 
That the first go round the sun is certain], 
because they are seen sometimes passing 
between us and the sun, and sometimes they 
