3*6 ASTRONOMY. 
tic and equator being great circles mull bifect each other, 
and their angle of inclination is called the obliquity of the 
ecliptic ; alio the points where they interfefl are called the 
equinoBial points. The times w hen the fun comes to thefe 
points are called the equinoxes. 
The ecliptic is divided into twelve equal parts, called 
figns ; 7" Aries, £$ Taurus, n Gemini, 25 Cancer, 
Leo, nJt Virgo, Libra, Ilf Scorpio, Sagittarius, 
V? Capricornus, Aquaries, X Pifces. The order of 
thefe is according to the motion of the fun. The firft point 
of Aries coincides with one of the equinoctial points, and 
the firft point of Libra with the cither. The firft fix figns 
are called northern , lying on the north fide of the equator ; 
and the laft lix are called fouthern, lying on the fouth fide. 
The figns Vf, X, X> YT , H> are called afeending , the 
fun approaching our (or the north) pole whilft it palfes 
through them; and s, Q, rtf, ii, Uf, $ , are called 
defending, the fun receding from our pole as it moves 
through them. 
The motion of the heavenly bodies which is according 
to the order of the figns is called direB, or in confcqutntia ; 
and the motion in the contrary direction is called retrograde , 
or in antecedentia. The real motion of all the planets is ac¬ 
cording to the order of the figns, but their apparent motion 
is fometimes in an oppofite direction, hence called retro¬ 
grade. The zodiac is a fpace extending 8° on each fide of 
the ecliptic, within which the motion of all the planets is 
contained. 
. The right afcenfion of a body is an arc of the equator in¬ 
tercepted between the firft point of Aries and a declination 
circle palling through the body, meafured according to the 
order of the figns. The oblique afcenfion is an arc of the 
equator intercepted between the firft point of Aries and 
that point of the equator which rifes with any body, mea¬ 
fured according to the order of the ligns. The afcenfional 
difference is the difference between the right and oblique 
afcenfion. 
The declination, of a body is its angular diftance from the 
equator, meafured upon a fecondary to it drawn through 
the body. 
The longitude of a (tar is an arc of the eclipic intercepted 
between the firft point of Aries and a fecondary to the 
ecliptic paffing through the body, meafured according to the 
order of the ligns. If the body be in our fyftem, and feen 
from the fun, it is called the heliocentric longitude ; but if 
feen from the earth it is called the geocentric longitude : the 
body in each cafe being referred perpendicularly to the 
ecliptic in a plane palling through the eye. 
The latitude of a ftar is its angular diftance from the eclip¬ 
tic, meafured upon a fecondary to it drawn through the body. 
If the body be in our fyftem, its angular diftance from the 
ecliptic feen from the earth is called the geocentric latitude; 
but if feen from the fun it is called the heliocentric latitude. 
The tropics are two parallels of declination touching the 
ecliptic. One, touching it at the beginning of Cancer, is 
called the tropic of Cancer ; and the other, touching it at the 
beginning of Capricorn, is called the tropic of Capricorn. 
The two points where the tropics touch the ecliptic are 
called the folficial points. 
Colures are two fecondaries to the celeftial equator, one 
palling through the equinoctial points, called the equinoBial 
colure ; and the other paffing through the follticial points, 
called the folficial colure. The times when the fun comes 
to the folfticial points are called the folfices. 
The arBic and antarBic circles are two parallels of de¬ 
clination, the former about the north and the latter about 
the fouth pole, the diftance of which from the two poles 
is equal to the diftance of the tropics from the equator. 
Thefe are alfo called polar circles. The two tropics and 
two polar circles, when referred to the earth, divide it 
into five parts, called zones ; the two parts within the polar 
circles are called the frigid zones ; the two parts between 
the polar circles and tropics are called the temperate zones; 
and the part between the tropics is called the torrid zone. 
A body is in conjunction with the fun, when it has the 
* 
fame longitude; in oppoftion, when the difference of their 
longitudes is i8o°; and in quadratures, when the difference 
of their longitudes is qo°. The conjunction is marked 
thus d, the oppofition thus §, and the quadratures thus 
Syzygy means either conjunction or oppofition. 
The elongation of a body is its angular diftance from the 
fun when feen from the earth. 
The diurnal parallax is the difference between the appa¬ 
rent places of the bodies in our fyftem when referred to 
the fixed liars, if feen from the center and furface of the 
earth. The annual parallax is the difference between the 
apparent places of a body in the heavens, when feen from 
the oppofite points of the earth’s orbit. 
The argument is a term ufed to denote any quantity by 
which another required quantity may be found. For ex¬ 
ample, the argument of that part of the equation of time 
which arifes from the unequal angular motion of the earth 
in its orbit about the fun is the fun’s anomaly, becaufe that 
part of the equation depends entirely upon the anomaly ; 
and, the latter being given, the former is found from it. 
The argument of a liar’s latitude is its diftance from its 
node, becaufe upon this the latitude depends. 
The nodes are the points where the orbits of the primary 
planets cut the ecliptic, and where the orbits of the fe¬ 
condaries cut the orbits of their primaries. That node is 
called afeending where the planet palfes from the fouth to 
the north fide of the ecliptic ; and the other is called the 
defending node. The afeending node is marked thus ££, 
and the defeending node thus fj. The line which joins 
the nodes is called the line of the nodes. 
If a perpendicular be drawn from a planet to the eclip¬ 
tic, the angle at the fun between two lines, one drawn 
from it to that point where the perpendicular falls, and ano¬ 
ther to the earth, is called the angle of commutation. 
The angle of pofition is the angle at an heavenly body 
formed by two great circles, one palling through the pole 
of the equator and the other through the pole of the ecliptic. 
Apparent noon is the time when the fun comes to the 
meridian. True or mean noon is twelve o’clock, by a clock 
adjufted to go twenty-four hours in a mean folar day. The 
equation of time is the interval between trz^and apparent noon. 
A ftar is faid to rife or fet cofmically, when it rifes or fets 
at fun-rifing ; and when it riles or fets at fun fetting, it is 
laid to rife or fet achronically. A ftar rifes heliacally, when, 
after having been fo near to the fun as not to be vilible, it 
emerges out of the fun’s rays and juft appears in the morn¬ 
ing ; and it fets heliacally, when the fun approaches fo near 
to it, that it is about to immerge into the fun’s rays and 
become invifible in the evening. 
Curtate difance of a planet from the fun or earth is the 
diftance of the fun or earth from that point of the ecliptic 
w here a perpendicular to it pafles through the planet. 
Aphelion is that point in the orbit of a planet which is 
fartheft from the fun. Perihelion is that point in the orbit 
of a planet which is neareft to the fun. Apogee is that 
point of the earth’s orbit which is fartheft from the fun, 
or that point of the moon’s orbit which is fartheft from 
th$ earth. Perigee is that point of the earth’s orbit which 
is neareft to the fun, or that point of the moon’s orbit 
which is neareft to the earth. The terms aphelion and 
perihelion are alfo applied to the earth’s orbit. 
Apfis of an orbit is either its aphelion or perihelion, apo¬ 
gee or perigee; and the line which joins the apfides is 
called the line of the apfdes. 
Anomaly (true) of a planet is its angular diftance at any 
time from its aphelion, or apogee— (mean) is its angular 
diftance from the fame point at the fame time if it had 
moved uniformly with its mean angular velocity. Equation 
of the center is the difference between the true and mean ano¬ 
maly ; this is fometimes called the profhapherefis. 
Nonagefmal degree of the ecliptic is that point which is 
higheft above the horizon. 
The mean place of a body is the place where a body, 
not moving with an uniformly angular velocity about the 
central body, would have been, if the angular velocity 
had 
