Aberration of Light 227
Altitude of the Sun, &c. 135
Annular eclipse 190
Annual parallax of the Fixed Stars; its discovery attempted by
Dr. Bradley 227; and by Dr. Herschel 241
Antarctic Circle 132
Aphelion 20, note 59
Apogee 186
Apparent Diameter of the Sun and Planets 53, note
Apsides 20, note
Appulse of the Moon 186
Arctic Circle 132
Aristotle and Plato taught that the Earth is in the centre of the
system 8
Asteroids 66; some peculiarities relating to them 68; supposed to
be the fragments of a large planet burst asunder 69
Astronomer; proofs that we may rely on his knowledge 29
Astronomy is of two kinds; heliocentric and geocentric 62; of the
Earth 87
Atmosphere; its Refractive Power and density 136; diminishes the
darkness of the Earth's shadow, causing its darkest part to con-
verge to a point before it reaches the Moon; the cause of twi-
light 193
Attraction exists in every part of the Earth 31. See Gravity
Axis of a revolving body, what; axes of the Sun and Planets in-
clined to their orbits 42; the Earth's revolution around its axis
is one of the most equable motions in nature 215; of the Sphere's
daily revolution 231
Binary Sidereal systems 245
Centre of Attraction of the Solar system 35
Ceres; her diameter; atmosphere; distance from the Sun; velocity;
inclination of her orbit 67
Circle, its division into degrees, minutes, &c. 22, 134; the basis of
all astronomical observations, 135 note; of perpetual apparition;
of perpetual occultation 232
Circles; corresponding on the Globe and in the Sphere 234
Glock; its disagreement with the Sun 216; only times in which they
agree 222
Comets 17; their number, orbits, and the direction in which they re-
volve; the orbits of 98 have been calculated from observation 81;
Comet of 1680; its velocity, &c.; Comet of 1531, 1607 and 1682,
33; its return in 1759 verified the theory of gravitation; their
comæ, or streams of light, do not consist of much solid matter;
Moon eclipsed by one 85; have no effect on the planetary
motions; whimsical opinion of Whiston respecting their use 86
Common centre of Gravity of the Earth and Moon 180, 181 note; of
the Universe 250
Conjunction of a planet; inferior, superior 59
Constellations; time of their arrangement unknown 230; about 90
in the whole 233
Copernican system 8, 11, and seq.; supposed by Tycho Brahe not to
be consonant with some parts of the Scriptures 9; general view
of it 12
Copernicus, the restorer rather than the founder of the system called
the Copernican 8
Cusps of the Moon 152
Cycle of the Moon 173
Cycle of the Sun 174, note
Day; its length to each planet 42; Sidereal day 215; Solar day 216
Declination of a Star 232
Density, what; comparative density of the Sun and planets 34, note;
of the Sun 51, note
Digit; 1-12th part of the diameter of the Sun or Moon 186
Division of the Circle; see Circle
Earth, The; revolves round the Sun; time and velocity of its re-
volution; its diameter 15; its orbit nearly but not quite cir-
cular 19; its eccentricity 20; the only one of all the planetary
orbits considered to be in a horizontal position 21; inclination
of the others to it 22; appareatly the centre of the system;
optical view of Astronomy 88; objections to the Earth's revo-
lution answered 90; absurdity of the contrary doctrine 91;
opinion of the ancients respecting it 93; its form 94; polar
diameter less than the equatorial; its polar regions are portions
of larger circles than the equatorial 97; plane of its orbit 101;
its axis declines from the perpendicular 234 degrees; inclines to
the plane of its orbit, or to the Ecliptic 66 degrees 104; cause of
the periodical return of the Seasons 16; always points the same
way 106; its annual progress round the Sun 107; the north
pole always inclines towards the Crab; that of Venus the con-
trary way, note 108; its daily revolution on its axis 110, is one
of the most equable motions in nature 215; is nearer to the Sun
in summer than in winter; why it is coldest in winter 118; passes
through the winter half of its orbit quicker by 7 days, and why
120; different consequences of sailing round it, eastward and
westward 129, 130; is sometimes 190 millions of miles nearer to
some of the Fixed Stars, than at other times 143, 241; is a moon to
the Moon 148; attracted out of the regular line of its orbit by
the Moon when in conjunction and opposition 179; the form of
the Earth's orbit therefore partakes of the form of the Moon's 181;
its shadow is 3 times as long as from the Earth to the Moon;
its darkness diminished by our atmosphere; its penumbra 193;
eccentricity of its orbit is diminishing 197; is about 24 hours and
three quarters in turning on its axis towards the Moon and why
205; has no upper or under side; north, south, east, and west are
relative terms 216; is not always at its places of aphelion and
perihelion at the solstices, nor exactly at its mean distance from
the Sun at the equinoxes; does not accurately turn once round
towards the Sun every 24 hours 220; proceeds eastward about
1 degree every day 221; its whole diameter does not form the
base of a triangle sufficiently extended to enable us to calculate
the distance of a Fixed Star 240
Excentricity of the orbit of a planet, what 19; of each planet 20;
that of the Earth's orbit is diminishing 197
Eclipses 182; if the Moon moved on the same plane with the Sun
and Earth-on the plane of the Ecliptic; we should have an
eclipse of the Sun every new Moon, and of the Moon always
at the full 174; her orbit is inclined to the orbit of the Earth
5 degrees, 9 minutes; her nodes are perpetually shifting 172;
the places of her nodes; if at the node at the new, we have an
eclipse of the Sun; if at the full, she is herself eclipsed 175; ele-
ments of an eclipse 182; the shadow of a planet is proportionable
to the sizes of the Sun and the Planet; the shadow of a primary not
sufficiently long to reach the next primary planet to it; but only
to eclipse its own moons 184; number of eclipses in a year; and
during the Moon's cycle 185; length of a total eclipse of the
Moon 186; the Moon's shadow, during an eclipse of the Sun
does not always reach the Earth 189; annular and total eclipses
of the Sun; Moon's shadow never more than 180 miles broad
on the Earth; duration of a total eclipse of the Sun cannot be
longer to one place than 4 minutes and 6 seconds, and why 190;
penumbra 191, 193; eclipse of the Sun, Nov. 1816, 192; account
of the total eclipse of the Sun of 1715, 193; the existing tables
do not answer for very ancient eclipses 195; hence it is by some
concluded that the whole planenetary system will be drawn to
the Sun 196; refuted 197; eclipse at the crucifixion super-
natural 198
Ecliptic, a circle in the sphere of the Fixed Stars, passing along
the middle of the Zodiac; the apparent path of the Sun, and why
so called; and of the Earth as seen from the Sun 100; meaning
of the term 101; why delineated on a globe; oblique in regard
to the poles 104
Elongation of a planet 59
Epact 173 note
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