[Sidenote: The _Equator_, or _Equinoctial_.]
1. The _Equator_, or the _Equinoctial_, is that great circle in the
Heavens, in whose plane the Earth performs her diurnal motion round her
axis; or it is that great circle, parallel to which the whole Heavens
seem to turn round the Earth from East to West in 24 Hours.
_Note_, The Equator and the Equinoctial are generally synonymous terms;
but sometimes the Equator particularly signifies that great circle upon
the surface of the Earth, which coincides with the Equinoctial in the
Heavens. This circle is also by Mariners commonly called the _Line_.
[Sidenote: _Northern_ and _Southern Hemispheres_.]
[Sidenote: _The Axis of the World._]
[Sidenote: _Poles of the World_, or _of the Equator_.]
The equinoctial divides the globe of the Earth, and also the whole
Heavens into two equal parts, North and South, which are called the
_Northern_ and _Southern Hemispheres_. The axis of this circle, is
called the _Axis of the World_, or the _Earth’s Axis_, because the
Earth revolves about it (from West to East) in 24 hours. The extreme of
this axis are called the _Poles of the World_, whereof that which lies
in the Northern Hemisphere, is called the _North Pole_, and the other
is called the _South Pole_. The equinoctial circle is always delineated
upon the surface of each globe, with its name at length expressed; the
axis of this circle, or the Earth’s axis, is only an imaginary line in
the Heavens, but on the globes it is expressed by the wires about which
they really turn. The Poles of the world, are the two points upon the
surface of the globe through which these wires pass; the North Pole is
that which hath the little brass circle, with a moveable index placed
round it; and the other opposite to it is the South Pole. The Northern
Hemisphere is that wherein the North Pole is placed, and the opposite
one is the Southern Hemisphere.
The astronomers divide all circles into 360 equal parts, called
_Degrees_, each degree into 60 equal parts, called _Minutes_, each
minute into 60 _Seconds_, &c. But besides this division into degrees,
the equinoctial is also divided into 24 equal parts, or _Hours_, each
hour into 60 _Minutes_, each minute into 60 _Seconds, &c._ so that one
hour is equal to 15 degrees, each minute of time is equal to 15 minutes
of a degree, _&c._
[Sidenote: _Hour Circles_ or _Circles of Ascension_, also called
_Meridians_.]
2. All circles conceived to pass through the Poles of the world,
intersecting the equinoctial at right angles, are, with respect to
any point in the Heavens, called _Hour Circles_; and the _Circles
of Ascension_, because the ascension of the Heavenly bodies, from a
certain point, are by them determined.
These circles are also, with regard to places upon Earth, called
_Meridians_.
[Sidenote: The _Brass Meridian_.]
The _Meridians_ are commonly drawn upon the Terrestrial Globe thro’
every 15 degrees of the equinoctial, thereby making an Hour difference
betwixt the places through which they pass. On the Celestial Globe
there are commonly drawn but two of these _Meridians_, crossing the
equinoctial in four points equidistant from one another, thereby
dividing it into four quadrants; but the intermediate ones are here
supplied, and also upon the Terrestrial Globe, by the brass circle on
which they are hung, which, is therefore called the _Brass Meridian_,
and sometimes only the _Meridian_, it serving for this purpose to all
the points upon either Globe.
[Sidenote: The _Hour Circle_.]
There is also a little brass circle fixed upon this meridian, divided
into 24 Hours, having an index moveable round the axis of the globe, to
be turned to any particular Hour. The use of this circle is to shew the
difference of time betwixt any two meridians, and is therefore called
the _Hour Circle_.
[Sidenote: _Parallels of Declination._]
3. All circles parallel to the equinoctial are, with respect to any
point in the Heavens, called _Parallels of Declination_. So that,
[Sidenote: _Declination North_ and _South_.]
4. The _Declination of any Point_ in the Heavens (as of the _Sun_, a
_fixed Star_, or the like) is an arch of the meridian passing through
that point, and intercepted betwixt it and the equator; and if the
said point be to the (Northward/Southward) of the equator, it is
called (_North_/_South_) _Declination_.
[Sidenote: _Tropics_ and _Polar Circles_.]
Of the parallels of declination, four are eminently distinguished by
particular names, _viz._ The two _Tropics_, and the two _Polar Circles_.
[Sidenote: _Tropic of Cancer; of Capricorn._]
The tropics are on different sides of the equator each 23 degrees and
29 minutes distant from it; that which lies in the Northern Hemisphere,
is called the _Tropic of Cancer_, and the Southern one, the _Tropic of
Capricorn_.
These circles are the limits of the Sun’s greatest declination, and are
called tropics, because whenever the Sun arrives to them, he seems to
return back again towards the equator.
[Sidenote: _Arctic Circle._]
[Sidenote: _Arctic Pole._]
[Sidenote: _Antarctic Circle._]
[Sidenote: _Antarctic Pole._]
6. The _Polar Circles_ are each of them at the same distance from the
Poles of the world, that the tropics are from the equator, _viz._
23° 29′. That which lies near the North Pole, is called the _Arctic
Circle_, from _Arctos_, a constellation situated in the Heavens near
that Place; whence also this Pole is sometimes called the _Arctic
Pole_. The other Polar circle, which is situated near the South Pole;
is called the _Antarctic Circle_, because its position is contrary to
the other; and the South Pole is sometimes called the _Antarctic Pole_.
The tropics and the Polar circles have each their names expressed upon
the Globes.