[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.
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.
7. The _Ecliptic_ is that great circle in whose plane the Earth performs its annual motion round the Sun; or, in which the Sun seems to move round the Earth, once in a year. This circle makes an angle with the equinoctial of 23 degrees 29 minutes, and intersects it in two opposite points, which are called the _Equinoctial Points_; and the two points in the ecliptic that are at the greatest distance from the equinoctial points, are called the _Solstitial Points_. The two meridians passing through those points, are, by way of eminence, called _Colures_; whereof that which passeth thro’ the equinoctial points, is called the _Equinoctial Colure_; and that which is at right angles to it, passing through the Solstitial Points, is called the _Solstitial Colure_.
[Sidenote: The Ecliptic divided into signs.]
The ecliptic is divided into 12 equal parts, called _Signs_, each sign being 30 degrees, beginning from one of the equinoctial points, and numbered from West to East; the names and characters of the twelve signs are as follows, _viz._