The description and use of the globes and the orrery / To which is prefix'd, by way of introduction, a brief account of the solar system

by Joseph Harris

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.

Arctic Circle.
Arctic Pole.
Antarctic Circle.
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.

II. Of the Ecliptic.

Ecliptic.
Equinoctial.
Solstitial Points.
Colures.
Equinoctial Colure.
Solstitial Colure.

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.

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.