Below are a list of words and their definitions to help you better understand what is being talked about throughout this website!
Celestial Sphere: An imaginary sphere of which the observer is the center and on which all celestial objects are considered to lie.
Celestial Equator: The projection into space of the earth's equator; an imaginary circle equidistant from the celestial poles.
Zenith: The point in the sky or celestial sphere directly above an observer
Ecliptic: a great circle on the celestial sphere representing the sun's apparent path during the year, so called because lunar and solar eclipses can occur only when the moon crosses it.
Eccentric Motion: parameter that determines the amount by which its orbit around another body deviates from a perfect circle.
Epicycle: geometric model used to explain the variations in speed and direction of the apparent motion of the Moon, Sun, and planets.
Precession: Change in the orientation of the rotational axis of a rotating body.
Equinox: This occurs twice a year, it is the time at which the sun crosses the celestial equatr, when day and night are of equal length.
Obliquity of the Ecliptic: Angle between the plane of the earth's orbit and that of the celestial equator. Acording to Ptolemy's estimations is was approximatly 27 degrees.
Chord of a Circle: Straight line segment whose endpoints both lie on the circle, ie a line segment joining two points n ay curve. A secant line is the infinite line extention of a chord.
Zodiac: a belt of the heavens within about 8° either side of the ecliptic, including all apparent positions of the sun, moon, and most familiar planets. It is divided into twelve equal divisions or signs (Aries, Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius, Pisces).