Ecliptic
Definition
The Ecliptic is the apparent path of the Sun on the celestial sphere, as observed from Earth. It is the circular path that the Sun appears to follow over the course of a year, as it moves through the constellations of the Zodiac.
Overview
The term "ecliptic" comes from the Greek word "ekleipsis", meaning "an abandonment or omission". In astronomy, this term was used to describe the path that the Sun seems to abandon as it moves across the sky. The ecliptic is not only the path of the Sun, but also the plane of Earth's orbit around the Sun. The other planets in the Solar System also orbit the Sun in roughly the same plane.
Understanding the Ecliptic
The ecliptic is an essential concept in astronomy as it is the baseline for the celestial coordinate system. The celestial equator, which is a projection of Earth's equator onto the celestial sphere, intersects the ecliptic at two points: the vernal equinox and the autumnal equinox. These points mark the beginning of spring and autumn, respectively.
Ecliptic Plane
The ecliptic plane is the plane of Earth's orbit around the Sun. This plane is used as the primary reference when describing the position and orbits of bodies in the Solar System. The inclination of Earth's equator to the ecliptic plane (approximately 23.4 degrees) is responsible for the changing of the seasons.
Ecliptic and the Zodiac
The ecliptic passes through the 13 constellations of the Zodiac. These constellations have been significant in both astronomy and astrology. The Sun, Moon, and planets all move along the ecliptic, and their positions can be described relative to the Zodiac constellations.
Ecliptic and the Moon
The Moon's orbit is inclined to the ecliptic by about 5 degrees. Therefore, the Moon can be found anywhere within about 5 degrees of the ecliptic. This is why solar and lunar eclipses can only occur when the Moon crosses the ecliptic at the new or full phase.
Ecliptic and the Planets
The planets in the Solar System also orbit the Sun in roughly the same plane as the ecliptic. Therefore, like the Moon, the planets can usually be found within a few degrees of the ecliptic.