Ecliptic

Ecliptic is the apparent path of the Sun on the celestial sphere, and is the basis for the ecliptic coordinate system. It also refers to the plane of this path, which is coplanar with both the orbit of the Earth around the Sun and the apparent orbit of the Sun around the Earth.

Description

The ecliptic is actually the apparent path of the Sun throughout the course of a year. Because Earth takes one year to orbit the Sun, the apparent position of the Sun takes one year to make a complete circuit of the ecliptic. With slightly more than 365 days in one year, the Sun moves a little less than 1° eastward every day.

Ecliptic Plane

The plane of Earth's orbit around the Sun is the most important reference plane when discussing the motion of bodies in our solar system. This plane, known as the ecliptic plane, is the basis of the ecliptic coordinate system.

Ecliptic Coordinate System

The ecliptic coordinate system is a celestial coordinate system that uses the ecliptic for its fundamental plane. The system's origin can be the center of either the Sun or Earth, its primary direction is towards the vernal equinox, and it has a right-hand convention.

Relation to the Celestial Equator

The ecliptic intersects the celestial equator, the projection of Earth's equator onto the celestial sphere, at two points: the vernal and autumnal equinoxes. The angle between the ecliptic and the celestial equator is approximately 23.44 degrees, and is known as the obliquity of the ecliptic.

See Also

• Celestial sphere
• Celestial equator
• Equinox
• Solar System

References

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