Ecliptic coordinate system

The ecliptic coordinate system is one of the coordinate systems that are used in the spherical astronomy. In contrast to the equatorial coordinate system used as the reference plane of the equator of the earth, the reference plane is the plane described by the ecliptic ( the plane of the web is approximately the ground in its orbit around the sun).

Definition

The position of an object is specified by two coordinates:

• The ecliptic longitude indicates the angle opposite. is measured in the ecliptic plane in the direction of Erdumlaufs positive at 0 °. The following applies:

• The ecliptic latitude is the angle opposite to - the height above the ecliptic - and is 0 ° and 90 °. The following applies:

Since the ecliptic coordinate system refers neither to the current true vernal equinox even to the current point in mid Spring, a time reference must be specified in addition, is called the epoch. The mean vernal equinox exactly at this time is the equinox of the coordinates. At this point, the coordinates given refer. The date must be specified, because the mean vernal equinox moves through the precession against the starry sky, and the true vernal equinox varies by further disruptions to the mean vernal point.

The coordinate equinox can be chosen freely in principle ( which states the definition 2 ). One chooses to either a Standardäquinoktium (about J2000.0 ) for catalogs or the equinox of the date of measurement in direct observation of the heavens.

Also, the system refers to the equinox, not the current constellation of Earth-Sun: Therefore, the ecliptic in 1 is formally defined by the orbital angular momentum vector, the long term against the sky more stable than the Earth's orbit, which is subject to perturbations by the other planets.

The direction of rotation of the coordinate system, ie positive values ​​of the variables follow the usual conventions of physics ( three- finger rule ), with the north celestial pole as a priority excellent point.