Ecliptic coordinates of a direction
The ecliptic coordinates of a direction are the coordinates of the direction referred to the mean ecliptic and the origin direction of this plane defined by the equinox. These coordinates are called true when they are referred to the mean ecliptic equator and the true equinox of the date, mean of the date when they are referred to the ecliptic and mean equinox of the date, and mean of a reference date when they are referred to the mean ecliptic and equinox of that reference date. (See True coordinates and Mean coordinates). Two kinds of ecliptic coordinates are used: Cartesian ecliptic coordinates and polar ecliptic coordinates with celestial longitude and latitude.