Ecliptic coordinate system
The
ecliptic coordinate system is a
celestial coordinate system that uses the
ecliptic for its fundamental plane. The ecliptic is the path that the
sun appears to follow across the sky over the course of a year. It is also the
projection of the Earth's
orbital plane onto the
celestial sphere. The
latitudinal angle is called the ecliptic latitude, and the
longitudinal angle is called the ecliptic longitude. Like
right ascension in the
equatorial coordinate system, the zeropoint of the ecliptic longitude is the
vernal equinox.
What do you think such a coordinate system would be useful for? If you guessed charting solar system objects, you're right! Each of the planets (except Pluto) orbits the sun in roughly the same plane, so they always appear to be somewhere near the ecliptic (i.e., they always have small ecliptic latitudes).
This article originates from Jason Harris' Astroinfo which comes along with KStars, a Desktop Planetarium for Linux/KDE. See " class="external">http://edu.kde.org/kstars/index.phtml