Ecclesiastical full moon a transliteration of the Aramaic word meaning Passover. The date of Easter is determined as the first Sunday after the "paschal full moon" falling on or after March 21 (the ecclesiastical fixed date for the Spring Equinox; the actual Equinox can fall on March 19, 20 or 21). This "full moon" does not currently correspond directly to any astronomical event, but is instead the 14th day of a lunar month, determined from tables. It may differ from the date of the actual full moon by up to two days. The use of tables instead of actual observations of the full
Equinox zero. Its latitude will not be exactly zero, since Earth is not exactly in the plane of the ecliptic. Its declination will not be exactly zero either. (The ecliptic is defined by the barycenter of Earth and the Moon combined.) The modern definition of equinox is the instants when the Sun's apparent geocentric longitude is 0° (northward equinox) or 180° (southward equinox). See the adjacent diagram. Because of the precession of the Earth's axis, the position of the vernal point on the celestial sphere changes over time, and the equatorial and the ecliptic coordinate systems change accordingly. Thus when specifying