An Introduction to Solar System Astronomy
Prof. Richard Pogge
The Celtic Solar Calendar and traditional Japanese Luni-Solar Calendars used the cross-quarter days to mark the start of the various seasons, unlike the current tradition in the West where we say speak of the Equinoxes and Solstices proper as the first day of their respective season. The Celtic and traditional Japanese usages are actually more astronomically correct, at least for the latitudes of those societies. For example, in the traditional Japanese calendar the first day of spring (Risshun) is on the first cross-quarter day (Feb 3 or 4 - time of the traditional Setsubun festival which used to mark the beginning of the new year), Summer begins on May 6 (Rikka), autumn on August 8 (Risshuu), and winter on November 7 (Ritou).
In 2007, the approximate times of the cross-quarter days are as follows (all times are UTC):
1st CQD 2007 Feb 4 05:18 UTC 2nd CQD 2007 May 5 21:21 UTC 3rd CQD 2007 Aug 7 21:31 UTC 4th CQD 2007 Nov 7 19:24 UTCThese were computed using data provided by the JPL Horizons On-Line Ephemeris System to compute the ecliptic longitude of the Sun as seen from Earth (geocentric). Times are rounded to the nearest minute.