At what two celestial locations do the celestial equator and eliptic coincide?

The two points where the where the celestial equator cross the ecliptic are called the vernal (or spring) and autumnal equinox. This is in relationship to the northern hemisphere but the names are retained in the southern hemisphere. The vernal equinox occurs around March 20 or 21st and the autumnal equinox occurs around September 22 or 23. These are the times the sun passes through these points on its way north or south. There is a variation because there are about 365 1/4 days in a year so the calendar must be adjusted by a full day once every four years (leap year). This leads to a change in time from year to year of a quarter of a day which is brought back into line by the extra day in the leap year. There is a further adjustment as the equinox varies by one day each century, another by a day in 400 years and another by a day every 4000 years. Our current calendar is designed to keep the vernal equinox on March 21st.