March 20 (UTC) - the same date is the "vernal equinox" in the Southern Hemisphere.
The "Vernal Equinox" is the beginning of "Spring" and the end of "Winter". The Autumnal Equinox is the beginning of "Autumn" or "Fall" and the end of "Summer". In the Northern Hemisphere, the Vernal Equinox is in March and the Autumnal Equinox in September each year.
No, it moves slightly forwards and backwards in time, but within a 12 hour period due to the Earth's wobble that is separate from the Procession of the Earth's poles. So in some years it can occur on the 20th of September, and other years on the 21st.
The Autumnal Equinox will occur in the northern hemisphere, this year on September 22nd at 10:49am EDT.
September 22
The summer solstice occurs around December 21st, while the winter solstice occurs around June 21st in the southern hemisphere. The vernal equinox occurs around September 22nd, and the autumnal equinox occurs around March 20th in the southern hemisphere.
the vernal equinox is always on the 21 of march. that's the day I'm righting this. _______________________________ The equinoxes occur on March 21 and September 21, plus or minus one day because of the cycle of leap years. In the northern hemisphere, the vernal equinox is in March, and the autumnal equinox is in September; in the southern hemisphere, it's reversed. In 1978, the vernal equinox in the northern hemisphere was March 20, 1978 at 5: 10 PM GMT.
The exact time of the vernal equinox varies from year to year. This year, the March equinox (the vernal equinox in the northern hemisphere, the autumnal equinox in the southern hemisphere) will occur on March 20, 2010 at 17:32 GMT. The web page below is the "Earth's Seasons" web page from the U.S. Naval Observatory.
November
Yes, equinoxes occur simultaneously in both the Northern and Southern Hemispheres. During an equinox, the sun is positioned directly above the equator, resulting in nearly equal day and night lengths across the globe. This phenomenon happens twice a year, around March 20 (vernal equinox) and September 23 (autumnal equinox). Thus, both hemispheres experience the equinox at the same moment.
The December Solstice occurs in December. It marks the shortest day and longest night of the year in the Northern Hemisphere and the longest day and shortest night in the Southern Hemisphere. The Equinox occurs around March and September when day and night are of equal length.
Equal hours of daylight and sunlight occur on a day known as the Equinox. There are two of these days every year - a vernal Equinox (in the spring), and an autumnal Equinox (in the fall). This answer is easily searchable on this website. Please refer to the search function before posting a question like this in the future. Source: My own personal knowledge.
The autumnal equinox 2009 will occur on September 22 at 21:18 UTC.To find out what time that is for you, please see http://www.timeanddate.com/worldclock/converter.html September 22, 2009 5:18 PM EDT according to the International Campaign For Tibet 2009 Calendar