What is the astronomical significance of this moment?  At this moment the Sun in its apparent path around the sky will stand directly over the equator of the Earth.  It is one of two times during the year when this happens, the other being on the first day of Autumn.

These are the two days of the year when the Sun is above the horizon for exactly half the day and is below the horizon an equal amount of time.  Thus, the length of daylight is equal to that of the night (neglecting twilight and atmospheric refraction) and this day is termed the equinox from the Latin for “equal night.”  After the equinox in March, called the spring or vernal equinox, the hours of daylight continue to lengthen with the Sun above the horizon for a longer time each day.  This continues until the summer solstice in June (This year at 7:59 p.m. EDT June 20).  Following the solstice the days get shorter until at the fall or autumnal equinox (next at 11:44 a.m. EDT on September 22) the day and night are once again equal in length.

Since on the vernal equinox the Sun stands directly above the Earth’s equator, folklore holds that one is able to stand an egg on its end on that day.  This old wives’ tale is true; one can stand an egg on its end on that day!  However, the tale is only a half truth because, in fact, one can stand most eggs on their ends any day of the year, not just on the vernal equinox.  Try it!  (It really depends on the egg, not the day of the year.  Some eggs can be balanced on their ends easier than others depending on the position of the yolk, and thus the center of gravity, within the egg itself.)

About PARI

PARI is a not-for-profit public foundation established in 1998.  Located in the Pisgah Forest southwest of Asheville, NC, PARI offers educational programs at all levels, from K-12 through post-graduate research.  The institute is affiliated with the 16-campus University of North Carolina system through PARSEC, a UNC Center hosted at PARI, and is a member of the NC Grassroots Museum Collaborative.  For more information about PARI and its programs, visit www.pari.edu.