THE AUTUMNAL EQUINOX
(September 1, 2010) – Astronomers at the Pisgah Astronomical Research Institute point out that at 11:09 p.m. EDT on Wednesday, September 22 the Sun will cross the celestial equator in the sky heading south. This will be the first moment of autumn.
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 spring. 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 this day is termed the equinox from the Latin for “equal night.” After the equinox in September, called the autumnal equinox, the hours of daylight continue to shorten with the Sun above the horizon for a shorter time each day. This continues until the winter solstice in December (This year at 6:38 p.m. EST on December 21).
Following the solstice the days get longer until at the spring or vernal equinox (next at 7:21 p.m. EDT on March 20), the day and night are once again equal in length. About PARI The Pisgah Astronomical Research Institute (PARI) is a not-for-profit 501 (c)(3) foundation established in 1998. Located in the Pisgah Forest 30 miles southwest of Asheville, NC, the PARI campus is a dark sky location for astronomy and was selected in 1962 by NASA as the east coast tracking station for manned space flights. Today, the 200 acre campus houses radio and optical telescopes, earth science instruments, 30 buildings, a fulltime staff and all the infrastructure necessary to support STEM (science, technology, engineering and math) education and research. 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.Read the full article