Pasachoff, Jay M. Hopkins Observatory, Williams College, Williamstown, Massachusetts.
- Related Primary Literature
- Additional Reading
One of the two places in the sky where the ecliptic crosses the celestial equator; or one of the two times of the year when the Sun crosses these points. The ecliptic is the great circle across the sky that marks the mean path of the Sun; the celestial equator is the great circle that is an extension into the sky of the Earth's mean Equator. These two great circles meet at two points, one of which is the vernal equinox and the other the autumnal equinox. The Sun passes the vernal equinox each year about March 20, and the autumnal equinox about September 22. The vernal equinox can occur as early as March 19 and as late as March 21; for most of the twenty-first century it will be on March 20. The autumnal equinox can occur as early as September 21 and as late as September 24; for most of the twenty-first century it will be on September 22. The dates and times drift with the difference between the actual solar years and 365 days, and are corrected by leap years. This results in a 4-year variation superimposed on a negative 11-min-per-year slope (illus. a and b). Since 2000 was an ordinary leap year in the Gregorian calendar, unlike 1900, the dates will continue to decline through 2100 (illus. c). See also: Astronomical coordinate systems; Calendar; Time
The content above is only an excerpt.
for your institution. Subscribe
To learn more about subscribing to AccessScience, or to request a no-risk trial of this award-winning scientific reference for your institution, fill in your information and a member of our Sales Team will contact you as soon as possible.
to your librarian. Recommend
Let your librarian know about the award-winning gateway to the most trustworthy and accurate scientific information.
AccessScience provides the most accurate and trustworthy scientific information available.
Recognized as an award-winning gateway to scientific knowledge, AccessScience is an amazing online resource that contains high-quality reference material written specifically for students. Contributors include more than 9000 highly qualified scientists and 43 Nobel Prize winners.
MORE THAN 8700 articles covering all major scientific disciplines and encompassing the McGraw-Hill Encyclopedia of Science & Technology and McGraw-Hill Yearbook of Science & Technology
115,000-PLUS definitions from the McGraw-Hill Dictionary of Scientific and Technical Terms
3000 biographies of notable scientific figures
MORE THAN 19,000 downloadable images and animations illustrating key topics
ENGAGING VIDEOS highlighting the life and work of award-winning scientists
SUGGESTIONS FOR FURTHER STUDY and additional readings to guide students to deeper understanding and research
LINKS TO CITABLE LITERATURE help students expand their knowledge using primary sources of information