autumnal equinox definition by American Heritage Dictionary
nounThe American Heritage® Dictionary of the English Language, 4th edition Copyright © 2010 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
- The point at which the ecliptic intersects the celestial equator, the sun having a southerly motion.
- The moment at which the sun passes through the autumnal equinox, about September 23, marking the beginning of autumn in the Northern Hemisphere.
autumnal equinox - Science Definition
See under equinox.