Vernal Equinox

• ‹ Previous program
• 79 of 1968
• Next program ›

Spring is arriving in the northern hemisphere today. The Sun crossed the equator into northern skies at 12:48 a.m. Central Daylight Time -- the moment of the vernal equinox. The days will continue to grow longer until the summer solstice in June.

In ages past, the vernal equinox was often considered the most important day of the year in the northern hemisphere. Life was returning to the landscape after the winter months, and it was about time to plant crops -- a good day to celebrate.

In fact, the equinox was so important that in many cultures, the time around the equinox marked the beginning of the new year. That includes western Europe -- and especially Great Britain and its American colonies, where until 1752, the year began on March 25th.

Astronomers adopted the vernal equinox as the start of the celestial year. They use a coordinate system with lines of right ascension and declination -- the equivalent of longitude and latitude on Earth. The starting point for this system is the Sun's location at the moment of the vernal equinox -- celestial coordinates zero, zero.

Thousands of years ago, the vernal equinox took place when the Sun was passing through Aries, the ram, so the equinox is sometimes called the First Point of Aries. But Earth wobbles on its axis a bit, so the Sun shifts a bit with respect to the stars. So today, the Sun is actually one constellation over at the equinox -- near the western edge of Pisces.

Script by Damond Benningfield, Copyright 2008

For more skywatching tips, astronomy news, and much more, read StarDate magazine.