Les Jones

Science > First Day of Spring

Today is officially the first day of spring, also known as the spring equinox or vernal equinox.

So what does that mean? It means that the sun's position above the horizon today is at a mid-point between the winter solstice and summer solstice. The sun's highest position of the day is lowest at the winter solstice, and highest at the summer solstice. (In this article about our trip to Asheville in December I mentioned that the long shadows in the pictures were caused by the sun's low position.)

People often say that the equinoxes are the days when daytime and night time are equal. That isn't exactly right, though there is a relationship. That's true at certain latitudes, but not others. The winter and summer solstices are also near the longest and shortest days of the year, again depending on your distance from the Earth's equator. The real definition for these events is determined by the sun's position in the sky.

The spring equinox is usually March 21st, and occasionally March 22. 2004 is a leap year. The extra day in February caused the equinox to fall on the 20th. According to my non-computer calendar, the remaining equinox and solstice dates this year are:

Summer Solstice - June 20
Autumnal Equinox - September 22
Winter Solstice - December 21