Spring Equinox

Today is the Spring Equinox

Today we welcome spring! (Astronomical Spring). Today is the Spring or Vernal Equinox.

The sun is directly overhead at solar noon at the Equator today.

“Equinox” means “equal night” and on the Vernal and Autumnal Equinoxes, there is equal day and night over the entire Earth. Now, if you see the sunrise and sunset for today (7:47 a.m. and 7:54 p.m. for Grand Rapids), you’ll note that the day is not exactly 12 hours. It’s 12 hours and 7 minutes.

There’s two reasons for that. First, we don’t measure sunrise and sunset from the middle of the sun. Sunrise is when the top tip of the sun first appears over a totally flat horizon. Sunset is when the last or top tip of the sun disappears over a totally flat horizon. The second reason is that light bends a little when it enters the Earth’s atmosphere.

From March 11-24 daylight increases the fastest, at 2 minutes and 56 seconds each day. This week, we’ll gain 20 minutes and 32 seconds of daylight.

The spring equinox can occur on March 19, 20 or 21. It’s usually on the 20th.

The last time the March equinox was on March 21 (in UTC – Universal Time Coordinate – in the military is may be referred to as “Zulu” was in 2007. It will happen again in 2101.

Due to time zone differences, the equinox may occur a day earlier at locations that are behind UTC. (four hours ahead of EDT). Take the example of mainland United States. While locations following UTC saw a March 21 Equinox in 2003 and 2007, there is no March 21 equinox in mainland US in the 21st century!

Between 2020 and 2048, March 19 equinoxes will happen every leap year in Central, Pacific, and Mountain time zones in the United States. In the same period, the years between the leap years will see a March 20 equinox.