Vernal Equinox

It sure has felt like spring in the Peoria area lately, with warming temperatures and signs of growth all around us. Daffodils and lilies are emerging in my yard. These signs of new life are very welcome after a long cold winter. The official beginning of spring is just days away, on March 20, at 5:45 PM CDT! 

I like to imagine she is greeting the spring sunrise. Woman Before the Rising Sun, Casper David Frederich, 1818.

The beginning of spring is marked by the vernal equinox, which along with the autumnal equinox is one of two days of the year that we have an equal amount of day and night. What causes this change of day length and season? The Earth's orbit and tilt, of course! Here is a review of what I wrote for the autumnal equinox:

Both spring and fall start with the equinoxes, the two days of the year when there is an equal amount of daylight and nighttime.  We have solstices and equinoxes (or in other words, seasons) because of the Earth's tilt on its axis.  As the Earth orbits the Sun, usually one hemisphere is tilted toward the Sun while the other is tilted away. When the Northern Hemisphere is tilted toward the Sun and it is summer, the Southern Hemisphere is tilted away and is in winter, and vise versa. The equinoxes occur when the Earth is at a point in its orbit where both hemispheres get equal amounts of sunlight - neither is tilted more towards the Sun than the other. On the equinox, the Sun rises due east, and sets due west, giving everyone equal amounts of day and night. 

Illumination of the Earth at different seasons. Notice that on the equinoxes, both hemispheres receive an equal amount of sunlight. Image credit: Wikipedia Commons.

 

The Sun's path across our sky gives us longer days in the summer and shorter days in the winter. On the Equinoxes, day and night are equal! Image credit: Daniel V. Schroeder

Hourly images of the Sun were captured in Bursa, Turkey, on key days from solstice, to equinox, to solstice. The lower path is shorter and in winter, the higher path is longer and in summer. The middle path is spring or fall. Image credit: APOD and Tunc Tezel

Perhaps you have already noticed the days getting longer since the winter solstice. Spring is always the most cheerful time of the year for me, because each day will get a little longer until the summer solstice on June 21. Soon the trees will be budding and it will be gardening time again. 

I hope you have a very joyful vernal equinox. Celebrate by getting outside and enjoying the beautiful weather (perhaps by running a race?!). Or visit us here at the Dome Planetarium to learn more about the Sun's path through our sky, and how to identify winter and spring constellations. Find our schedule and show descriptions here. 

http://www.peoriariverfrontmuseum.org/dome-planetarium/5k-race