Spring arrives at the moment of ‘equal night’

Spring arrives at the moment of ‘equal night’
John C. Lorson

The nesting schedule of these Canada geese, who have chosen the fine architectural work of a family of Holmes County muskrats as the foundation of their new home, is driven more by photoperiod — the length of daylight in each day — than weather or even the availability of other resources.


My youngest daughter was born on the first day of spring, March 21, many years ago. It was a happy coincidence that seemed to jibe nicely with the earthy name we had already chosen for her: Sylvia.

In Roman mythology “Silvia” was the goddess of the woods. And what joyful thought of spring doesn’t include the rebirth of the forest? I figured we could always happily observe both our daughter’s birthday and the birth of a new season on the very same day each year. Turns out I was wrong!

The following year the first day of spring would arrive a day earlier than the previous year. In mild befuddlement I set about my research only to find that it would be over 100 years until the vernal equinox once again fell on Sylvia’s birthday.

The science behind all of this begins with the very origin of the word equinox, which in Latin means “equal night” when we experience 12 hours of daylight and 12 hours of darkness. The equinox occurs when the sun is situated directly over the equator, resulting in an even split of daylight and darkness across the profile of the globe. The earth experiences two such equinoxes each year. The vernal (Latin for “of the spring”) equinox falls annually within the span of March 19, 20 and 21, and the autumnal equinox (no translation required) falls on Sept. 22, 23 or 24.

There are a number of different ways to envision this moment of “equal night.” The simplest I can think of without having a model to demonstrate is this: If you were standing at the center of the sun, looking out at the earth at the moment of the equinox, you would be able to see the full 23.5-degree tilt of the Earth’s rotational axis. Equal amounts of sunlight would be bathing the northern and southern hemispheres.

It would be really glorious, I’m sure, and you would think, “Wow, John was right!” Next, of course, you would be vaporized into subatomic particles by the 27 million degree temperature at the core of the sun, but it would have been an amazing moment of clarity.

All of this, of course, is brought to us compliments of the earth’s annual trip around the sun, which takes exactly 365 1/4 days. It’s those pesky quarter days and the Leap Day that gathers them all together once every four years, that trips us up when it comes to aligning the equinox with the calendar. That’s how we end up with a range of days upon which the equinox can fall within a given calendar year.

Sometimes even the best efforts of man fall short at defining the actions of nature. (Which may very well be the case with this particular column.)

This year the vernal equinox actually falls on March 19, marking the earliest arrival of spring in 124 years.

The natural world needs no reminder that it’s time to awaken and get growing. Animals and plants track photoperiod, or amount of daylight in a 24-hour cycle, much more closely than we humans and our fancy calendars. Photoperiod triggers the “on” and “off” switch to thousands of complex actions in nature from bird song, to the budding and growth of plants, to hormone production and mating activity in animals.

The increasing amount of daylight between now and the summer solstice — the longest day of the year — will bring changes all around the natural world. Be sure to get out there whenever you can and watch nature as it unfolds — and don’t forget to write me with your questions!

Write with comments or questions about the natural world to The Rail Trail Naturalist, P.O. Box 170, Fredericksburg, OH 44627, or email jlorson@alonovus.com.

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