The short days of winter are starting to fade away as the days continue to lengthen. And next Wednesday, March 20, is the spring equinox.
The fall and spring equinoxes occur when the sun passes directly overhead on the equator. There will be 12 hours and 11 minutes between sunrise and sunset in Bismarck on the 20th. Compare that to a little over eight hours between sunrise and sunset last December on the winter solstice.
If the earth’s rotation was perpendicular to the plane of its orbit, we wouldn’t have much variation in seasons. But the earth is tilted on its axis by 23 1/2 degrees. As a result, variations in the directness of the sunlight hitting the earth vary throughout the year, giving us the seasonality here in temperate zones.
The days will continue to lengthen until the summer solstice, which this year will occur on June 22, when there will be a whopping 15 hours and 51 minutes of sunlight. After that, of course, the days shorten until the winter solstice in December.
North Dakota has at least two structures for celebrating the equinoxes and solstices:
- North of Bottineau is Mystical Horizons (pictured above). There are stone structures to mark the equinoxes and solstices as well as a sundial, a structure for viewing the north star (at night of course), and an information kiosk.
- South of Valley City State University, near the interstate, is a Medicine Wheel that can be used to observe the cycles of the seasons. The site also has a Meridian Calendar and a Walking Tour of the Solar System.