FIELD NOTES BLOG

Defining Seasons

Jillian Neece
January 25, 2024

 Defining Seasons


Now that winter has arrived in full force, I’m sure many people are wondering when warmer temperatures will be gracing us with their presence again. Don’t get me wrong, there are plenty of fun outdoor activities to enjoy in the winter like sledding, skiing, and winter hiking, but when temperatures are as cold as they have been, I can’t help but look forward to spring. That led me to wonder: When does spring officially start? After doing some research, I realized that the answer is not as straightforward as it might seem.

 

 

Seasons can be tricky because there are two popular ways of defining them: the astronomical way and the meteorological way. Astronomical seasons (think astronomy; the movement of planets) are distinguished based on where the Earth is on its orbit around the sun. This method uses the dates of equinoxes (when day and night are equal lengths) and solstices (the longest and shortest days of the year) as transitions between the four seasons. Any time after the winter solstice (December 21st or 22nd) but before the spring equinox (March 19th, 20th, or 21st) is considered winter, and so on.

 

using the astronomical definition, each season begins with a solstice or equinox, meaning the calendar date of the season’s beginning may vary each year.

 

Since the Earth’s orbit around the sun is not a perfect circle, there is some variation in the length of the seasons and on which calendar day the seasons will begin. This can make it difficult for scientists and weather forecasters to compare weather and climate information between different years. Weather from some day in 1990 might not actually be comparable to that same calendar date in 2024 if the Earth was in a slightly different place in its orbit. Thus we needed a different way to track the seasons that is more relevant to our human activities. Enter: meteorological seasons!

 

Meteorological seasons (think meteorology; forecasting weather) are grouped together in three-month blocks based on average temperatures. Instead of including only the last ten-ish days of December in the official definition of winter like the astronomical method would, meteorological winter includes all of December, January, and February, since those tend to be the coldest months of the year.

This way of classifying seasons is much easier to work with when predicting things like weather and crop schedules because there is less year-to-year variation in the length of seasons. The length of seasons always stays the same, with the only exception being leap years , when winter is one day longer. Meteorological seasons also match better with our standard calendar since it’s able to be broken down into full months, allowing us to say things like, “students don’t have classes in the summer” instead of, “students don’t have classes during the last third of spring and the first two-thirds of summer.” That would be quite the mouthful!

Using the meteorological definition, each season begins on the first of the month.

Additionally, meteorological seasons surround the solstice and equinox, including some time before those astronomically significant days and some time after them. So while the astronomical seasons would consider the warm days of mid-June to be spring (because the summer solstice doesn’t occur until around June 20th), the meteorological seasons recognize all of June as a summer month because it has some of the warmest yearly temperatures.

Both of these ways of defining seasons have value, which is why we keep them both around! For the average person, the meteorological seasons are more comprehensible because they follow the calendar that we are familiar with and are distinguished by something we all experience: temperature. Astronomical seasons, on the other hand, give an important context for why our temperatures vary throughout the year the way they do. Most ancient calendars were based on the astronomical seasons because there were clear and measurable events (namely the solstices and equinoxes) that signaled the change of seasons.

Whether you want to use the meteorological definition or the astronomical definition of spring, we still have a few weeks of winter before we should start expecting warmer temperatures and ephemeral flowers popping up. So instead of spending our time longing for the green leaves of spring, let’s choose to take advantage of the short-lived beauty of snow lining the trees! There are plenty of ways to stay active and connected to nature, even when it’s cold. Be sure to check out our events calendar to see how you can stay connected to people and nature this winter!

RECENT ARTICLES

September 3, 2025
As the summer camp season comes to a close, creek shoes are dried, crayons are put away, and our staff reflect on their summer of directing and supporting Severson Dells camp. This summer, they led and assisted with 9 weeks of summer camp programs that reached 211 campers! Out of the many adventures this season, here are some of their highlights and what they learned along the way.
By Emma Zimmerman August 26, 2025
When I started at Severson Dells nearly two years ago, I never would have believed I’d still be here today. What was supposed to be a short detour turned into one of the meaningful positions I have served. These years have flown by, and as I sit down to write this farewell, I keep circling back to my early days here. It feels important to revisit that beginning, because in so many ways, it shaped everything that followed.
By Shannon Osadjan August 26, 2025
While my time at Severson Dells is coming to an end, my time and experience as a junior naturalist is just beginning. When I accepted this job position, I was a recent college graduate who was ready to get into the environmental work force but didn’t know where to start. Here I am, a year later, and I feel ready and excited to take on whatever comes my way. Last September, when I first started working here at Severson Dells, I didn’t know what to expect. I had never been an educator before and I was nervous about my skill-set, but I pleasantly surprised myself. I found myself enjoying teaching, and the goofy experiences and questions that came with it. When I started here, my biggest goal for myself was to become better informed about the ecology of Rockford, and being more aware and able to identify what’s growing around me. A year later, I am proud of myself and how much I have learned. Because of my schooling background being in geology, I already had a familiarity with looking at the outside world in a different lens. I know how to look at the geology and the basic layout of an area to understand the depositional environment, or what the land most likely looked like back in the day. However, being at Severson Dells for the past year has shown me how to appreciate nature and the outdoors in a new way, in a biological sense. I now know how to look at the ecology of an area and see how the plants are working together, and how this compliments what the birds and the bugs are doing, and how the trees play a role too, and this cycle keeps going. I knew forests were interconnected, but I feel like I truly get it now. It’s helped me to connect the pieces of nature that I wasn’t aware of before, and put them all together now to see a new, bigger picture. Severson Dells is a place I will always hold dearly to me. The experiences I had, the challenges I overcame while being here, and the personal growth I’ve been able to experience: all of this helps shape my love for this lovely forest preserve here in Northern Illinois. I want to be sure to express my appreciation for the staff here at Severson Dells Nature Center, and the kindness they always treat everyone with. The people here are always so willing to help me with learning new skills, diving into intimidating science topics, and trying to help foster that curiosity that everyone has inside of them. As I close this chapter, I feel inspired and grateful for the connections I’ve made, and ready for what the future has in store for me.