My brain is going back to 9th grade earth science with this one…Astronomical autumn begins with the autumnal equinox on September 22 in the U.S. I will be in Manhattan for that. Meteorological autumn, which meteorologists use for record-keeping, started September 1 and runs through November 30. I was in Amsterdam for that. Meteorological seasons are built for convenience, while astronomical seasons follow Earth’s orbit. Meteorological seasons simply group whole calendar months into three-month blocks: autumn is September through November, winter is December through February, and so on. Every season starts on the 1st of a month. No single person is credited with creating this system. It seems to have emerged gradually from the practice of weather services and climatologists, who needed consistent three-month blocks for record-keeping. The convention is now standard at national weather services like NOAA and the UK Met Office, and it’s used in the World Meteorological Organization’s climate reporting. The underlying idea is much older. Grouping months into seasons by temperature, rather than by the sun’s position is a natural fit for anyone tracking weather data, so it likely developed in stages rather than from one invention.
By contrast, astronomical seasons are set by the sun’s position, which is to say, equinoxes and solstices. I’m not sure I ever realized the difference, but both are moments defined by Earth’s tilt relative to the sun, but they mark opposite extremes. An equinox occurs in March and September when the sun is directly above the equator, so day and night are nearly equal everywhere on Earth (the word literally means “equal night”). It marks the start of spring and autumn. A solstice happens in June and December when one hemisphere is tilted as far toward or away from the sun as it gets. The June solstice gives the Northern Hemisphere its longest day and the start of summer, while the December solstice gives it the shortest day and the start of winter. The Southern Hemisphere is reversed. The word means “sun stands still,” because the sun’s noon height stops climbing or dropping briefly before reversing. So, equinoxes are the halfway points, with balanced light, and solstices are the extremes, with the most or least daylight.
Because Earth’s orbit is slightly elliptical and the calendar doesn’t line up perfectly with it, the seasons vary in length (autumn is about 89.9 days, for example) and the start dates shift by a day or so from year to year. Meteorologists and climatologists prefer the consistency of meteorological seasons because it makes statistics easier. Comparing seasonal temperature and precipitation across years is much simpler when every season has the same predictable start date and nearly the same number of days. It also fits the weather better. Temperatures lag behind the sun, since land and oceans take time to heat and cool. The solstice is the sun’s peak, yet the hottest weather usually comes weeks later, so the meteorological summer (June-August) tracks the warmest three months in the Northern Hemisphere more closely than the astronomical one does.
We all tend to get somewhat sentimental about autumn for some reason. Autumn is best known for transitional things. To begin with, there are the changing leaves (particularly prevalent in my old stomping grounds of the Northeast). As days shorten, trees stop producing chlorophyll, revealing the reds, oranges, and yellows underneath before the leaves drop. That’s why it’s also called “fall”…Duh! That’s accompanied by cooler weather with temperature drops, humidity easing, and frost beginning in many regions. Harvest is a big part of autumnal thinking. It’s the traditional time for gathering crops, which is why the harvest moon, harvest festivals, and Thanksgiving are tied to it. A good autumn harvest has always been essential for surviving the rigors of winter. Shorter days as daylight shrinks steadily toward the winter solstice, and in many places clocks go back an hour, highlighting that shortening. In the U.S. its also back to school season. The seasonal traditions of autumn include pumpkins, apple picking, Halloween, football season, and cozy foods and drinks like cider and pumpkin spice. Animals are less sentimental and more pragmatic with birds migrating, and animals like squirrels stockpiling food or bears fattening up for winter and their hibernation.
I rarely meet anyone who doesn’t like autumn. There is a sort of comfort imbedded in it after a long hot summer and before a long cold winter. The relief from the heat and crisp air feels refreshing, and it’s comfortable for being outdoors. The visual beauty of fall foliage is striking, and the low, golden light adds to it. There is a cozy appeal to wearing sweaters, drinking warm drinks, and baking that are all enjoyable in a way they aren’t in summer heat. Add to that the traditions and gatherings that take place at this time of year. Halloween has gone global, Thanksgiving is getting celebrated in places that have no turkeys or pumpkins, harvest festivals exist when the only one picking produce is a machine, and football season gives the season a lot of shared, communal events…regardless of where you are in the world. Because of the school calendar, September often feels like a reset, with new routines and goals, more so than January for many people. Many people associate autumn with childhood memories, which makes the season emotionally sticky. There’s also a strong cultural feedback loop. Seasonal marketing, social media, and pumpkin-spice everything reinforce the idea, which makes it feel even more universal than it is. For some people, shrinking daylight makes autumn a harder season, but they have to just keep quiet while everyone else is rolling in the leaves.
Being in NYC rather than on my hilltop for this seasonal equinox is bringing all of this to mind. The temperature is expected to be in the mid-60s, so cool, but not unpleasant. The skies will likely be steel grey with a touch of rain, which will feel equally appropriate and almost refreshing after the hot summer we’ve all had. In addition to the work I am going for (expert witness workshops with major litigation firms), I am seeing old friends and going out to Brooklyn to watch granddaughter Evelyn give a speech for a school environmental day. It all feels like a perfect way to usher in the new season.