‘Spring fever’ is in the air, and snow isn’t, as the equinox occurs Thursday in Philly

Humans have imposed an artificial order on the meteorological seasons. They play games with the clocks. They historically have applied creative accounting to the calendars. They have tried mightily to convince consumers that Halloween begins in August, and Christmas in September.

But, so far at least, astronomy has remained above human tinkering, and at 5:01 a.m. Philadelphia time Thursday the sun beamed its most direct light on the equator, on its way to turning up the heat in the Northern Hemisphere, and the real spring will have arrived.

To honor the season when — in Tennyson’s famous words — “a young man’s fancy lightly turns to thoughts of love,” here are a few observations.

As it happens, a young or older person’s fancy may turn more than lightly to thoughts of love and other things, according to mental health experts who hold that “spring fever” is a real phenomenon. It “aptly describes a feeling that seizes you with its urgency and impulses,” observed psychiatrist Norman Rosenthal, based in Bethesda, Md., who pioneered research on seasonal affective disorder. Another expert defined it as “a rapid and yet unpredictable fluctuating mood and energy.” For some it isn’t all blossoms and songbirds.

(The subject of that Tennyson poem, “Locksley Hall,” may well have been a victim: After those oft-quoted words, the rest of the poem is a not-always-uplifting treatise on lost love and the state of the planet in the 19th century.)

But for most people, spring fever is harmless. It is “not a medical term and may be a normal response to longer days and warmer temperatures,” said John Lauriello, a psychiatry professor at Thomas Jefferson University. In some instances, spring fever might even result in more-organized closets.

For those who find winter about as pleasurable as filling out tax forms, the triumph is yours. For snow-lovers, you might console yourself with the Phillies spring-training coverage on our website.

While the three-month “meteorological winter” ended Feb. 28, it has snowed after the equinox on average about every other year, according to an Inquirer analysis of records dating to 1885. Next month marks the 110th anniversary of the 19.9-inch Easter blizzard in Philly. But that accounted for 14% of all post-equinoctial snows in Philly. The overall annual average comes to about an inch. And this year not even a decent threat is out there.

The analysis, by the way, honored strict astronomical purity. Thus, for the historically disruptive “equinox storm” of March 19-21, 1958, the 11 inches of snow that accumulated at Philadelphia International Airport before the equinox occurred at 11:06 p.m. on March 20 weren’t counted.

Calendars are ingenious, pegged to Earth’s annual 574.4 million-mile orbit around the sun. They also are imperfect, and the sun doesn’t think much of them. That annual voyage takes 365.24219 days, by NASA’s count, which is why leap year has occurred every four years since the reign of Julius Caesar, and that has affected equinox dates. Life would have been simpler if the journey was precisely 365.25, but through the centuries, the spring equinox had slipped from March 23 to March 11. In the 1500s, Pope Gregory calculated that skipping leap years in century years that were not divisible by 400 — 1900, 2100, for example — would correct that problem, and that’s the system we have today. It’s not precise, but the U.S. Naval Observatory says it will take 3,300 years before it’s off by a whole day.

On March 1, the time between sunrise and sunset was 11 hours, 20 minutes. On Sunday — yes, four days before the equinox — the split was 12 and 12. By month’s end, it will be 12 hours and 38 minutes.

If any snow happens to fall, it won’t live long. The sun’s wattage above Philly is 73% stronger than it was at the winter solstice and close to what it will be on Sept. 20.

It would be natural to perceive that spring is a shade behind schedule this year, said Anthony Aiello, the associate director at Longwood Gardens. For a change, however, he said it’s pretty much right on schedule after a winter of near-normal temperatures that made it the coolest December-through-February period in a decade. “I think we are used to seeing things earlier,” he said.

But it’s happening. “Some of the early magnolias are opening up,” he said. The daffodils, crocuses, and witch hazel are in full bloom, he said, and cherry blossoms are starting to pop on the Philly urban heat island. Red and silver maples are flowering.

Few colors on Earth are as inspiring as those first delicate greens of the new leaves, but don’t miss out on the greatly underrated bud season. The trees are about filled to the brim with them, and they especially are evident in the golden-reddish sunset light. They are at once visible, yet subtle enough that they don’t block out the sunlight.

The leaves will have their day, and next month’s full moon, April 12, will be a last chance to see the unobstructed moonlight through the trees. But that silvery moonlight on the new leaves in May is quite a consolation prize.