On a sizzling solstice day in Philly, 10 things to know about the longest days — and season — of the year

To an overly warm welcome, the astronomical summer arrives in Philly at 4:50 p.m. Thursday, when for an immeasurable instant the sun will laser its light directly over the Tropic of Cancer, its northernmost intrusion of the year.

Lovers of daylight, this is your time. The sun won’t be setting before 8:30 p.m. until July 15, almost as though it is unwilling to yield the sky to the ponderously creeping darkness. And for the next few nights, the darkness will be getting a challenge from the east with the rising of the full “strawberry moon.”

Forecasters say Philadelphia may see 100 degrees this weekend for the first time in a dozen years, but ‘tis the season when torpor is acceptable, if not expected; when the strawberries, tomatoes, and peaches are plentiful; and when insects sing and light up the night.

Here are 10 things to ponder about the solstice and the days and nights to follow.

Solstice comes from the Latin words for “sun” and “stand.” That direct solar beam eventually will migrate 3,200 miles south to the Tropic of Capricorn in December, but for now it’s not moving much. Thursday technically is the longest day with 15 hours, 3 minutes, and 47 seconds between sunrise and sunset, but it beats Friday by a mere second. Philly will get at least 15 hours a day for the next two weeks.

At 2,255 hours and 55 minutes, summer beats spring for seasonal length by 21 hours and 34 minutes. Taken together, spring and summer are more than five days longer than fall and winter in the Northern Hemisphere. In its annual orbit, Spaceship Earth picks up speed in winter, when it makes its closest approach to the sun and gets a gravitational bump. That’s why February gets short-changed. We are farthest from the sun on July 5. It’s the tilt of the axis, not the distance from the sun, that drives the seasons.

Summer started three weeks ago in the weather community. Meteorologists break down the seasons in three-month increments. It makes bookkeeping easier for agricultural and business interests, and makes sense: Summer weather isn’t confined to astronomical boundaries. (See June 2024, when temperatures have averaged 3.5 degrees above normal.) Similarly, in the Southern Hemisphere, winter got the jump this month in Tierra del Fuego, where temperatures were in the 20s last week, well below normal, says AccuWeather Inc. senior meteorologist Tyler Roys.

A century ago, when almost no one had air-conditioning, the movie theater became the precursor of the “cooling center.” Willis Carrier, among those who share the title “father of air-conditioners,” scored a coup when he persuaded the Rivoli Theater in Times Square to install a system in 1925. It wasn’t the first, but it was a smash hit and gave rise to the heat-busting “summer blockbuster.” That summer movie list includes The Wizard of Oz and Jaws.

Seasonal Affective Disorder is associated with the dark days of fall and winter, but as many as a million Americans endure a summer variant, says Philadelphia therapist Tonya Ladipo. The symptoms include insomnia, hyperactivity, listlessness, and loss of appetite. Sultriness and too much sunlight are among the triggers. To fight it, experts advise getting outside first thing in the morning and taking cool showers. And “make sure you are still engaging with people,” says Ladipo.

The climatologically hottest period of the summer, the so-called Dog Days, unofficially start July 3 and last through Aug. 21 — 20 days before and after the rise of Sirius, “the Dog Star.” The ancient Romans evidently believed that the star added to the Earth’s heat, proving that even the brightest people are clueless about something.

On the early morning of Aug. 28, Mercury, Mars, Jupiter, Uranus, Neptune, and Saturn will align, but neither Franklin Institute astronomer Derrick Pitts nor Haverford College astrophysicist Karen Masters are setting their alarms. Says Pitts, these alignments aren’t that unusual, and we’d be lucky to see one or two of the planets with the naked eye. Masters says she’s more excited about Saturn’s close encounter with the moon on Aug. 20. Of course, August brings us the Perseid meteor showers, those celestial fireflies, peaking the 11th to 13th, but expect some moon interference until late at night.

But you can count on those earthly fireflies, the lightning bug. This is their peak season. While they evoke a certain tranquility, we hesitate to note they have dark sides. Their flashes are all about love, but some devious female bugs have been known to lure would-be mates, only to devour them, according to Lynn Faust in Fireflies, Glow-Worms, and Lightning Bugs.

The strawberry moon rising Thursday is the lowest in the sky of the year. The higher the sun, the lower the moon as the two ride a celestial seesaw. Thus, from here on the moon is in ascendancy, reaching its height near the winter solstice. The next “super moon,” when the moon makes its closest approach of the month, occurs Aug. 19, and while waxing it may dim the Perseids.

The crickets and katydids, the soundtracks of summer nights, will be awakening next month and filling the night air with their mating music. Those are the signals that the exuberance of summer is about to yield to the realities of September and the business of life. As E.B. White wrote, “The crickets felt it was their duty to warn everybody that summertime cannot last forever.”