Explaining the summer solstice as the sun hits its high point over Philly

The meteorologists once again are calling for higher-than-average temperatures through August (so what’s new), and an overactive tropical-storm season (ditto).

On the bright side, the moon is getting ready to pick up its game, and we have at least an outside shot at catching the northern lights sometime in the next few months.

Welcome to the longest season of the year, when the air is at its steamiest — and noisiest. And here’s why the heat might make you crabby.

» READ MORE: Expect another hotter-than-normal summer. At least that's the forecast.

The big moment occurred before sunrise at 5:14 a.m. Tuesday, when the sun’s direct light reached its northernmost point of the year, beaming directly over the Tropic of Cancer.

“Tropic” is derived from the Latin and Greek roots that suggests a turning, and this is an astronomical turning point in the solar year. The sun’s most-direct light has begun a six-month, roughly 3,200-mile migration southward to the Tropic of Capricorn, its southernmost point, at the winter solstice.

“Cancer” is Latin for crab. When this thing was identified and named over 2,000 years ago by an unknown but very keen observer, the sun was aligned with the constellation Cancer this time of year, points out Harry J. Augensen, a Widener University emeritus professor of physics and astronomy. Well, heat actually can induce a certain crabbiness.

It’s almost a dead heat, but at 2,255 hours and 55 minutes, summer bests spring for duration by just 21 hours and 34 minutes. Combined, astronomical spring and summer are more than five days longer than fall and winter in the Northern Hemisphere. That’s because the earth speeds up in winter as it makes its closest approach to the sun and the calendar sheds a few days. Ironically, the earth is farthest from the sun around July 4. The seasons are all about tilt (see below).

» READ MORE: Leap year, and what we lose in winter

The sun’s wattage over Philly peaks on Tuesday. But on average, the date with the highest daily temperature, based on 148 years of record in Philly, is July 17, at 87.4 degrees. It takes awhile for the solar hot plate to cook the air. Plus we have something called the Atlantic Ocean nearby with surfaces waters that are still quite cool and can have a chilling effect when winds blow from the east.

With 15 hours, three minutes, and 47 seconds between sunrise and sunset in Philly, June 21 is in a virtual tie with June 20 for most daylight hours. From here the days do get shorter, but chances are you’ll hardly notice for a while. The sun actually will be setting ever so subtly later from June 22 to July 4. The daylight leakage proceeds glacially, and doesn’t slip below 15 hours until July 2.

The full moon, which has a seesaw relationship with the sun, will be beaming progressively higher and longer. It will celebrate this ascendancy with a supermoon rising on July 13, a mere 222,000 miles or so from Philadelphia, its closest approach of the year. It will be in the sky 17 minutes longer than the June full moon, and August’s full moon will be up there about 90 minutes longer than June’s.

It’s always a long shot, but the surface of the sun is getting stormier, says space scientist Rob Steenburgh, acting lead of Space Weather Forecast Office. That increases the odds that it will eject those magnetic particles that make northern lights possible.

While sun storms potent enough to generate a night-light show at our latitude are “less common” than the weaker ones, said Steenburgh, they have been known to happen.

Rain forms when warm air rises over cold air and condenses, and with the heated ground energizing the atmosphere, summer is far and away for thunderstorms in Philly. On average thunderstorms occur on about 16 days throughout June, July, and August, about 60% of the annual total.

» READ MORE: This is a prime time for thunderstorms

It’s the first day of winter in the Southern Hemisphere, where, outside of Antarctica, it’s not nearly as wintry as it is up here. A big reason is that the Northern Hemisphere has way more land mass upon which snow can fall. Also, oceans do a great job of retaining heat.

The tilt of earth’s axis is the key driver of the seasons. Currently the tilt is about 23.5 degrees, but over millennia, it varies between 22.1 and 24.5. The greater the tilt, the more heat in summer, the more cold in winter. The tilt is heading back to that gentler 22.1, when the seasons theoretically would be more benign (climate change notwithstanding). You’ll have be patient, however. This will take about 10,000 years, and when it happens, no doubt computer models will still be squabbling about what it means.

Our solar system offers generous alternatives in lengths of summers. They range from seven months on Mars to three years on Jupiter to more than 40 on Neptune. Summers can be rather chilly on Neptune, since it gets only about a thousandth of our sunlight and the is about 392 degrees below zero, Fahrenheit.

Windchill factors were unavailable.