Celebrate Summer’s Start ’round About Midnight Friday

A radiant sun shines through a cluster of Norway pine needles. This Thursday-Friday marks the summer solstice or first day of summer.  The season begins at 1:04 Eastern time June 21 and 10:04 p.m. Pacific  June 20. Credit: Bob King

“Summer afternoon—summer afternoon; to me those have always been the two most beautiful words in the English language.”  – Henry James

So it’s always seemed to me at the start of a summer vacation. Endless time laps ahead like a wave that never breaks. Those splendid hot stillnesses are returning. Come Friday June 21 at 12:04 a.m. CDT summer tiptoes through the dark to quietly unseat spring; the next three months belong to the high sun, iced drinks and late evening light.

Whichever end of Earth’s axis points toward the sun, it’s summer in that hemisphere. In June, the north polar axis tilts that direction and we experience summer (left). When it points away, it’s winter. At the fall and spring equinoxes, the planet is tilted neither toward nor away and day and night are equal. Credit: Tau Olunga

That’s in the northern hemisphere of course. Way down south it’s the first day of winter and the sun is never lower in the sky than on June 21. Here in the north, the sun beams from its highest point in the sky. Since it spends a great deal of time climbing to this lofty perch and an equally long time descending, summer days are exceptionally long. Daylight squeezes night into a narrow slot fewer than 9 hours long.  With darkness beginning after 10 o’clock, skywatchers are forced to choose between sleep and stars.

A mosquito from early Miocene times (~ 20 million years ago) frozen in time in Dominican amber. Credit: Didier Desouens

If the choice is stars, you’ll be sharing it with tiny, whining friends of the night. Mosquitos have been around for millions of years; our most distant human ancestors slapped and batted them away just like you and I do every time we look up in wonderment without protection on a pleasant June evening. But there are fireflies too and owls and frogs about, making a clear summer night as much a sonic experience as a visual feast.

All this summer stuff happens for one reason – the tilt of Earth’s axis. Simple as that. No need to bring in the experts, no special app required. Earth circles the sun tilted 23.5 degrees from vertical. Every June 20 or 21 the northern hemisphere points toward the sun, causing it to appear high in the sky. Not only do the days reach their maximum length, the sun’s high angle means the energy per unit area it pours over Earth’s surface is more than twice as intense as during the winter.

Six months later the north tilts away from the sun. A low sun and less intense surface heating means wintry consequences.

Male fireflies flash as they fly over the ground looking for a mate on a June night. Credit: Bob King

Spring and autumn fall between winter and summer extremes with Earth broadside to the sun and neither axis tilted toward or away. Day and night briefly agree to share the clock equally before charging off to the next season.

So yes, I’m ready for summer. Bring on the sweet smells of morning air, those endless afternoons and nights of fireflies tearing across the sky like biological meteors.

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