Current News

/

ArcaMax

What to know about the autumnal equinox as the days shorten before our eyes

Anthony R. Wood, The Philadelphia Inquirer on

Published in News & Features

Visually, not much; you won’t feel a thing; and your shadow will look like it does on other days at 3:20 p.m. Astronomically, however, this is mega-event foreshadowing significant changes in the weather.

At the instant of the equinox — and it’s only an instant — the sun will beam directly above the celestial equator, that imaginary line that divides the planet in two. At the summer solstice, direct light was about 1,500 miles to the north, on the Tropic of Cancer, thus the longer days and the stronger sun up our way. Winter will begin when it’s over the Tropic of Capricorn, 1,500 miles to the south.

At the equinox — derived from the Latin for “equal night” — day and night aren’t precisely equal, but it’s close. At Philadelphia’s latitude the closest the area gets to even split is Sept. 26, when the day will be a minute and 16 seconds longer than the night. From then until the winter solstice, nights will increase their advantage.

The planets, in 3D

While pondering the skies, you can see Jupiter and Venus every evening these days, along with Saturn. Venus is apparent in the southwest sky, and the sun is politely getting out of the way earlier and earlier.

To the southeast “creamy colored” Jupiter is dominating, with Saturn in the background, and they are coming ever closer together, says Derrick Pitts, astronomer at the Franklin Institute.

 

He points out that Saturn is about 885 million miles from Earth, and Jupiter, 484 million.

“The gulf between them is almost the same as the distance from earth to Jupiter,” Pitts said. “People now get a more three-dimensional view of the solar system. It’s no longer dots on a velvet curtain.”

Jupiter and Saturn are roughly the same size, yet Saturn appears so much smaller, attesting to the distance.

Coming through — the birds

...continued

swipe to next page
©2021 The Philadelphia Inquirer. Visit inquirer.com. Distributed by Tribune Content Agency, LLC.