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Al Stahler: Sun stands still


It’s against the law to hitch-hike on California freeways, but other states let you stick your thumb out. Thumbed rides do not come free … the driver expects you to pay with conversation.

Watching those cars and trucks go by from the side of the road, you know they’re moving 60, 70 miles an hour – a mile a minute.

Some hours of the day … and many hours of the night … the freeway is pretty much empty. Every now and then, a car approaches. As you look down the road, the car doesn’t seem to approach nearly as fast as it moves when it passes – it moves in slow motion. It’s an angle effect, the car moving toward you at an angle.

My ride drops me off, and, with thanks, I head upward, into the mountains. Reaching the first ridge – the first major border I’ll cross in my escape from civilization – I look down. Now miles away, cars and trucks on the freeway look tiny. And, from this distance, cars and trucks move in slo-mo … not an angle effect, but a distance effect.

The stars we see at night are moving really fast. But the stars are so far away, the scorpion we’ll see tonight is the same scorpion folks first noticed, thousands of years ago. It’s that distance effect again, shifting the stars into slo-mo. Even astronomers – who know darn well those stars are haulin’ – refer to them as fixed stars … not moving, but fixed in place.

Planets circle the sun, close enough to Earth that we can see them move through the sky, week-to-week … sometimes night-to-night.

The moon is way close. Earth spins faster than the moon falls around us, but the moon moves through the sky so fast, from one night to the next, we’ve got to play catch-up. The moon will rise later tonight than it rose the night last, and will rise even later tomorrow.

And then, there’s the sun.

Earth circles the sun at 65,000 miles an hour – a thousand miles a minute. Pretending that we are standing still, we can almost see the sun move through the sky, minute-to-minute. We can, for sure, see the sun move one hour to the next.

It’s our spin that makes the sun move … and its motion is complicated by the fact that we spin, not straight up-and-down, but at a slant. That slant throws an angle effect into the sun’s motion through the sky.

At dawn … between the darkness of night, and the first spark of the rising sun … is twilight. In the evening … between the last glimmer of the setting sun and the pitch black of night … again, there is twilight.

And, because of our slant – as on the freeway – there is an angle-effect.

Last Monday night/Tuesday morning … a couple of hours after midnight … Earth passed through summer solstice. The word “solstice” derives from Latin: “solar stand-still.” It’s that angle-effect again: For just a few days, the sun stops moving through the sky. The angle-effect on twilight is obvious: Twilight – in the weeks before and after solstice – lasts more-or-less forever. At dawn, the eastern sky grows light … but we wait … and wait … and wait … for the sun to finally come up. Come evening, the sun goes down … but it takes more-or-less forever … for the sky to turn black.

This week’s summer solstice marks the longest day of the year … in the north. In the southern hemisphere, it’s winter; Antarctica sees no light at all.

Al Stahler enjoys sharing science and nature with friends and neighbors, in The Union and on KVMR-FM. He teaches classes for both kids and grown-ups, and may be reached at a.a.stahler11@gmail.com

North pole enjoys solstice sunshine, 24/7; south pole sees no sun.
Courtesy Takmeng Wong/CERES SciTeam/NASA LRC

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