Sunsets can be dramatic and colorful. Those are hidden from us behind trees and the mountain. But we have a good view to the east that lets us see not the sun going down, but the dark coming up. It’s the shadow of the Earth.
We spend every night in the shadow of the Earth.
This is the view directly to the east on Sunday evening, just before sunset.
The east is blue, with a hint of pink.
The sun is still up, illuminating everything we can see to the east. But as the sun drops, something else rises.
Sunset starts
There it is. Just a hint, right below the pink, the shadow of the Earth.
A little while later, the Earth’s shadow creeps up into the sky.
The shadow of the Earth rises
Near the horizon, just above the shadow, the sun’s rays are passing through as much of the Earth’s atmosphere as possible, and most of the blue is filtered out. So we see what’s left, the red part of the spectrum.
There’s something about that shadow that’s not quite on the level. Can you see it? Here it is a little later, zoomed a little.
The sky darkens
Can you see the slope? We’re looking almost due east here, and the Earth’s shadow slopes up from south to north. That’s because the sun is setting towards the south, and the near-cylinder of the Earth’s shadow points towards the north, where the sun will rise about a month after the first day of spring summer. That slope is the curvature of the Earth.
Shortly after this, the shadow of the Earth moved up into the sky as the sky darkened everywhere, and it was no longer possible to differentiate the Earth’s shadow from the dark sky.
If you lived on a high mountain with a good view in all directions, you could watch the dividing line between daylight and night, which is called the terminator, as it speeds across the landscape. The terminator moves at a little over 1000 miles per hour at the equator, and at about 850 miles per hour at the latitude of our house (about 35 degree north). That’s fast. Sometimes we can see to Kennesaw Mountain, just outside Atlanta, so let’s say we can see 40 miles on a good day. At the speed of the terminator, it would take less than three minutes to cover the distance from where we are to that point.
But there are too many hills and valleys here to actually see the terminator move across the surface. We’ll have to content ourselves to watch the Earth’s shadow cast on the air itself.
Great pics! I had no idea the curve of the earth could be seen in the shadow at sunset looking east. That is such a wonderful phenomenon of light and shadow. Unfortunately, we don’t have a clear view either east or west, too many hills and mountain between, so I wont be able to see this here. I remember once driving across the prairie in Saskatchewan in the early 70s and looking as far as I could see, and thinking I could actually see the curve of the earth.
Neat photos and explanation! I have probably camped in places where I could have seen the terminator had I known to watch for it.
I originally said that the sun will rise in the east opposite of where it set last Sunday about a month after the first day of spring, but that’s not right. Last Sunday was about a month after the winter solstice, the first day of winter, when the sun rises and sets the furthest south of any day of the year. If you follow a line from the sunset through our house, it points north of due east at about the same place the sun will rise a month after the summer solstice.