Images credit & copyright: Daniel LaShomb.
On any given clear evening, while you’re facing west watching the sunset, take a moment to turn around and admire something I find just as beautiful; Earthshadow and the Belt of Venus or as I call it, “the tide of night rolling in.”
Let’s take a step back and unpack this a bit shall we? As the Sun sets below the horizon in the west it casts a shadow on Earth’s atmosphere and out into space to about 1,500,000 km (932,000 mi.). A shadow of what? The Earth itself! That’s correct; as the Sun breaks below the horizon, the shadow of our very planet can be seen cast across the opposite horizon (that’s the blue/purple part). Think of angles; as the Sun sets further, Earthshadow grows wider until it becomes the night itself. After all, that’s what night is; existence in Earth’s shadow. If you have an especially wide open horizon such as the beach, you can actually see the curvature of the Earth in its shadow. It’s visibly thin at one end, reaches its widest point at the center and tapers off again on the other side.
The second part of this beautiful duo is the Belt of Venus and it’s the pinkish colored band that sits atop Earth’s shadow. It’s an antitwilight arch caused by sunset light being backscattered to the opposite horizon. As the Sun reaches the horizon it’s at its reddest and that light is illuminated in particles which encircles the entire horizon.
As I’m a night sky guy I’m biased but to be fair, just as Earthshadow and the Belt of Venus appear in the east as the Sun sets in the west, it also occurs in the west during sunrise in the east. The only difference is that when it appears in the evening Earthshadow gets wider as it brings night with it and when it appears in the morning it recedes as its being chased off by the Sun. Give it a look and see our planet’s shadow twice every day and if you want an extra treat; have a look the day before a full moon and watch the nearly full moon rise atop or within this beautiful phenomenon.