Sunday, August 27, 2017

soft shadows

I thought about the "fast-moving shadow across the landscape or clouds" during a total solar eclipse.

Many people talk about this feature of a total solar eclipse and say that it is something to watch for. It should occur moments before 2nd contact and moments after 3rd contact. At Glendo, many were facing west just before totality to try to observe it.

I myself did not notice anything or see what I expected. And as I watched videos and played them back over and over, I felt unimpressed.

Ian and I talked about it on the drive back.

And I think I figured out the issue.

I was expecting a sharp, obvious, delineated shadow like one sees under clouds. In fact, on Saturday before the eclipse as we drove through Nebraska and Wyoming, I watched the low fluffy clouds cast dark shadows on the ground. I even thought at the time, "This is what I'll see." And that was wrong.

Ian and I considered that one of the factors is distance. Or distance ratios. The sharp shadows under clouds are obvious because the occulting object is very close to the ground and the light source is far away. Low-level clouds are below 2000 metres. But when we consider the Moon over the Earth, it's around 400 000 kilometres or 400 000 000 metres away, on average.

I wondered if another contributing factor was air.

No comments: