It is the 50th anniversary of Earth Day. There's a picture of the first Earth Day, 1970 in New York City, and lots of young people are wearing masks. We would have a similar picture today, but would be six feet apart and likely a few years older. For Earth Day this year, our reduced impact due to COVID-19 is being shown with pictures showing the reduction of pollution, showing wild animals walking down main streets, and the song of spring birds being noticeably louder. There are many things about this Earth Day that will become historical.
Earth Day made me think about the scale of things and as I looked at a large bank of clouds was on the eastern horizon this morning, they seemed to look like a mountain range.
Did you know that mountains cast shadows into the sky? Mt. Rainier in Washington State casts a triangular shadow into the sky in a picture from the top of the mountain HERE. Triangular shadows are not seen from objects much smaller than mountains because their shadows are not long enough.
Perhaps as part of Earth Day, we should look at the Earth's shadow. The Earth casts a shadow which is viewable after sunset. Here's the explanation: "After sunset look eastwards. A low horizon is needed but not a volcano. As twilight deepens a dark band rises upwards from the horizon, The band is the shadow of the Earth on the atmosphere. Immediately above, where the evening air is still lit, glows a pink band called the anti-twilight arch or "Belt of Venus". The pink arises from scattered and deeply reddened sunlight mingling with the deep blues of the eastern sky. Look westwards before sunrise to watch the shadow sinking towards the horizon. The shadow is a three dimensional void of unlit atmosphere. The sky high above the shadowed air is bright because it is still sunlit and the air scatters light down to the eye. "
And what about the picture of Apollo 17 astronaut Eugene Cernan's photograph of his own shadow cast on the coal black lunar surface December 1972?
"His shadow, or more accurately his camera's, appears to be surrounded by a bright glow. Cernan's shadow, like many images on the Moon's surface, is surrounded by a bright aureole. It is an example of the "Opposition Effect".
"Lunar soil has an open structure with many areas of deep shadow. But, when looking in a direction directly away from the sun, shadows are hidden by the object casting them. The antisolar point and the adjacent areas therefore appear brighter than elsewhere because they have more sunlit surfaces and less shadow. There are other factors that contribute to the glow, retroreflection by crystalline minerals and a phenomenon called coherent backscattering. The heiligenschein, also at the antisolar point, is a separate effect."
There are no representations of the earth in my database, but there is a picture of Mount Rainier posted last September when we visited Sacramento. The second is a piece of plastic with drew drops at a gas station.
No comments:
Post a Comment