Solar Eclipse: - A Different Viewpoint
13/3/2016
Satellite still, Earth moving
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On the 9th of March there was a total solar eclipse event which was visible from South-East Asia and Eastwards across the Northern Pacific Ocean.
On 12/03 I noted an image posted at NASA's Astronomy Picture of the Day site; "Lunar Shadow Transit", and when following some of the associated links on the page, found this animation. I have seen pictures of the Moon's shadow on the face of the Earth before, but this gif brought home to me something obvious I had not thought of before, that the earth is also turning as the shadow passes across its face. For one thing it gave me new respect for those astronomers who have done the calculations required to produce the predictions we have of the path of future eclipses. Click here for NASA's World Atlas of Solar Eclipse Paths, which, amazingly, can show you the where and when of eclipses from the years 2000BCE to 3000CE! These guys have done the Maths! |
Satellite moving, Earth still
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Another view at Left is a video created by stitching together images captured by the Himawari geostationary satellites operated by Japan's meteorological agency. (Note: IDK why it plays funny, click Watch on YouTube to see.) Note that the term "geostationary" is critical. Because the satellites are (deliberately) orbiting at the same speed the Earth rotates, although we see the Moon's shadow passing, to the satellite the Earth appears still, and it is thus not apparent that the earth is also turning as the shadow passes across its face. |
It is a strange coincidence that although the Sun’s diameter is about 400 times larger than that of the Moon, the Sun is also about 400 times further away. So the Sun and Moon appear nearly the same size as seen from Earth. That’s why we on Earth can sometimes see a total eclipse of the Sun. Article on this coincidence here
The Moon passes between the Earth and the Sun every month, but because the Moon's orbit is tilted with respect to the plane of Earth's orbit around the Sun, it doesn't often line up well enough for its shadow to fall on the face of the Earth. At Left is an image from the APOD site posted 07/08/15, also captured by the DSCOVR satellite, which shows the (to us) far side of the Moon in full sunlight ("There is no dark side...."), without a shadow on the Earth. (The dark edge of the Moon in this picture is the part of the Moon not lit by the Sun, which the satellite can only see the edge of. It is not a shadow on the surface of the Earth.) |
For those wishing to consider all the angles of the subject, refer below.
Postscript: Pretty, But Fake!
Apparently this picture went viral at the time. It came up in my searches and I considered using it, but it looked so good I wondered why I hadn't had it appear before me before now. I looked for the source, and found out it is an artwork, copied, mis-labelled, and spread about by the credulous and ignorant. Ref. debunking here at the website Gizmodo. |