Round Earth Shadow

My practical astronomy has always been pretty awful. I'm a thorough townie - so I quite simply can't see anything in the night sky. A few specks up above and a sodium orange halo around the edges - that's what the sky is to me. But tonight there is a lunar eclipse, happening right now in fact, so naturally I am to be found outside staring at the sky.

As the weather people predicted, it is a beautifully clear night. You can see a lot more stars than you usually can around here - even the plough. And the moon, of course, is being swallowed up by a dark red shadow. A curved shadow - take that flat earthers!

Info here and here (last link via Phil Plait).


zhoen said...

Heavy overcast here. Blast.

Pacian said...

That's usually the way it is around here whenever something happens in the sky. I got very lucky.

Terri /Tinker said...

Lucky you, getting to see the eclipse! Ah well, come August I should get to see the next one (I hope - please don't tell me it won't be visible from this side of the world!) Well, ok, if it won't be please tell me, but break it to me gently :)

Pacian said...

Tinker, take a look here.

You'll be able to see all of it if you're on the west edge of the US, or you'll be able to catch the beginning if you're to the east.

Udge said...

Actually, y'know, the eclipse doesn't prove the earth to be spherical. The earth could be a circular flat plane, and the shadow on the moon would look the same.

I was very lucky, it came at a break in thick overcast, and also just at the point where the moon crossed the alleyway that I see from my kitchen balcony, between my building's roof and the neighbours' roof. It was quite beautiful to watch.

Pacian said...

The earth could be a circular flat plane, and the shadow on the moon would look the same.

Not so:

"Aristotle also believed in a round Earth. He came to this conclusion because of observations of the Earth's shadow upon the moon during lunar eclipses. The shadow of the Earth is always round. If the earth were flat, even if it was circular and flat, the shadow of the earth would sometimes be elongated, like an ellipse. This has to do with the orientation of the Earth. In the figures below, you see a circle. If that same circle is turned about the axis shown, it becomes elongated. Its shadow would have a similar shape. Since the Earth's shadow is always round, the Earth must be a sphere." [Link]

Udge said...

Well, yes but. One might argue back that this is an example of the danger of small samples. Neither Aristotle nor myself has seen all eclipses, perhaps there are many with elliptical shadows that nobody has seen (clouds, mass hysteria, ...) or didn't think to remark upon. Perhaps God is chuckling to himself about how cleverly he's deluded us by always arranging for the flat earth to be perpendicular to the moon at times of eclipse.

Yes, I know: clutching at straws.

Pacian said...

Neither Aristotle nor myself has seen all eclipses

But the world's astronomers have seen (and photographed) probably every eclipse from the past hundred years (if not more). Lunar eclipses are not like solar ones, of course, being visible for everyone on the right side of the world.

And, if lunar eclipses that might reveal the Earth's flat nature were never seen, then we would only ever see those that occurred when the moon was directly over the centre of the disc - and yet, while watching an eclipse we see the moon move through the sky.

So if the Earth was a flat disc we would expect to see the shadow elongate (or become more circular) as we watched the eclipse progress.

Furthermore, different lunar eclipses viewed from the same location will start at different points in the sky. Sometimes overhead, sometimes near the horizon.

Finally, if the Earth was a flat disc, then we wouldn't expect heliocentric, round-Earth models (which do not take into account the fact that eclipses must always be viewed in a way favourable to the flat Earth's shadow) to be able to predict lunar eclipses with the incredible accuracy that they do.

Yes, I know: clutching at straws.

Well, getting at an important point, I think. Perhaps we really are being deceived by a higher being, or perhaps this is all a virtual reality simulation with locations stored in 2D (ie. flat) arrays, or anything else like that. We don't know that these things are not the case. So, knowledge is a matter of certainty, rather than absolute right and wrong.

In this case, though, we are as certain that the Earth is round as about pretty much anything else.