thanks!

I think you need to do a blog entry on the last one though, explaining the reason the stars can be seen. There is a similar picture of the aurora circulating the web that has starts visible in it (I think it was on APOD one day), and I saw a moon hoaxer website using it as an example where we should be able to see stars blah blah…

From memory it was just due to longer exposure time, and you could tell because the clouds were fuzzy.

See crop cirlces are real….
what??

circular crops?? never mind

Although you are right, the earth gravitational influence on things is strong enough that it causes a measurable effect of “time delay” on satallites. In fact, the GPS satallites must all correct for effects of SR and GR in order to give a correct position!
Without GR GPS would lead you anywhere but not where you want to

Nit: the moonlight gets bent downward as it enters Earth’s atmosphere, not upward. If it were truly upward, the moon would appear stretched, not squashed.

Double-nit: if one views the pic from a land-dweller’s perspective (head tilted to the left), the Great Grey Egg does “appear” stretched.

Does a double-nit cancel out a single-nit?

Yes, indeed! But the effect around the earth is FAR (and I mean VERY far) to weak to account for something detectable. You really need a strong gravitational field to have such a “lensing” effect – a field close to a black hole.

Thanks, DrFlimmer and zandperl. When I wrote my entry, I was actually thinking along those lines, too; and also that Earth’s gravitational force is too weak to cause significant time dilations.

That’s no moon! It’s a Space Station!

Thank you, thank you. It had to be said.

Thanks BA, I scrolled down through all of those & my favourite of them all was the very last one (35) showing the aurora australis and the stars and the Earth’s limb and atmosphere. Awesome. Truly. Awesome.

@ 7 TS :
Them wacky Australians turn everything upside down, including astronomy pictures.

Actually no you’re the ones who are “upside down” and we’ve got everything the right way round!

There is no up or down in space! North & South are arbitrary as is the convention that “north is up” not vice versa.

(*Waiting eagerly for the next terrestrial magnetic field reversal.*)

So do these things.

http://www.rathergood.com/moon_song

@lawyerchik1: moon crashing into earth seems to be a popular story – but it’s not going to happen (despite the slow degeneration of the moon’s orbit). I think the BA discussed that issue in Bad Astronomy – I’m sure you’ll enjoy reading the book. Of course a very large comet can always come along and encourage the moon to make a landing. It’s got to be quite a comet though to be able to impart enough energy to reduce the moon’s motion enough that it falls to earth.

Can you now stand the moon on end at the equinoxes?

BTW, I would object to the description “a thick shell of air.” Relative to the size of the body it surrounds, the Earth’s atmosphere is far thinner than the skin of an apple.

- Jack

No — the effect is much too small to contribute to the ‘flattening’ of the Moon’s image shown in this photo.

If you want a GREAT cross-country ski experience, (or nice hike / mountain bike), the valley to the north runs on the south side of Mt. Rundle… from Canmore to Banff. It’s amazing. It’s also amazing to see such a beautiful part of the world from on high.

Your explanation doesn’t seem quite right to me though: The light with the steeper angle, ie the bottom ray, will be bent LESS than the top one; a ray at 90 deg to the surface would not be bent at all. I think what you might have done is forgotten that the values in Snells law are the angles from normal, rather than relative to the surface.

If we consider a ray that just grazes the top of the atmosphere, then the angle (from normal) will be ~90 deg, giving the maximum refraction. However the refractive index at this point will be very low and so there will not be much deviation.

If we treat the atmosphere as many concentric shells of increasing density, then the lower ray will pass through more shells of higher refractive index resulting in greater deviation and explaining the observed distortion. The resulting greater number of transitions, and their larger refractive index is the key to understanding the picture. Of course one has to make the number of shells tend to infinity to get the full answer, but I think this establishes the principle.

Nit on nit: Unless I’m mistaken, by that reasoning nothing would happen but a roughly parallel translation typical of light passing a window at an angle. The upwards refraction when entering the optically denser material (so refraction angle less than incidence angle) is roughly counteracted by the downwards refraction when leaving it (so refraction angle greater than incidence angle). It’s the curvature (and graded index) that makes the difference between paths.

I agree with #16. Light from the bottom of the moon bends a bit more around the Earth so when the light from the top and bottom converge at the ISS, the angle is smaller.