@29. Uncle Al : Also, you do realise that any solar flare or storm severe enough to down the International Space Station would also probably take out many of the vital satellites that provide us all with GPS, Global TV broadcasts, weather forecasting, etc .. Right?

In fact, it would take out satellites first. I think the ISS is in a pretty low orbit as these things are reckoned. Geostationary satellies orbit outside the Van Allen belts, so have very little protection from our magnetic field. The ISS orbit is well inside both belts, so has nearly as much protection from charged particles as much of Earth’s surface.

(BTW, I don’t mean that the Van Allen belts themselves protect Earth from the solar wind, but they are the destination to where our magnetic field diverts much of the radiation. Above the Van Allen belts, the magnetic field has yet to achieve much with incoming radiation, and below the belts, much of the radiation has already been trapped or diverted.)

Plus such a cataclysmic solar storm would have effects here on Earth too. I think I recall reading a chapter about that in a certain book about Death Fom the Skies by an author whose name escapes me right now, think it started with ‘P’ and ended in ‘t’ or something!

Yup. Any solar storm or CME of sufficient power to take out the ISS would also take out most of the power-distribution grids on Earth (or, at the very best, put them off-line for a few hours).

What we perceive as the moon being “larger” when it is nearer the horizon is merely an optical illusion called ocular macropsia. It appears bigger only because it is nearer smaller objects we don’t normally compare it to (trees, homes, buildings, hills, mountains, etc.). It is the comparison that makes it appear larger. In reality, its angular size does not change.

When it is higher in the sky, it is next to objects that are on much larger scales (constellations, stars, etc.) which we more frequently compare it to (which is why we perceive the moon in the sky as its “normal”-looking size). This is called ocular micropsia.

This is a very nice explanation, but sadly it is wrong.

If it were right, then we could make the apparent size of the moon vary by standing near to or away from nearby objects, and this does not happen.

If you have a perfectly flat horizon with no trees, buildings or anything like that anywhere in your field of view (say, in the middle of a calm ocean), the moon illusion still happens. It still seems bigger near the horizon that it does near its zenith.

The best explanation I have seen for this is along these lines:
Our brain models the entire world from visual input. What we think we see is actually our brain’s model of our surroundings, with very little accurate detail (except directly where we look). Experiments can be done to show that if part of a scene changes while we are looking at a different part of the scene, we are unlikely to spot the change.

The brain’s model of the sky is a shallow upturned bowl, with the zenith much closer than the parts of the sky near the horizon. If you consider that, on a cloudy day, the visible sky is indeed much closer overhead than near the horizon, you may see that this makes a kind of sense. Thus, the brain’s model tells us that objects in the sky overhead are closer to us than objects near the horizon.

The real angular size of the moon does not change perceptibly from being overhead to being near the horizon. Thus, our brain models it as a large object very far away when it is near the horizon and as a smaller object rather closer when it is overhead. To compensate for the disparity between the actual angular size and the modelled “actual” size of the moon, our brain makes it appear to be larger when it is near the horizon (and thus a large object very far away) than when it is overhead (a smaller object a lot closer to us).

The same effect occurs with the sun, but we almost never look at the sun when it is overhead (well, duh!) so it is noticed far less often.

This effect was mentioned in a recent episode of QI. Stephen Fry showed a speeded-up video of the moon setting and asked the panel to buzz when they thought the moon had actually disappeared below the horizon. Of course they all buzzed when the moon had visibly gone, but then he dropped his bombshell. No, Fry announced, by the time you see the bottom edge of the moon touch the horizon, it has already set! The atmosphere bends the light so you still see the moon above the horizon, by about the same amount as the moon’s apparent diameter.

I saw that episode and it was a sunset, not a moonset. But the principle is identical.

Plus such a cataclysmic solar storm would have effects here on Earth too. I think I recall reading a chapter about that in a certain book about Death Fom the Skies by an author whose name escapes me right now, think it started with ‘P’ and ended in ‘t’ or something!

It’s amazing we haven’t seen that before.

I guess you don’t peruse the Atmospheric Optics website?

http://www.atoptics.co.uk/atoptics/moonflat.htm

A moonrise sequence from an earlier space station, Skylab.

And http://www.atoptics.co.uk/atoptics/issmoon.htm

Moonset from the ISS. On 16th April ’03 Don Pettit, the ISS science officer, imaged the full moon as it set behind the Earth’s limb.

Reminds me of the time I wondered as a teenager why the moon was larger (or so I thought) near the horizon than when it was higher in the sky. A few hours on the internet (pre. google or wikipedia days) and the family encyclopedia (actual physical encyclopedia) yielded the following … What we perceive as the moon being “larger” when it is nearer the horizon is merely an optical illusion called ocular macropsia.

BTW. There’s plenty more about that “Moon illusion” via this blog & the BA here :

http://blogs.discovermagazine.com/badastronomy/2010/05/13/why-does-the-moon-look-so-huge-on-the-horizon/

Plus here :

http://blogs.discovermagazine.com/badastronomy/2007/06/30/big-moon-tonight/

and also :

http://blogs.discovermagazine.com/badastronomy/2010/06/07/very-large-moonset-but-not-why-you-think/

there. If folks wish to read further. (I always do! )