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Wallpaper 4 [Aug. 21st, 2007|05:29 pm]
dalekboy
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[mood |cheerfulcheerful]

Yes, another post featuring some of my favourite wallpapers on the computer, all scaled down so they don't devour your bandwidth.

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Venus passing in front of the sun.


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Lots of galaxies!


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Picture of the surface of Titan. I've no idea why, but this photo thrills me more than shots from places like Mars and the like.
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Comments:
[User Picture]From: talmor
2007-08-21 08:30 am (UTC)
Nice pictures, but I'm afraid that one of the moon's shadow over Europe during a solar eclipse is a fake. The Sun isn't a point source, it's about half a degree wide. That means shadows from sunlight have 'fuzzy' edges, above and beyond any diffraction effects. If you look at the shadow of a telephone pole, it's sharp at the bottom, and fuzzy at the top, where the 0.5 degree angle has more distance to spread out.

If the moon is casting the shadow, 385,000km away, that half-degree between full light and no light is almost 3400km on the Earth's surface, assuming the Sun went behind a straight edge. The fact that the Moon is round means it's even 'fuzzier' on the edges of the shadow (called the penumbra, the area where any part of the face of the sun is blocked off). The only shadow edge you can see from space is the 'Umbra', in a total solar eclipse, which is the area where ALL of the face of the sun is blocked off. That's much smaller, tens or hundreds of kilometers across, not thousands. Even that's a bit 'fuzzy edged' because of difraction.

There's a good image of a real eclipse shadow here:

http://earthobservatory.nasa.gov/Newsroom/NewImages/images.php3?img_id=17228
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[User Picture]From: dalekboy
2007-08-21 09:17 am (UTC)
Knew it was a fake, but still like it.

Like the shot from the real eclipse - it's like a huge dead spot on the planet.
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[User Picture]From: redbraids
2007-08-21 01:01 pm (UTC)
Now you will be telling me that the Easter Bunny is not real! :-) :-)
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[User Picture]From: rendragon
2007-08-22 11:12 pm (UTC)
My husband has a really neat background on his laptop (unfortunately a mac) which shows a map of the world with the day/night cycle moving across it - it's current and updates so you can watch night creep across a continent and the world turn from day to night, etc.
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