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5

A solid piece of metal with the thickness of 5 layers of foil is just like 5 layers of foil except that, since it is a single solid piece, the "layers" are able to conduct heat (quite quickly!) directly from one to the next. If the layers are instead separated by vacuum, the conduction of heat is eliminated, and heat transfer is greatly reduced (radiative ...


1

Picture yourself looking into a large mirror on the wall. Now picture the mirror is made up of smaller, tiled mirrors. You will still see your reflection. If you begin to remove the tiles, so that there are only a few left, you can still use them to reconstruct the image of your face that was given by the original mirror. This is what is happening with ...


1

Greatly rewritten based on feedback in comments In order to understand this issue, it is worth considering what a telescope (or any optical / radio imaging system) really does. Taking a simple parabolic mirror, the shape is chosen such that the total path length for all rays "from infinity" to the focal point is the same. By making the path lengths the ...


6

The typical extinction for a line of sight out of our Galaxy (but avoiding the Galactic plane) is of order a few tenths of a magnitude at visible wavelengths (it is a factor of 10 less in the infrared and factors of a few more in the UV). This means that the typical attenutation of a signal arriving at the HST from outside the Galaxy is around say ...


52

I've made this into an answer because it's too long for a comment, and I really want to show the pictures. It is tempting to think of visible light as "close enough" to (near by wavelengths) and to conclude that "yes, actually, the yellow does affect it. I want a mirror without an obvious tint" However you are wrong, Physics will slap you down. Exhibit A ...


46

If you look at the reflectivity of gold (vs silver or aluminum) you can see a plateau at wavelengths below 500 nm source: If blue wavelengths are not reflected as well as other colors, the resulting image will look "more yellow" - which is what you see. At longer wavelengths, gold is a very good reflector (better than the other two above 600 nm). It also ...



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