[theoh]

Consider the size of the sun: it's not a point source. Even if it was, the "seeing" (astronomical term for sharpness of objects in the sky) is usually on the order of arcseconds at night, probably much more (due to convection) during the day. So even with image-forming optics, 1 sec temporal resolution is very tricky. (earth turns 15 arcseconds in one second)

[chongli]

Yeah, not to mention the simple problem of diffraction you get when light encounters obstacles such as narrow slits.

[jessriedel]

You'll only get diffraction when the slits are comparable to the wavelength of the light, i.e., on the order of a micron. I believe you can see light peeking out through a micron slit if you're looking directly at it in a dark room, but I don't think it's feasible to see diffraction in shadows. The fuzziness you see in normal shadows comes from the finite angular size of the light source, not the wave nature of light.