posted on Oct, 2 2010 @ 01:03 PM
reply to post by Spartannic
There's more to research than looking at a computer.
Most of what I learned I gleaned from touring observatories - Palomar, Mount Wilson, Kitt
Peak, Stewart, Mount Hopkins & Lowell Observatory.
First, a quick primer on pre-digital photography. I'll describe black-and-white because it is easier and more relevant, since that's what
astronomers use. They would start with a glass plate covered with very fine-grained silver-nitrate crystals, which were sensitive to light. When
exposed to light and then washed with a chemical developer, the exposed grains would turn dark. The more light they were exposed to, the darker the
crystals would turn. Thus, in the resulting image, all the things that were bright show-up as black, while those areas that were not exposed to light
were clear - A negative image.
To make a positive image, they would either project the negative image onto a fresh plate or piece of photographic paper, or place the negative
directly on the fresh surface and shine a light through it (the latter process is called making a "contact print"). The light shines unimpeded
through the clear areas of the negative and exposes the fresh surface. The dark areas of the negative block the light and thus those areas of the
fresh surface do not get exposed. When the fresh plate/paper is developed, it shows a
positive image.
The plates were clean when they were removed from the wrapper and installed at the focal plane of the telescope. After they were exposed, removed and
developed as photographic negatives, they looked like clear glass squares with black specks & smudges - the reversed images of stars & nebulae.
To make positive reproductions, i.e. pictures that show white stars on a black background, they would take the plate out of storage, wipe it off and
loaded it onto a device that projected the negative image onto another photographic plate or peice of photo-sensitive paper. When developed, the
black specks show-up as white stars on the new image. Now then, if there was any dust or lint on the negative, that would block the light from
reaching the fresh surface, leaving a white image of them on the positive reproductions. This is how such artifacts sneak into the official
record.
Hope this helps.