November 25, 2006

The Mt Wilson 100 inch primary stripped of its reflective coating. Poured in sections, bubbles of air were trapped in swirls and waves, many very close to the polished surface. Edwin Hubble used this telescope to show that our galaxy was not the whole universe.
  • I can't get over that it's just plain old green plate glass.
  • File that under Aw, Crap! To think of how many other things we could have known about had it been clearer. Wow.
  • Am I wrong in thinking that it wouldn't matter how clear (of bubbles) the mirror was? It's really only the surface that's most important in a dark, dark tube, no?
  • Yeah. This isn't a lens, it's a mirror. They stripped the coating off it so that they could apply a new one. Lemme see if I can find a photo somewhere.....
  • Here we go. This isn't the Mt Wilson mirror, it's the Hubble but it gives you the idea.
  • Neat! This covers the re-aluminization of the 200 inch primary from the Hale telescope at Palomar.
  • Ooooh - OK, gotta stop this cool, so so cool. This is one of the primaries from the Very Large Telescope. 8 metres. 315 inches.
  • Bubbles would not really even be a huge problem even if they were on the surface. You aluminize (or use a better coating) the mirror and then just blacken any bubble "craters". No light is reflected from the defect and the overall loss of light is minimal. The biggest problem to a plate glass mirror is that it changes shape as it warms and cools which can lead to distortion until it reaches the ambient (generally cooler nighttime) temperature. Not sure why they are even going to all this trouble. I would imagine that with the light pollution that has infringed upon Mt. Wilson over the years that any serious work is nearly out of the question.
  • It wasn't until 20 years later that the first aluminum coating was applied. Until then the telescope in its Keplerian mode revealed many secrets of the cosmos, including the Green Spot of Saturn, the Green Rings of Saturn, and the Green planetoids around Uranus.
  • A 100 inch hooker? I have a 12 inch pianist.
  • Mecurious - the observatory has a FAQ The whole thing is worth a read but to answer your question (partly) "Most research programs that study stars are affected very little by ambient light. Light pollution puts a limit on the faintest stars that can be observed but many projects don't need to observe very faint stars. The H-K project -- a 50-year program begun at Mount Wilson in the early 1970's to study activity cycles on the surface of other stars similar to our Sun -- is virtually unaffected by the increase in light pollution in the last 30 years. And projects that study the infrared radiation from stars are virtually unaffected by the glow of the city lights. The city lights that appear so bright to us actually emit very little infrared radiation so the sky still appears quite dark as seen by the infrared "eye" of a telescope. Solar research also continues to play a large role in the observatory's activities, a daytime pursuit that is not affected at all by the nighttime city lights. The programs that are most affected by the brightness of the sky are those that study extremely distant, diffuse objects such as galaxies and nebulae. These projects are generally carried out at isolated, dark observing sites during the dark phases of the Moon. Some deep-sky projects have been conducted at Mount Wilson in the past -- most notably the work of Edwin Hubble and Milton Humason on the expansion of the Universe . But this type of research has never been the primary thrust of the observatory's efforts, nor was it intended to be. While it would be nice for the lights of the cities to stop shining into the sky (thus saving energy and money for Southern Californians), the work at Mount Wilson Observatory continues despite the limitations imposed on some types of research. And when the "marine layer" rolls in -- a low-lying layer of thick clouds from the ocean that covers the Los Angeles area -- the sky can get quite a bit darker. This weather phenomenon isn't predictable enough to include in observing plans so deep sky projects still go elsewhere, but it's nice for the mountain staff to occasionally elude the lights of the cities below and see the sky in all its glory."
  • Ooooooooooo, I like the shiny. A successful coating deposits just a few grams of aluminum across the 200-inch disk making a layer only 3 millionths of an inch thick. Simply 'mazing. Thanks for the info, Poly. *staggers off to read the FAQ and other links
  • Very interesting, polychrome! Thanks fer all the links.