Very fascinating Louis. What a great job you have. What is the angular size of the false star that the laser creates? Also, I always thought that the corrections for atmospheric distortions were done by adjusting the primary mirror, but the other day someone told me that it is actually done with a small focusing screen in front of the camera. It that true?
Sorry for the technical "non-observing" question, but it is great to have an expert on this subject here on the list--so I couldn't resist asking.
Bill Drelling
Louis Hlousek <louandchop@No-Spam> wrote:
We don't yet have the laser so haven't been propagating the beam on the sky down here. In the North they have a 10W laser single guide star system which is in use but I haven't seen it in operation yet. It's projected on the sky via a 44cm telescope that is behind the 1m secondary, so the beam is 44cm in diameter. Incidently, 44cm is about the same size as the Discovery DOB I have on order. Anyway, I hear it can be seen when you're up to several hundred meters from the scope. The laser guide star is created by the fluorescence induced in a layer of sodium atoms that resides about 90 km up. The layer comes from evaporated micrometeors.
Keck has a laser AO system on one of their scopes but use a refracting telescope mounted on the edge the top ring to launch the beam. They went in with Gemini on procurement of lasers and are getting a 20W version for their other scope which will launch from behind the secondary.
One of my jobs is to get the laser beam from the laser, which is roughly as big as a telephone booth and rotates with the scope in azimuth but not elevation, to the laser launch telescope behind the mirror. There are quite a few nuances involved regarding structure flex, polarization, beam rotation, generation of 5 beams from one, etc.. I'm going up to the scope next week to help with collimating the laser launch telescope on a natural star. Get this; as the big scope is aimed and guiding on a star, a guy goes up 20 meters on a scissor lift to the secondary cage and reaches in to tweek the laser launch telescope collimation while somebody else watches the star's image on a monitor and relays instruction to him via walkie talkie.
As far NZ darkness, I was touring the south island via on/off road motorcycle so was in the back country much of the time. That was way back in the early 90's.
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Received on Sun Jan 20 08:11:06 2008