Wed, 02/21/2018 - 14:50
Hello! I am in the process of automating a small box observatory for my Meade LX200 in order to protect it from the elements - rain and wind.
At a pre-determined wind speed, because the CCD images will be poor, the observatory will close. As I use the setup, I'll be able to determine what is appropriate for my system.
For inital wind speed to start with, do folks have a suggestion for speed above which CCD images become poor, and the FWHM becomes too large to be useful? The telescope itself will be protected from the wind and resultant mount vibrations.
Thank you and best regards.
Mike
Of course we all know that seeing, and thus image degradation, is determined by time varying changes in conditions over the entire column from the telescope to the top of the atmosphere, and that moreover surface wind conditions are generally uncorrelated with conditions aloft. So, any number you pick is bound to be wrong, if your expectation is to have good seeing if the surface wind speed is less than X and bad seeing otherwise. In fact, I have experienced situations where the surface winds were quite high, but seeing was good anyway. Rarely, I admit.
For a good introduction to atmospheric turbulence effects on image quality, I recommend you read
Michael C. Roggemann, Byron M. Welsh, and Robert Q. Fugate, Improving the resolution of ground-based telescopes, Rev. Mod. Phys. 69, 437 – Published 1 April 1997
Thank you.
I've observed at Kitt Peak in 60+ mph winds (with the dome slit pointing downwind!) and gotten good results. I've also observed at USNO-Flagstaff when it was calm on the ground, but with the jet stream passing overhead, and had 10+ arcsec seeing. Whether there is correlation between seeing and wind speed depends on your unique situation. A wind screen may or may not be effective, since the blocked wind has to go somewhere. I think the first and foremost issue is safety - make sure you can still close your enclosure, and that the telescope is protected. Then, I'd experiment and see for yourself where the tipping point is between observing and closing.
At USNO-Flagstaff, I typically would observe up to about 25mph with the 1m telescope inside of its dome. I usually selected targets that were downwind when I was near this limit; something you can do when you are at the telescope and not observing remotely. Blowing dust and pine needles inside the dome were also a consideration, in an attempt to keep the optics clean. You mention rain - there was usually a correlation at Flagstaff between wind speed and an approaching front. Sometimes the rain would blow ahead of the clouds, so a cloud sensor wasn't a perfect solution!
Best of luck with your automation...it makes a huge difference in observing efficiency.
Arne