If you ever marveled at how much dust accumulates on the surfaces in your home in just a few days, you can probably appreciate how much effort it takes to keep the mirrors clean inside the dome of an observatory. The Rubin Observatory Auxiliary Telescope (AuxTel) has been taking observations of the night sky since early 2020, and every week the AuxTel team sets aside time during the day to clean the three mirrors inside the telescope. The actual spraying of the mirrors only takes a few minutes, but moving the telescope, measuring the reflectance and scattering of the primary mirror after cleaning, and checking that all systems are back online afterwards adds up to about 30 minutes of effort.
The attached video shows technician Claudio Araya spraying the primary mirror with CO2 "snow." This is a common method for cleaning large telescope mirrors—the CO2 pushes the dust off and then evaporates without leaving any residue. Claudio is an expert in this very specific task; he has more than 15 years of experience cleaning telescope mirrors, first for Gemini Observatory and now for Rubin Observatory. In addition to the weekly CO2 spraying, the AuxTel mirrors also undergo a "semi-dry" wash about every 3-4 months, in which they are dabbed with natural sponges that have been soaked in distilled water and then wrung almost dry.
The routine for keeping the AuxTel mirrors clean is usually pretty uneventful, but not always. One day the team discovered a small bird had gotten into the AuxTel observatory (which was unexpected, since the dome is typically closed during the day when birds are active), and the bird had perched above the telescope. We probably don't have to tell you what the team's concern was, but they immediately opened the dome and encouraged the bird to fly away. Once that happened, the team checked the primary mirror surface carefully--fortunately it had been covered during the bird's visit and no gifts were left behind.
The mirrors on Rubin Observatory's main telescope will also need to be cleaned periodically; the details of exactly how that will be done, and how often, are still being developed. We look forward to sharing videos of that process in the future!
Financial support for Rubin Observatory comes from the National Science Foundation (NSF) through Cooperative Agreement No. 1258333, the Department of Energy (DOE) Office of Science under Contract No. DE-AC02-76SF00515, and private funding raised by the LSST Corporation. The NSF-funded Rubin Observatory Project Office for construction was established as an operating center under management of the Association of Universities for Research in Astronomy (AURA). The DOE-funded effort to build the Rubin Observatory LSST Camera (LSSTCam) is managed by the SLAC National Accelerator Laboratory (SLAC).
The National Science Foundation (NSF) is an independent federal agency created by Congress in 1950 to promote the progress of science. NSF supports basic research and people to create knowledge that transforms the future.
NSF and DOE will continue to support Rubin Observatory in its Operations phase. They will also provide support for scientific research with LSST data.
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