Normally we do not open the shutters during the day. As any kid who has used a magnifying glass in the sun knows, direct sunlight and optics are a powerful combination. The amount of sunlight a 10 meter mirror could gather would result in something a bit more powerful than a child’s toy.
Occasionally it is necessary to do maintenance on the shutters, in the process opening the shutters during the day. It is a careful operation, turning the dome away from the Sun and positioning the telescope away from the opening. Still, it is an odd situation, daylight streaming into the dome, a place normally only lit by starlight or the dome florescents. Then there is the view…
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I never thought about the fact that there is no cover over the mirror! At the Palomar Hale 200-inch a cover closes over the mirror at the end of the night. It closes kind of like flower petals. Anyway, nice photo, and nice view! – Maureen