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Moon through a professional telescope | by Juan-Carlos Munoz-Mateos
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Moon through a professional telescope

What do you do when you have an empty focus in a professional telescope? You put a screen and project the Moon on it! That’s what we did last night at the UT3 telescope, here at Paranal Observatory.


UT3, like the other UT telescopes, has several foci: two at the sides, called Nasmyth foci, one underneath, called Cassegrain focus, and one under the dome, called Coudé focus. At each focus there’s a different scientific instrument. A movable mirror in the center redirects the incoming light towards whichever focus we want. We can switch focus in less than 10 minutes, which makes observations very efficient, because we can decide on the fly which instrument to use depending on the conditions.


One of the Nasmyth foci in UT3 is now empty. It used to be occupied by VIMOS, an instrument that we recently decommissioned to make room for a new instrument arriving soon. In the meantime, that focus is empty, and last night the engineers decided to put a screen to project the Moon during twilight. Cool, huh?

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Taken on November 12, 2018