From Alan Fitzsimmons
I read with interest your article about the proposal by astronomers Ivan
Baldry and Joss Bland-Hawthorn to use polarising filters to reduce glare from
the Moon. However, large optical telescopes do not “sit idle” for 15 nights each
month, as your reporter seems to believe
(14 April, p 11).
Although much fainter objects can be seen in “dark time”, there are many
scientific programmes that can be performed in moonlight, as long as the target
is a fair distance from the Moon in the sky.
For example, during a full Moon the British William Herschel Telescope on La
Palma can observe objects a million times fainter than are detectable by the
human eye on a dark night, using an exposure time of just 30 seconds. So, due to
the overwhelming demand, the facilities are used by astronomers every clear
night. Of course, astronomers need to check that their targets are not actually
behind the Moon when they try to observe them!
Ivan Baldry writes: It is correct that plenty of observations are undertaken
while the Moon is up. For those interested in observing extremely faint objects
(background-limited observing), a polariser could improve imaging during these
bright Moon phases.
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