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Ángel R. López Sánchez was observing at the Australia Telescope Compact Array in 2008.
He describes how this photo came about:
"After a long day I walked
from the control building to the lodge and saw a beautiful moon
halo. I ran to my room and grabbed my camera (CANON EOS 400D, the digital
camera I got as a gift from my IAC colleagues when completed my PhD)
and tripod and looked for a nice position with one of the ATCA
antennae (CA03 in this case). The halo didn't fit within a single
exposure, so I took several images and merged them in a single final
exposure."
Lunar halos are have a radius of approximately 22 degrees halos (which is why they don't fit in a single exposure!).
They are created when the moonlight is refracted by ice crystals in thin cirrus clouds.
Similar "22-degree halos" can be seen around the sun when conditions are right.
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