Why clouds cancel your booking, and what happens next

A telescope cannot see through cloud. It also should not be left open in rain or high wind, which can damage it badly enough to take a site offline for weeks. So when conditions turn unsafe, observing stops.

What happens depends on how you booked

There are two ways to book, and weather treats them differently on purpose.

Earliest available

You are in a queue. If tonight is clouded out, you stay exactly where you were in that queue and run on the next clear night. You do not lose your place, and you do not have to do anything.

A specific time

You reserved one particular slot. If that slot is clouded out, the booking is cancelled and you can book again. We do not quietly move you to a different night, because that night belongs to somebody else, and because you chose your time for a reason we cannot guess at.

A cancelled booking costs you nothing

Weather cancellations do not use up your observing allowance, and they do not trigger the quiet period that normally follows a completed session. Nothing was observed, so nothing is counted.

Why we are cautious

The people who look after each site decide when conditions are safe, and their decision stands. If we cannot tell what the weather is doing — a sensor has failed, or a site has not reported in — we treat that as unsafe and do not observe. Not knowing is not the same as being fine.