Things to do on Cloudy Nights
The observing plans are generated with the assumption that the sky will be
clear and the seeing will be good. This is not always the case.
But while all clouds affect observations negatively, it is possible to get
good data through thin or even moderately-thick clouds.
In the case of thin clouds you should do the following:
- Increase exposure times for the highest priority targets. Estimate
how much light you are losing. Double or triple the exposure times if they
are reasonable, or take more exposures. If the clouds are patchy, taking more
exposures, rather than longer exposures, will prevent the possibility of
saturating the detector.
If a target cannot be seen on the acquisition TV, do not waste time trying
to observe it. Stick with the brighter targets.
Check the spectra. If there are no counts, it may be too faint for the
conditions.
Drop the lower priority targets.
- If time remains, or no bright targets are above the horizon, go to targets
in the backup list. In thin clouds, try to avoid targets with
air masses larger than 1.5.
- Some targets can profit from long time series exposures. These include
the cataclysmic variables (remark "C") and chromospherically-variable
stars such as AB Dor and S CrA. Feel free to increase the number of
exposures. Check the remarks for such targets.
- Go to the special observing plans
for more bright targets.