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:

  1. 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.

  2. 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.
  3. 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.
  4. Go to the special observing plans for more bright targets.