WEATHER SAFETY LIMITS

revised 06/08/98

The dome should be closed when outside humidity reaches 90%, OR when the mirror temperature approaches within 2 degrees of the dewpoint as indicated on the Casella met displays. It should not be opened again until the humidity has dropped to 80%. Warning of humidity on the way may be provided by the main-mast wetness alarm on the met display. This alarm (and other met alarms) can be silenced by typing `A' on the keyboard. Other telescopes should be warned when the local wetness alarm goes off.

In wet weather, the domes should be rotated at the end of the night so that the shutters point into the wind.

In case of ice/snow, the domes should be pointed as follows:

In the event of unusual humidity in the dome during the day (e.g. flagged by the dewpoint alarm of the met system), and if humidity inside the dome exceeds that outside, the dome should be opened until the two equalise.

WIND:
The dome should be closed at the JKT, INT or WHT if the wind speed exceeds (or gusts for more than 10 sec above) 50, 80 or 80 km/h respectively. The appropriate box on the met display will turn red if the limit for the telescope is exceeded, and beeps will sound. The alarm can be silenced by typing `A'. If the met system fails, use a hand-held anemometer. When the speed exceeds the limit, the main risk is of distortion to the dome shutters (particularly the JKT's) rather than to the dome or the telescope (airborne dust is also a possible hazard).

DUST:
If you can see dust in the beam of a torch, close the domes. Don't rely on the dust monitor of the met system.

ICE:
If the dome shows any resistance to movement, don't force it. Never try to chip ice free.