When to Close

• High Winds If the wind is gusting to above 30 mph, or the 5 min average wind velocity exceeds 15 mph, the doors and roof must be closed. The wind velocity is printed out in the top center of the operators status display. The top number is the immediate value, the second number is the 1 minute average, the third number the 5 minute average, the forth number is the hour gust, and the bottom number is the 24 hour maximum value of a gust.

  If the limit is exceeded, then the appropriate display changes to red. The telescope will be stowed and close the doors. Then consult with the operator about when it will be safe to open.

   

• Moisture Accumulation In or On the Dome: If the outside railings or the door panels show signs of dew or ice, close the building. If the 225 GHz opacity (or T_sys) shows a sudden change, it is necessary to step outside to check the sky conditions. If the conditions are threatening, then we may have to close. We will close immediately if it starts to rain or snow. Clear any accumulation before resuming. We have a rain gauge-which will warn you if it starts raining. However, we should be closed BEFORE it rains. The reason is that the doors take a long time to close. We will have to wait for a while (at least 60 minutes) after the rain/snow stops before observing again.

   

• Humidity Above 95%: Close if the relative humidity gets above 95%. Observers can open again if humidity drops to 90% (and it is not snowing or raining!). We now monitor the VATT weather information and use that to make further judgments about the conditions outside.

   

• Sun on the Dish: The sun safety circle for the SMT is 30 degrees. Software is installed to prevent moving within this circle. However, if the drive has been disabled, it is still possible to have the sun drift into the safety limit. Thus, be aware in the daytime where the telescope and where the sun are if we happen to wander upstairs to tune!

  A CCD camera has been mounted on the telescope to detect the sun within a circle of 29 degrees; if it detects the sun, an alarm will sound throughout the building. Run (don't walk) up to the control room and help move the telescope to a safe position. Tell the operator what you did and he will punish you accordingly.