Nickel 1-m Telescope Manual: Weather Limits

Weather Limits

Nickel observers should be aware of the following conditions which limit or prevent operation of the telescope. Several weather monitors are available for various locations on Mount Hamilton. Refer to Lick Observatory Weather to get real-time readouts of the local weather conditions. It is the observer's responsibility to monitor the weather and ensure that the telescope is protected from the elements so that no harm comes to any of its systems.

Note that these limits are only guidelines. Observatory staff members may instruct you to close the dome if they deem it necessary to protect the telescope.

Wind Limits

Average (MPH) Persistent Gusts (MPH)

Into Wind 35 40

Crosswind 40 45

Downwind 45 55

Exercise caution using windscreen as windspeeds approach limits.

If you have closed the dome for wind, a reasonable rule of thumb is to wait 20 to 30 minutes after the winds have subsided to re-open the dome. If in doubt about when it is safe to reopen the dome after a wind closure, consult the 3-m telescope technician.

Humidity

94% relative humidity, or
when dew sensor alarm sounds above 0 degrees centigrade, or
as necessary to exclude moisture from the dome.

Note: If the humidity is greater than 80% the ventilation fans should be turned off to prevent excessive moisture from entering the dome.

If you have closed the dome for humidity, a general rule of thumb is to wait until the humidity has dropped well below the limit and things are drying out (e.g. humidity is 85% or below for 30 minutes) before reopening the dome. If in doubt about whether conditions have dried out enough to safely open the dome, consult the 3-m telescope technician.

Airbourne Particles/Ash

Enclosures must be closed if airborne particles (e.g. ash from forest fires) are deemed a threat to the optics. A particle counter resides inside the Shane enclosure and measures particles 0.3 microns in size and 0.5 microns in size.
A second particle counter resides outside the APF dome and measures particles 0.3, 0.5, 0.7, 1.0, 2.0, 3.0, 5.0, and 10.0 microns in size.
The interior particle counter responds to outside changes, even when the enclosure is closed. The following threshold values (adopted 2013-08-05, updated 2021-03-4) apply (even when the Shane enclosure is closed):

	0.3 micron	0.5 micron	0.7 micron	1.0 micron	2.0 micron	3.0 micron	5.0 micron	10.0 micron
Warning	12000	1120	307	192	77	19	7	2
Closure	17000	1400	400	240	96	24	8	3

Particle counts must remain consistently below the closure thresholds for at least 30 minutes before (re-)opening enclosure can be considered.

If in doubt, contact the Shane telescope operator (8-0652).

Snow on Dome

If snow has accumulated on the dome and not been shoveled, keep the dome closed to prevent snow from falling or blowing onto the telescope. Contact the 3-m telescope operator or a support astronomer if you are unsure of the state of the snow on the dome.

Lightning

If distant lightning can be seen but no thunder heard, there is no immediate threat and observing may continue provided there is no danger of rain.

If lightning is 10 miles away or less (about 50 seconds from lightning to thunderclap), there may be a danger of a strike. Telescope operator can stop observations to shutdown critical electrical systems at his or her discretion.

Wait at least 30 minutes after the last audible thunderclap before declaring the storm passed and resuming operations.

Support Astronomers, sa@ucolick.org

Last modified: Wed Mar 10 15:18:13 PDT 2021

User's Guide to the Nickel 1-m Telescope

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