User's Guide to the Shane 3-m Telescope

Table of Contents

Diagonal Mirror
TUB Rotation
Arc & Flat-field Lamps
trouble report
Target Of Opportunity (TOO)
Remote Operations
Data Archive
Mt. Hamilton Homepage

Weather Limits

3-meter observers should be aware of the following conditions which limit or prevent operations of the telescope.

Temporarily Enhanced Limits Imposed 2020-10-01, Removed 2021-01-07

The temporary closure limits imposed in the aftermath of the 2020 SCU Lightning Complex wildfire have now been lifted. We have thus returned to the pre-fire limits for wind, humidity, and dewpoint.

Current Limits

Note that these limits are only guidelines.
The decision to open or close the dome is entirely at the discretion of the telescope operator.

Wind Limits

Average (MPH)Persistent Gusts (MPH)
Into Wind3540
Exercise caution using windscreen as windspeeds approach limits.


94% or at the telescope operator's discretion based on blowing fog, condensation on dome and handrails, etc..

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 2021-03-04) 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, the telescope operator will keep the dome closed to prevent snow from falling or blowing onto the telescope.


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 as his or her discretion.

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

Last modified: Wed Mar 10 15:11:44 PDT 2021