Coude Auxiliary Telescope User's Guide

Table of Contents

Optical Arrangement
Bore Sighting
FAT-CAT (Wide field acquisition camera)
Image Rotator (Hamilton Manual)

Observing Hints (Hamilton Manual)
Old Cat Manual
Hamilton Spectrograph Instrument Manual

Data Archive
Mt. Hamilton Homepage

Weather Limits

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 responsibility of the Observer 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 enclosure if they deem it necessary to protect the telescope.

Wind Limits

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

If you have closed the enclosure for wind, a reasonable rule of thumb is to wait 20 to 30 minutes after the winds have subsided to re-open the enclosure. If in doubt about when it is safe to reopen the enclosure after a wind closure, consult the Shane Telescope Operator.


If you have closed the enclosure 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 enclosure. If in doubt about whether conditions have dried out enough to safely open the enclosure, consult the Shane Telescope Operator.

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. The particle counter responds to outside changes, even when the enclosure is closed. The following threshold values (adopted 2013-08-05) apply (even when the Shane enclosure is closed):

0.3 micron 0.5 micron
Warning 12000 800
Closure 17000 1000
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 Enclosure

If snow has accumulated on the enclosure and not been shoveled, keep the enclosure closed to prevent snow from falling or blowing onto the telescope. Contact the Shane Telescope Operator or a Support Astronomer if you are unsure of the state of the snow on the enclosure.


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. The Shanen 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,
Last modified: Mon Aug 17 00:10:53 PDT 2015