Seeing Measurements

 

To ensure that we have a method which enables us to compare one night with another at the Cassegrain focus please adopt the following. One of the seeing measurements must be taken at the zenith around midnight - or after the dome has been open for several hours.

1. Choose a star which appears in or near the field being observed.
2. Focus the telescope (see Section 12.2).
3. Integrate for 128 frames in SUM mode using the slit viewing Grinnell TV.
4. Adjust the TV gain to give an unsaturated image. (The profile of a saturated image shows a flat top).
5. Select MENU (RESTRICTED PROFILE) using the joystick or the SELECT button on the Grinnell control box.
6. Make the Grinnell seeing measure in RA. If the turntable has been rotated use the RA guide button to see where RA lies.
7. Repeat twice more and carry out the whole procedure 4 or 5 times per night. Record in the NA logbook.
8. Note the zenith distance and focus for the measurement in the TOs log.