A description is given of a newly-installed computer-operated image scanning and data system for the 150-foot Tower Telescope at the Mount Wilson Observatory. This new system provides improved flexibility, accuracy, and reliability in the magnetograph observations.
I. Introduction
Since 1957 the magnetograph at the Mount Wilson 150-foot Tower Telescope has operated to provide full-disk magnetic scans of the Sun, fine scans of active and quiet regions of the Sun, and other observations. Since 1967 the daily magnetograms from Mount Wilson have appeared in the monthly bulletin Solar-Geophysical Data, published now by the Environmental Data Service of the U. S.
National Oceanic and Atmospheric Administration. The magnetic synoptic charts, drawn from the same data, are published in the I.A.U. Quarterly Bulletin on Solar Activity.
Because these data are used by many investigators, it is of interest to document changes made in the equipment from time to time. I have recently published a detailed chronology of the improvements made to the Mount Wilson magnetograph through 1973 (Howard, 1974). This paper adds to the list a major change in the electronic instrumentation made during 1974.
This computer-operated telescope control and data collection system was put into operation on 4 April 1974. Because of some initial problems, it was replaced again by the old system on 19 April 1974, and the new system was installed finally on 11 July 1974.
One of the principal objectives of the solar program at Mount Wilson is to provide synoptic observations of the Sun which may be compared from one epoch to another. This cannot really be done without keeping the instrument unchanged. The temptation to take advantage of technological advances is stronger than the desire to maintain observations of consistent quality. If it were not so, we would be observing with very crude instruments indeed.
A price we pay for rapid technological advance is that often by the time a complicated new instrument is installed it is obsolete. This system is no exception. However, it is a considerable improvement over the old hard-wired logic system in flexibility and reliability, although the reliability is still not as good as we would like, and this system is likely to be the basis for the Mount Wilson magnetograph for some years to come.