Abstract
CONDITIONS FOR BEST TELESCOPIC DEFINITION.—Dr. T. J. J. See brings together a few facts and remarks regarding the conditions essential to good seeing with large telescopes and high magnifying powers (Astr. Nachr., No. 3438). These are based not only on his own experience under very favourable circumstances during the past year, but many of the suggestions developed are, as he says, the outcome of Mr. Douglass' work on atmospheric currents and their relation to astronomical seeing. At the Harvard station in Peru the seeing at three o'clock in the morning was nearly always bad, caused, as was discovered, by a current of cold air from the valley draining the great mountains above and rushing down the adjacent gorge flowing over the observatory, and completely ruining the seeing almost instantaneously. Such currents as these must always be avoided when fixing upon a position for an observatory, and this is one of many causes which produce bad definition. The country in which good conditions might be depended on should be free from mountains and cyclonic causes which disturb the equilibrium of the atmosphere. A high and dry table-land, distant from oceanic influence, like the northern part of Arizona, presents conditions which are almost ideal when snow is not present. Mountain sites are always less satisfactory than broad table-lands, because currents forced up from below are cooled by expansion due to diminished pressure, and rapid changes are likely to take place when the wind is strong. When covered with snow and overflown by currents of a different temperature, mountain sites are wholly incapable of giving good definition.
Article PDF
Rights and permissions
About this article
Cite this article
Our Astronomical Column. Nature 56, 386 (1897). https://doi.org/10.1038/056386a0
Issue Date:
DOI: https://doi.org/10.1038/056386a0