STETSON DISCOVERS WIDE VARIATION OF LATITUDE CAUSED BY POSITION OF MOON

Working at the Astronomical Laboratory on Jarvis street with thousands of observations of latitude, Professor H. T. Stetson, with the assistance of Miss Margaret Olmstead, a graduate student at Radcliffe, has discovered a remarkable variation in the latitude of a place on the Earth's surface dependent on the rising and setting of the moon. This information was made known to a CRIMSON reporter yesterday.

That this discovery is likely to become a matter of considerable importance to astronomers and also to geologists and geophysicists as made evident by the fact that the variation is nearly ten times that which thus far can be accounted for on theoretical grounds.

Dulrnal Effect Unknown

A slow progressive shift of the axis about which the earth rotates over a period of months and years has been known for a long time, explained Professor Stetson, but that there should exist such a diurnal effect depending upon the altitude of the moon in the sky was not known until the results of the present investigation were found. From the results of other investigations in progress at the Astronomical Laboratory last year, Professor Stetson is led to believe that the moon might cause a deviation in the direction of gravity as it passed over the meridian of the observer. The most delicate test for a change in the direction of the vertical is to be found in the precise observations of stars for latitude. A photographic zenith telescope locates the position of the zenith with respect to the stars with the order of accuracy of about a hundredth of a second of arc, which corresponds to a foot on the earth's surface. Several thousands of such observations for latitude were made some time ago by Ross at Gaithersburg, Maryland, one of the stations of the International Latitude Survey. It was the recent analysis of this series of observations that brought to light the variation of nearly a tenth of a second of arc in latitude, depending upon the altitude of the moon. The maximum value occurs when the moon is 30 degrees above the horizon.

Preliminary Statement Made

A preliminary statement of the results was given in a paper by Professor Stetson and Miss Olmstead at the fall meeting of the American Astronomical Society at Amherst. Since then the investigation of thousands of observations for latitude of the Naval Observatory at Washington has been analyzed at the Harvard Laboratory and Dr. Stetson announces this appears unmistakeably to affirm the results of his previous study. The fact that this rise and fall of the value in latitude is gradual and systematic and represents a range nearly 20 times the value of the probable error leaves little room for doubt as to the reality of the variation.

Several hypotheses are being considered to explain the phenomena which may be due to a combination of causes. Theoretically a small tide must take place in the earth's crust as the moon revolves about the earth. But from other considerations it is not thought that this can be sufficiently large to account for the observed effect. Professor Stetson is now considering the possible effect of a tidal wave in the earth's atmosphere caused by the moon which may alter the apparent direction of the ray of light from a star and produce the effect noted. The most direct interpretation is that of a shift in the earth's instantaneous axis of rotation. As a last resort it may be necessary to consider movement in the earth's crust, although Professor Stetson was reluctant to affirm this statement until a more extensive study of allied problems had been completed.

The importance, however, of the discovered effect, the astronomer added, need hardly be emphasized, as it is involved in the accurate determination of star positions upon the minute changes of which much of the knowledge of our universe depends. If the change in latitude here noted becomes substantiated by further researches, it will appear necessary to apply new corrections to astronomical observations not hitherto recognized. It may very well be that the discrepancies between the results for the positions of stars from widely separated observatories may be largely explained by this phenomenon.