Barbara M. Middlehurst

Lunar transient phenomena: topographical distribution.

The sites named in nearly 400 reports of lunar transient phenomena fall into three classes: (i) sites peripheral to the maria, (ii) ray craters, and (iii) ring plains with dark or partially dark floors; none are known in the rugged highland area of the southeast (International Astronomical Union, 1964; classically southwest) quadrant. Permanent records are few; the sites where known are consistent with the visual records.

Low-Latitude Noctilucent Cloud of 15 June 1963

A bright noctilucent cloud was observed and photographed north-west of Tucson on 15 June 1963. Results of computations indicate that the cloud was at a height of 71 kilometers. The cloud appears to have resulted from the launching of a Scout space vehicle.

Moonquake predetermination and tides

Abstract A pattern in moonquakes, which correlates with the monthly tidal cycle, also correlates with a phase shifted pattern of a 7-month tidal cycle. The lead of approximately 2 months in moonquake occurrence can be explained if local tidal forces are combined with a moonquake-driving force. This force, assumed to result from the 6-yr physical libration in latitude, would cause N-S sliding of an outer layer across a solid layer within a decoupled core in a lunar model. During 1969–1971, the sliding would be southward with a progression of monthly maxima in the combined forces. Where these forces control moonquakes, the reversal in direction of the 6-year cyclic force in early 1972 should cause a minimum in moonquake activity. Decreases toward such a minimum did occur simultaneously in the similar progressions of monthly moonquakes and maxima in the combined forces at the most active hypocenter. Repetition of the 1966–1971 force pattern in 1975–1977 should produce a corresponding repetition of the moonquake pattern. In 1973, the yet to be determined pattern in moonquakes could correspond to the pattern of either an entirely cyclic force, or a combination of the cyclic force and an additional secular force. The physical libration in latitude controls moonquakes in both cases. If moonquakes are driven by an entirely cyclic force, the use of a simple lunar model could lead to a better understanding of moonquake causes and of possible analogs in earthquake control.