by Helio C. Vital
Analyses of Midcrater and Limb Timings
Dimensions of the Umbra
Our analyses of 61 selected timings made by 3 skilled observers of the Observational Astronomy Network have yielded the following umbral enlargement factors: 1.76+-0.05% (immersions) ; 1.61± 0.06 % (emersions) and 1.691+-0.039% (overall), equivalent to a 1.21+-0.03% increase in the lunar parallax and corresponding to a mean altitude of 77 ± 3 km for the optically active edge of Earth`s atmosphere. That figure is significantly lower than our current overall mean of 92 km. Would that be an indication that the eclipse was effected by higher-than-normal atmospheric concentrations of ozone that could have caused the umbra to shrink or should it be attributed to experimental data straggling solely? The data set also provides a range for the oblateness of Earth´s atmosphere: between 1/397 and 1/65 (2 standard deviations) with 1/111 being the most probable estimate. Considering that immersions and emersions probed low and middle latitudes respectively, such oblateness value that is significantly higher than that for the geoid (1/298) would explain (at least in part) why umbral enlargement factors have been found to be lower during emersions.
Analysis of Magnitude and Danjon Estimates
The brightness of the totally eclipsed Moon is primarily determined by how deeply it is located inside Earth`s umbra. In addition it also depends on the global levels of aerosols cast in the stratosphere by strong volcanic eruptions. Our correlation relating eclipse magnitude to the Moon`s brightness at mideclipse predicts mag=-1.7 for that eclipse indicating a moderately dark event. Visual magnitude and Danjon number estimates made by 13 REA`s observers have been analyzed. The Moon´s magnitude at mideclipse has been averaged as -2.2 ± 0.2, which is half a magnitude brighter than predicted. That indicates that Earth`s atmosphere is currently clear of volcanic dust. The minus -0.5 deviation probably indicates that the current global stratospheric level of aerosols is even lower those used to define the "clean" level of the correlation. The brightness of the eclipse on May 04, 2004 also showed a similar result. Those findings suggest that Earth`s atmosphere has remained unusually clean since then.