Possible Effect of Mount Reventador`s Nov 03, 2002 Eruption on the

Brightness of the 2003 and 2004 Total Lunar Eclipses

by  Helio C. Vital (Eclipses Section/REA/Brazil) 


The idea of using total lunar eclipses as indicators of global levels of aerosols of volcanic origin was originally proposed by Richard Keen who has successfully proved its feasibility. According to Keen, strong volcanic explosions may darken total lunar eclipses considerably. The author has used published data as well as REA`s observations covering a total of 24 eclipses (1956-2001) to get a correlation between umbral eclipse magnitude (Umag) and the Moon`s magnitude (Mag) and apparent radius (SD, in arc minutes) at mid-eclipse. The events found to be definitely affected by volcano explosions were left out of the input data used to obtain a second similar correlation for aerosol-free events only. The resulting improved correlation (r2=0.88) is:

                                                                      Mag = -1.9 + 4.3 Umag - 5 log(SD)  

                                            (updated on April 16, 2014 to account for current observed magnitudes at U2 and U3 that indicate a 0.5-magnitude lower baseline)     


It has been used it to predict the Moon`s magnitude. Comparing such predictions with estimates made by several REA`s members who used a perfected version of the reversed binoculars method to obtain the Moon`s  magnitude during the eclipses in May and Nov., 2003 and May and Oct., 2004 yielded the table and plot shown below. The magnitude differences found have been plotted as a function of time elapsed since the explosion of Mount Reventador in Ecuador on November 03, 2002 (volcanic explosivity index=4) that injected a significant amount of aerosols into Earth`s stratosphere.



Eclipse Date

Umbral Eclipse Mag (Umag)

Moon`s Observed Mag (O)

Moon`s Predicted Mag (P)

Δ (O-P)


Optical Thickness (±0.005)

May 16, 2003






Nov.09, 2003






May 04, 2004






Oct. 28, 2004







The data seem to consistently indicate that two years after the eruption the global level of stratospheric volcanic aerosols dropped to a level assigned as ¨aerosol-free¨ by the correlation and has remained so up to the present.  

Analyses of the observation data from the April 15, 2014 total lunar eclipse, for example, yielded Mag= -3.2 for the magnitude of the Moon at mid-totality compared to a Mag= -2.3 prediction. That gives an optical thickness of -0.023. That figure is an indication of an aerosol-free stratosphere. 




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Copyright [email protected] C. Vital


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