Total Lunar Eclipse on May 15-16, 2022

Preliminary Findings from Observations

Helio C. Vital

(1)               Was the eclipse dark? Yes.

(2)               Was the eclipse extremely dark? No.

(3)               Was the Moon at mid-totality approximately as dark as predicted based only on its path across the umbra? Yes, roughly. Probably, a bit darker though.

(4)               What were the estimades made by the Brazilian Team of observers for the brightness of the Moon at mid-totality? Preliminary means for Danjon and magnitude estimates made by Brazilian observers consistently indicated a relatively dark eclipse.

They were: L=2.0 (±0.5) and m= -0.8 (±0.3), respectively.

The author`s estimates for mid-totality were: the Moon was roughly 1.8 times brighter than Alpha Centauri and ~4 times brighter than Antares. Both comparisons yield m=-0.8±0.2. He chose to assign different Danjon (L) Numbers to the Southern (brighter, pale orange colored) and the Northern (darker and mostly colorless) parts of the Moon`s disk. They were: 2.5 and 1.5, respectively. Since the selected areas covered 45% and 55% of the disk, his estimate for the Moon was: L = 2.5 x 0.45 + 1.5 x 0.55 =  2.0

The observers were: Alexandre Amorim, Willian Souza, Helio C. Vital, Antonio Padilla, Caio Correia, Cledison Silva, Luiz A. Araujo, Niercey Justino and Paulo Fernandes.

(5)               What would be the magnitude of the Moon at mid-eclipse if the stratosphere were free of aerosols? A correlation derived by the author provides the mid-totality visual magnitude of the Moon for a given umbral eclipse magnitude. It is:

m(U) = - 2.0765*U2 + 10.334*U - 11.70   (Vital, Helio C.)-----   Based on data from 11 observed eclipses with clean stratosphere  (r2=0.999).

For the umbral magnitude U=1.415 of the eclipse, it yields m=-1.23.

(6)               Why was the eclipse unusually dark? Because the Moon penetrated deeply into Earth`s umbra, more than in most eclipses. Due to the fact that the inner umbra is darker,  less sunlight reached the Moon there.

(7)               The additional darkening of the Moon of only 0.4 (±0.3)((=1.2-0.8) magnitude could be attributed to Tonga aerosols? Possibly.  In case it was indeed caused by Tonga aerosols it would be more compatible with a VEI (volcanic explosivity index)=4  eruption 4 months ago, rather than a VEI=5 (on which the author had based his estimate). However, since the magnitude difference is very small, it could also have been caused by excessive cloudiness along Earth`s limb or uncertainties in the correlation and/or also in the observed magnitude. For example: Tony Mallama`s prediction was m=-0.5, for this eclipse. That would eliminate the need for any volcanic effect at all. However, the author still favors the assumption that Tonga slightly darkened the eclipse, considering the huge amount of material still lingering in the stratosphere and producing amazing color displays at twilight worlwide.

(8)               The darkening effects of Tonga aerosols will also be observed during the lunar eclipse in November?  Volcanic aerosols can linger in the stratosphere for many months. However, with basis on what happened during the eclipse in May, the author expects the effect from Tonga`s eruption to be very small (possibly 0.2±0.2) during the total lunar eclipse of 2022 November 08. On the other hand, since the eclipse will also be central, he predicts the Moon will be shining at m= -1.3±0.5 at mid-totality if no other stratospheric eruption occurs. That would also correspond to a moderately dark eclipse.