A PRELIMINARY ANALYSIS OF OBSERVATIONS OF
THE
2021 NOV 19 DEEP PARTIAL LUNAR ECLIPSE
By Helio C.
Vital
Brazilian Observers
Mostly Clouded Out
Most skilled lunar
eclipse observers in Brazil were prevented from watching the deep partial
eclipse of Nov. 19, 2021 due to bad weather. As a consequence, only one
observation report has been received by Lunissolar so far.
Measuring the Atmospheric Contribution
to the Umbra: A Unique Report
Advanced observer Alexandre Amorim amazingly managed to time a few immersion contacts as he meticulously
monitored the very low partially eclipsed Moon through clouds. His report
included the following immersion contact times (UTC), listed next to the
corresponding enlargements in Moon`s parallax calculated by the author: U1
(07:18, 1.7%), Riccioli (07:30:50, 1.85%), Grimaldi (07:33:08, 1.95%) and Copernicus (07:42:07,
0.82%).
Impressions from the Livestream
by Griffiths Observatory: a bright red-colored eclipse
By watching the livestream from Griffith
Observatory, the author noticed
a moderate red coloration prevailing in the Moon`s disk inside the umbra, in
addition to several other subtle hues. Indeed, the eclipse was bright and that
apparently led some observers to readily compare it with previous total
eclipses and rate it as very bright, somewhat ignoring the fact that it was
partial, albeit a very deep one (U=0.975), meaning that the Moon`s path across
the umbra was indeed expected to be shallower and thus primarily less dark in
comparison with total eclipses. By the way, In 2015, Lunissolar estimated some 85% chance that the longest partial
lunar eclipse in centuries was in fact the one that happened on 2015 April 4.
Brightness of a Similar Eclipse with a
Clean Stratosphere
Using a correlation m=U*(2.08U-10.34)+11.7 (r²=0.998) derived by the author from analysis of past eclipses not affected by
stratospheric volcanic aerosols, it can be estimated that the mid-eclipse
visual magnitude of the Moon for an umbral magnitude
(U) of 0.975 would be m=-3.6±0.3. In addition, considering that for a barely
total eclipse the Moon would typically dim to m=-3.4±0.3, it can be concluded
that the bright cap inside the penumbra would have caused the Moon to appear
0.2 mag brighter. Such event would have been an
amazingly bright and colorful eclipse indeed. However, was that really the
case?
Lunissolar Predictions: Eclipse Moderately
Darkened by Aerosols from La Soufriére Eruptions
Based on his study
of 50 lunar eclipses with observed brightness data available, the author had
posted on Lunissolar on June 28, 2021, a project of
observation for the 2021 Nov. 19
lunar eclipse, predicting an additional 0.9±0.3 magnitude drop in the Moon`s
brightness due to the likely presence of lingering aerosols launched in the
stratosphere by eruptions in April of the St.
Vincent La Soufrière volcano. A possible residual contribution from other volcanoes was also
mentioned.
Stratosphere Currently Not Clean: The
Findings by NASA`s Sage III Team
As announced by NASA, the Stratospheric Aerosol and Gas Experiment (SAGE) III on the
International Space Station (ISS) has recently detected two enhanced layers of
aerosols in the stratosphere. A higher one, at an altitude of 22 km, composed
of sulfate droplets remaining from the eruption of the
La Soufrière volcano in April 2021 and another layer, at 17 km, attributed to remnants from the August
eruptions of the Fukutoku-Okanoba undersea volcano. In spite of its lower concentration, the impact of the higher layer is
expected to be larger since it corresponds to the altitude where our
atmosphere, backlit by the Sun, is most brilliant as seen from within the
eclipsed umbra.
A Sole Visual Magnitude Estimate
Available
Published estimates
of lunar eclipse brightness and contact timings are currently rare and the lack
of visual observations has severely limited advances in the understanding of
the dynamics of lunar eclipses and the predictability of their characteristics.
Fortunately, a very experienced observer posted an outstanding observation report that included his magnitude estimate for
the Moon at mid-eclipse as m=-2.5±0.5, as well as his rating in the Danjon Brightness Scale: 3.2±0.3.
Estimating the Brightness of the
Eclipsed Moon from Photos
While analyzing a
few wide-angle high-resolution photos at mid-eclipse showing the eclipsed Moon
next to the Pleiades, published on the SpaceWeather gallery, the author found that the Moon`s disk in the images displayed at 12%
magnification became barely noticeable on the computer screen as seen from a
few meters away. The same happened to the Pleiades open star cluster (m=1.6)
when the same image was exhibited at a higher magnification (75%).The method
was used for three photos. He then calculated the mean magnitude of the Moon
and the associated standard deviation as m=1.6-2.5*log(75/12)²= -2.4 ± 0.4 (1 
).
Conclusion
The deep partial lunar eclipse
of Nov. 19, 2021 was moderated darkened (~1.2 mag) by
the presence of lingering volcanic aerosols from April`s VEI 4 eruptions of the
La Soufrière volcano (0.9±0.3 mag), possibly added to a smaller effect
of 0.3±0.2 mag due to
the August eruptions of the Fukutoku-Okanoba
undersea volcano.
At greatest eclipse,
the Moon was shining at m=-2.4±0.4, rather than at -3.6, that would be the case
if the stratosphere were clean. That figure corresponds to an L=2.9±0.3 rating
in the Danjon Scale of lunar eclipse brightness.