THE SOUTHWORTH PLANETARIUM
70 Falmouth Street      Portland,Maine 04103
(207) 780-4249      usm.maine.edu/planet
43.6667° N    70.2667° W  Altitude:  10 feet below sea level Founded
January 1970
2021-2022: VIII
"Keeping a steady eye on a complex sky."

THE DAILY ASTRONOMER
Tuesday, September 14, 2021
November's Micromoon Eclipse Part II: The Two Diagrams

We love maps and diagrams with a flaming passion because they are designed
to convey an immense amount of information with the fewest number of
symbols possible. A well-crafted little sheet can encapsulate pages and
pages of information. Today's lunar eclipse article focuses on the diagram
below which consists of a diagram and a map or, if you prefer, two diagrams
in one.


[image: LE2021-11-19P.gif]

The two concentric circles in the center show Earth's inner shadow (the
umbra) and the outer shadow (the penumbra). The straight line slicing
across the circles shows the moon's path from the time just prior to the
eclipse to just after.
The smaller circle represents the moon to scale relative to the shadows.

*PARTIAL:*
We here define four types of lunar eclipse. A *total lunar eclipse* occurs
when the entire moon enters Earth's umbra, or inner shadow. A *partial
lunar eclipse* occurs when only part of the moon passes through the umbra.
A *penumbral eclipse* happens when the moon passes entirely into Earth's
penumbra, outer shadow, but does not touch the umbra. Finally, a *partial
penumbral eclipse* occurs when only part of the moon moves into the
penumbra. This eclipse is partial because the moon's southern limb will not
enter the umbra.

*SAROS 126:*
Every eclipse is part of a Saros cycle. Each eclipse within a given saros
shares the same "geometry" as the other eclipses within that series. (We
are going to devote ALL of Wednesday's DA to discussing the Saros cycle in
more detail.) Successive eclipses within the same Saros series are
separated by 18 years and 11 days. The previous Saros 126 lunar eclipse
occurred on November 9, 2003. The next Saros 126 lunar eclipse will occur
on (well, can you guess?)*

The first Saros 126 eclipse, a partial penumbral, happened on July 18, 1228
and the last will occur on August 19, 2472.
*A NODE:*
This stands for "ascending node." Lunar eclipses can only occur when the
moon is at opposition (full) around the time it reaches a *node, *an
intersection connecting the lunar orbit and Earth's orbit. Intersecting
orbits produce two nodes, one at which the orbiting body passes north of
the parent body's orbital plane (the *ascending node*) and one at which the
orbiting body passes south of that plane (the *descending node*).

[image: Nodes.PNG]
As this eclipse series occurs at the ascending node, the path of each
eclipse will be slightly lower than the one that preceded it.   Conversely,
the path of each eclipse within a series occurring at the descending node
will be higher than the path of the previous eclipse within that series.
   We will discuss this matter in greater detail in tomorrow's Saros
article.


*PAR = 208 m*
Simply, the duration of the partial umbral eclipse.

*GAM = - 0.4552*
This gamma term pertains to the distance separating the moon's center and
the umbra's center at the moment of maximum eclipse.  The unit is Earth's
equatorial radii.

*9:04 TD*
The time of maximum eclipse. The TD refers to *terrestrial dynamical time*,
which is based on atomic time that is unaffected by external factors, such
as irregularities in Earth's rotation.

*Delta T = 70 s*
The time difference between dynamical time and universal time resulting
primarily from Earth's rotational irregularities.

*U. Mag = 0.9742*
Umbral magnitude equals 0.9742.  This magnitude measures the percentage of
the moon's diameter immersed in the umbra.  97.42%

*P. Mag = 2.0720*
Penumbral magnitude.  The fraction of the moon's diameter immersed in the
penumbra.    This value is measured from the edge of the penumbra to the
point on the moon that is in the deepest part of the shadow.

*THE SECOND DIAGRAM:*
The second diagram, located at the bottom of the above chart, displays a
visibility map: regions where the eclipse is totally visible, partially
visible or not visible at all.

The areas steeped in the darkness (most of Africa, the Middle East,
Antarctica, regions in Russia and Europe) won't see any of the eclipse
because the moon will not be above the horizon at those locations.

Observers within the areas covered in darker grey strip at either side of
the dark region will only see the penumbral eclipse, i.e. not much at all.
  For instance, a moon watcher in extreme western Australia will see the
penumbral eclipse ending as the moon rises.  Meanwhile an observer in
Morocco would see the penumbral eclipse beginning as the moon sets.

Observers within the lighter (and wider) grey areas will see some of the
umbral eclipse.  Most observers in Australia will see the umbral eclipse in
progress as the moon rises.    Those Australian sky watchers farther to the
east will see more than those in the west.     Meanwhile, most South
American observers will see only part of the umbral eclipse before the moon
sets.     Eastern South American sky watchers will see less of it than
those farther west.

Observers within the grey stripes next to the white regions will see almost
all of the eclipse.     Those observers in eastern New Zealand will see the
moon rise during the first penumbral phase so they will see the rest of
it.  Those observers in eastern North America (including here in Portland)
will see the moon set during the last penumbral phase.    (We won't miss
much.)

Finally, observers within the white regions including almost all of North
America and northeastern Russia will see all of the eclipse.

All of that information contained within a small rectangle.

Tomorrow, our lunar eclipse week continues with what we hope will be a
clear explanation about the Saros cycle.


*November 30, 2039.



To subscribe or unsubscribe from the Daily Astronomer:
https://lists.maine.edu/cgi-bin/wa?SUBED1=DAILY-ASTRONOMER&A=
<https://lists.maine.edu/cgi-bin/wa?SUBED1=DAILY-ASTRONOMER&A=1>