We will skip today's mythology simply because the article is so extensive
in both text and graphics.   Our apologies to those subscribers who only
open these silly things for the mythological excursions.

THE SOUTHWORTH PLANETARIUM
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Founded January 1970
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2020-2021:  XCI

THE DAILY ASTRONOMER
Tuesday, February 16, 2021
Exploratorium XXIV:  November 2021 Lunar Eclipse II

During today's Exploratorium, we continue our discussion about the partial
lunar eclipse that will occur on November 19, 2021.    Our focus will be on
the graphic featured below.  Developed by eclipse wizard Fred Espenak, this
chart provides basic information pertaining to the eclipse we will
hopefully be able to observe in November.

[image: unnamed (1).gif]

We will proceed clockwise through the chart beginning at the upper left.

*PARTIAL:*
    A partial lunar eclipse is one in which the moon does not entirely
enter the umbra, the inner part of Earth's shadow.          Although this
eclipse will be partial, most of the moon will still pass through the
umbra, making it look similar to a total lunar eclipse

*SAROS 126:*
Every eclipse is part of a Saros cycle.  Successive eclipses within this
cycle occur every 18 years, 11  days and 8 hours.      Saros 126 contains
70 eclipses, the first of which occurred on July 18, 1228.  The last one
will happen on August 19, 2472.         The previous Saros 126 lunar
eclipse (the last total lunar eclipse in the series) occurred on November
9, 2003.

*A NODE*
The eclipse occurs around the "ascending node." A node is the intersection
between the moon's orbit and the ecliptic.   The ascending node marks the
point at which the moon is above to move "north" of the ecliptic.   The
moon moves south of the ecliptic plane when it is at the descending node.
   Note that each successive eclipse in an ascending node lunar saros
migrates "downward."   The following sequence consists of images showing
the moon's path during successive Saros 126 eclipses in 1949, 1967, and
1985, respectively.

[image: Lunar_eclipse_chart_close-1949Oct07.png]
*October 7, 1949 *

[image: Lunar_eclipse_chart_close-1967Oct18.png]
*October 18, 1967*

[image: Lunar_eclipse_chart_close-1985Oct28.png]
*October 28, 1985*

The following Lunar 126 eclipse (November 9, 2003)  was the last total
eclipse of the series.   During that event, the moon was immersed in the
umbra, albeit briefly.    The November 19, 2021 eclipse won't be total
because at maximum eclipse, a small southern sliver of the moon will remain
outside the umbra.
(We'll discuss the Saros in more detail tomorrow.)

At the upper right hand corner one sees information related to the time and
date of maximum eclipse.   *Maximum eclipse* is the moment at which the
distance separating the center of the moon and that of Earth's umbra is at
a minimum.

Date when the maximum eclipse occurs:  2021  November 19. The time when the
maximum eclipse occurs :  9:04 TD
TD refers to Terrestrial Dynamical Time, based on the highly precise atomic
clock time keeping.
The delta T value below it refers to the discrepancy between the
Terrestrial Dynamical Time and Universal Time, or the time along the prime
meridian that runs through Greenwich.

* U. MAG*
Umbral magnitude.
The percentage of the moon's angular diameter that is immersed in the umbra
at the moment of maximum eclipse.       The umbral magnitude is 0.9742
meaning that 97.42% of the moon's diameter will be within the umbra.
 Important note: the magnitude is different from the obscuration
percentage.  While these values are essentially the same when the magnitude
is close to 1, the difference becomes significant at lower values:

[image: download.jpg]
For instance, when an eclipse magnitude equals 0.5,  half of the moon's
diameter blocks the Sun.  However, less than half of the Sun is covered, so
the obscuration is less than 50%.

*P MAG*
Penumbral magnitude
At maximum eclipse, the penumbral magnitude is 2.07, meaning that 207% of
the moon's angular diameter is covered.  What could this value possibly
mean?  Well, at maximum eclipse, one could fit two full moons and a length
of space equal to seven percent of the moon's angular diameter within the
penumbral shadow.

*MAP*
The map at the bottom shows the visibility regions.   Observers in
locations colored white in the map will be able to observe the entire
eclipse.   Examples: almost all of the United States, Canada, and Mexico.
      Observers in dark regions, such as most of Africa, the Middle East,
and parts of Asia won't see any of the eclipse at all.     Notice that the
map includes three strips with various shadings.   Maine, for instance, is
located within the strip adjacent to the white region.   That means that
observers in Maine and the other areas inside this strip will see the moon
set during the second penumbra phase of the eclipse.    Observers within
regions inside a similarly colored strip at the other side of the map, such
as within the northern part of New Zealand, will see the moon rise during
the first penumbral phase of the eclipse.     Almost every South American
observer will see the moon set during the umbral eclipse just as nearly
every Australian observer will watch the rise  during the umbral eclipse.
Observers within the strip just to the west of the dark region will see the
moon set during the first penumbral phase (examples: northwest Africa, most
of Europe). Those  observers along the strip just east of the dark area
(example:  wesrtern parts of India) will see the moon rise during the
second penumbral phase.

*GAMMA*
The distance, in units of Earth's equatorial radius, between the center of
the shadow cone and the moon's center at the moment of maximum eclipse.  If
the shadow cone passed directly over the moon's center, the gamma value
would be zero.     In this instance, the value is negative because the
moon's center is passing south of the shadow cone.

*PAR  *
The duration of the partial lunar eclipse.    This one lasts for 208
minutes.   Had this event been a total lunar eclipse, the chart would have
included a time for the duration of totality.



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