THE SOUTHWORTH PLANETARIUM
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Founded January 1970
Julian Date: 2459262.18
2020-2021: XCI
THE DAILY ASTRONOMER
Tuesday, February 16, 2021
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.
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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.
October 7, 1949
October 18, 1967
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.
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:
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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