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: XLIII
"The next time a stranger talks to you when you're alone, just look at them
shocked and whisper, 'you can see me?'"
-attributed to many people
THE DAILY ASTRONOMER
Wednesday, November 17, 2021
Lunar Eclipse Q/A
Yes, indeed! We're going to experience a nearly total lunar eclipse later
this week and believe you me we're Zeus-damned excited about this one, not,
of course, that we'll actually be awake for it, but we are thrilled that
it's happening.
After all, lunar eclipses don't happen every month AND this partial lunar
eclipse will not only be the longest partial lunar eclipse of this century,
but will be the longest partial lunar eclipse in 580 years!
Today we focus on the eclipse yet again by reposting the timeline and
answering some questions we've received about this eclipse and lunar
eclipses, in general.
First, we'll state that the Southworth Planetarium will not be open for
this event as it is occurring in the wee hours, a time when precious few
souls dare to venture down into the tenebrous depths of our subterranean
star dome. (That's probably just as well considering what likely transpires
in this dome when humans aren't observing it.)
Secondly, this lunar eclipse isn't total, as the southern limb of the moon
will remain outside Earth's *umbra,* or inner shadow, as one can see in a
graphic below. However, the moon will still appear quite reddish when most
of the moon is immersed in the inner shadow.
*QUESTION: WHEN WILL THIS ECLIPSE OCCUR?*
For us in the eastern United states, the entire eclipse will occur on
November 19, 2021. However, as noted in the time-line below, observers
won't notice much during the first part of this eclipse
- *1:02 a.m. Penumbral Eclipse begins. *If you wake up just for this
part, you'll be sorely disappointed. The moon's brightness hardly
diminishes at all when passing through the penumbra, or outer part of
Earth's shadow. Apart from the satisfaction of knowing that you're
witnessing a celestial event, the penumbral part will likely not offer much
scintillation or inspiration.
- *2:18 a.m. Umbral Eclipse begins. *Now the action starts! At
2:18 a.m, the moon makes contact with the umbra, defined as Earth's inner
shadow. We can watch Earth's shadow arc migrating across the moon's face.
Initially, it will appear as a fuzzy shade along the lunar limb. That
shadow will soon become sharp and distinct. One can well understand why
some ancient sky- watchers ascribed an eclipse to a large black dragon
devouring the moon.
- *4:02 a.m. Maximum Eclipse *Another tricky aspect to this eclipse.
It is not technically total, meaning that the entire moon isn't immersed in
the umbra. Although this eclipse is partial, it's almost total. Let's
look at a lovely graphic:
[image: Lunar_eclipse_chart_close-2021Nov19 (1).png]
Almost all of the moon will pass into Earth's umbra during the November
19th event. However, a small southern sliver won't. This partial eclipse
will therefore look very much like a total lunar eclipse.
- *5:47 a.m. Umbral Eclipse ends *After the moon reaches the maximum
eclipse it will begin the slow move out of the umbra. At 5;47 a.m. the
moon will only be immersed in the penumbra. As a penumbral eclipse hardly
obscures the moon at all, the visual part of this eclipse is over.
- *6:50 a.m. Moon set *Those observers who actually want to see the
penumbral eclipse will have 1 hour and 3 minutes to do so.
- *7:03 a.m. Penumbral Eclipse ends. *Nothing to see here. Of
course, at this phase, there wasn't much to see, anyway.
*QUESTION: WHERE IN THE SKY WILL WE FIND THE MOON DURING THIS ECLIPSE?*
Considering that the eclipse begins after midnight, the moon will be high
in the western sky at the event's start and will descend toward the western
horizon during the entire eclipse.
*QUESTION: I HEARD THIS WILL BE THE LONGEST PARTIAL LUNAR ECLIPSE IN A
LONG TIME? HOW LONG?*
This partial lunar eclipse will last 3 hours, 28 minutes and 4 seconds:
longer than any other partial lunar eclipse since the one which occurred on
February 18, 1440, the same month when the Prussian confederation was
formed. The next partial lunar eclipse that is longer won't occur until
February 8, 2669! (Tell us that's not the coolest fact you've heard this
hour!)
*QUESTION: WHY IS THIS ECLIPSE SO LONG?*
Principally because the moon will be close to apogee, the point of
greatest distance from Earth. (The moon reaches apogee on November 21st.)
When at apogee, the moon is smaller and, more importantly, moving more
slowly along its orbit and so requires more time to move through the
shadow.
*QUESTION: WHY DON'T LUNAR ECLIPSES HAPPEN EACH MONTH?*
A lunar eclipse occurs when the full moon moves through Earth's shadow.
Generally when the moon is full, it passes either north or south of the
Earth-Sun line, a plane called the *ecliptic, *because the moon's orbit is
inclined relative to the ecliptic by about five degrees. If the moon's
orbit were perfectly aligned with the ecliptic, lunar eclipses would be
monthly occurrences and we wouldn't be hyping the event beyond all decency
and proportion.
[image: moons_1_wk1_fig027.jpg]
*I don't really want to wake up at 2 am to start watching this eclipse.
When is the next one and will it occur at a decent hour?*
Well, if you're not inclined to pull yourself out of bed for the November
eclipse, you'll only have to wait six months for the next one. We will
be able to see all of the total lunar eclipse that will start on the
evening of May 15th and end on May 16th. The umbral eclipse will begin at
10:27 p.m. Totality (when the moon is completely immersed in the umbra)
will start at 11:29 p.m. Totality ends at 12:53 a.m. and the umbral phase
concludes at 1:55 a.m. Whether or not this time is decent depends on
your outlook, I suppose. And, yes, weather permitting, the
planetarium will be open for the May 2022 lunar eclipse event!
Tomorrow, well, we'll wander into another space-time niche, as is our wont.
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