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: XI
"I'd rather die of passion than of boredom."
-Vincent Van Gogh
THE DAILY ASTRONOMER
Thursday, September 16, 2021
November's Micromoon Eclipse Part IV: Eclipse Questions
Hot Darn, do we love questions!
No, honestly! Questions are interesting, often challenging and invariably
illuminating. Your questions are our opportunities to explore the Universe
in greater depth. Also, they give us opportunities to talk. So, please keep
those cards and letters coming. Today's article features lunar eclipse
questions we've been asked and the responses we've offered...not verbatim,
of course.
*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.
*Total solar eclipses are predicted to end in about 600 million years due
to the moon's motion away from Earth. When will lunar eclipses end?*
Lunar eclipses will never end. Or, to be a bit more temporally correct,
lunar eclipses will continue until the Sun's life cycle ends. While the
moon does recede from Earth at the current rate of 4 centimeter/year, it
will never move so far away as to be beyond Earth's shadow.
[image: skills102-7.gif]
Earth's shadow cone extends approximately 840,000 miles into space.
Presently, the moon doesn't veer farther from our planet than about 252,000
miles. In approximately five billion years, at the time when the Sun
evolves into the red giant stage, its orbit will be forty percent larger
than it is today. Its apogee distance will then approximately equal
353,000 miles, still well within the shadow cone.*
*A lunar eclipse is either followed or preceded by a solar eclipse. When
is the solar eclipse that is associated with this lunar eclipse? Will we
see it here?*
Yes, a total solar eclipse will follow this lunar eclipse. No, we won't
see it here. A total solar eclipse will occur on December 4th and will be
visible in the southernmost regions of the southern hemisphere. The
totality path, the only region in which the total solar eclipse will be
visible, will sweep across parts of Antarctica. Perhaps the late spring
weather will enable more people than usual to observe the event in that
frigid and remote location.
*Why do eclipsed moons often appear red?*
Simply because Earth's shadow cone is steeped in red light. Realize
that the shadow's cone's base is encircled by regions on Earth where the
sun is either rising or setting. We know that the skies tend to be
reddened around this time. Some of that light is directed into the shadow
cone. When the full moon moves into Earth's shadow, that red light is
reflected back to us, making the moon appear reddish. We should note
that not all eclipsed moons appear red. Some are darker and some will
appear orangish, depending on the atmospheric conditions. The Danjon
scale lists the various eclipse colors:
- *0 * Very dark eclipse. Moon might even not be visible during
totality.
- *1 * Brown or grey coloration.
- *2 * Rust-colored eclipse. Also deep red. Distinct color
differential, with the central moon dark and the outer edge brighter and
more colorful.
- *3 *Brick red eclipse. Yellowish rim around umbral shadow
- *4 * Very bright eclipse. Copper red or orange eclipse.
Umbral shadow has a bluish edge
*I've seen a few lunar eclipses, but have never seen a solar eclipse. Are
lunar eclipses much more common?*
No, not at all. If one takes penumbral eclipses into account, lunar
eclipses are slightly more common than solar eclipses. However, the
frequency difference isn't substantial. Lunar eclipses seem to be more
common because many more people have seen a lunar eclipse than a solar
eclipse. Why? Well, a lunar eclipse will be visible in all locations
where the moon is above the horizon during the eclipse. Conversely, a
total solar eclipse is only visible along a narrow strip of land
called the *totality
path*.
[image: media_101_101cf433-49fb-4b40-b647-0a2923321fef_php8DWLei.png]
The moon's shadow tapers down to a small area once it reaches Earth. Only
observers within the path of land across which this shadow passes will see
a total solar eclipse.
[image: WEB11715-2010_640.jpg]
However, observers is all the regions where the moon appears above the
horizon during an eclipse will see the eclipse because our planet is the
shadow-casting body.
*Why did you tell us about this event so early and why did you devote an
entire week to it?*
I have been accused -rightly- of sometimes not providing sufficient notice
to subscribers about important astronomical events. Hence, the early
alert for this astronomical event. Lunar eclipses are among the most
wondrously beautiful of all celestial spectacles, and, heavens above,
that's saying something!
*The Sun's expansion will likely destroy the moon. According to models, the
Sun's tenuous outer atmosphere could extend as far as Earth. The
resultant drag will cause the moon's orbit to rapidly decay, causing it to
fall toward Earth. Once the moon reaches the Roche Limit, approximately
17,887 miles, the planet's tidal forces will overwhelm the moon's internal
gravity and cause it to disintegrate.
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>
|
