THE SOUTHWORTH PLANETARIUM
70 Falmouth Street Portland,Maine 04103
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.
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.
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.
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:
