THE SOUTHWORTH PLANETARIUM
70 Falmouth Street      Portland, Maine 04103
(207) 780-4249      usm.maine.edu/planet
43.6667° N    70.2667° W 
Founded January 1970
2022-2023: XXXV
Sunrise: 7:21 a.m.
Sunset: 4:24 p.m.
Civil twilight ends: 4;54 p.m.
Sun's host constellation: Libra the Scales
Moon phase: Full
Moonrise: 4:04 p.m.
Moonset: 6:32 a.m.
Julian date: 2459890.21
"Don't vote. It only encourages them." -Seen on a bumper sticker (and also attributed to many individuals)


THE DAILY ASTRONOMER
Monday, November 7, 2022
Questions About Tomorrow Morning's Total Lunar Eclipse


Have you set your alarm clocks for 4 a.m?
If not, we strongly encourage you to do so if you are inclined to observe tomorrow's morning total lunar eclipse. This type of eclipse occurs when the full moon moves directly through Earth's inner shadow, called the umbra. Although we'll only see the first phases (the moon sets during totality), watching this spectacle is certainly worth the sleep deprivation. After all, lunar eclipses don't occur every single month. (Find out why below)

As is our wont, we will adopt the question/answer format when discussing impending celestial events.

WHEN WILL IT OCCUR AND WHAT IS THE TIMELINE?

PENUMBRAL ECLIPSE BEGINS - 3:02:15 a.m.
Nothing to see here. The moon first touches the penumbra, the outer part of Earth's shadow. The resultant brightness diminishment is so slight as to be unobservable. While those in possession of superhuman eyesight might be able to notice an obscuration, we mortals would just look upon a full moon as it, well, always appears.

PARTIAL ECLIPSE BEGINS - 4:09:12 a.m.
This is what you'll likely want to see: the moon first touches the umbra. Now, you can observe the curved shadow moving across the bright lunar disc. During the next hour and seven minutes, the moon will move progressively deeper into the umbra until it is completely covered.

TOTAL ECLIPSE BEGINS - 5:16:39 a.m.
Totality, the time period in which the moon is completely inside the umbra, begins.

MAXIMUM ECLIPSE - 5:59:11 a.m.
The moment when the moon passes through the deepest part of the inner shadow.

MOON SET - 6:32 a.m.
The moon sets from our perspective. Do note, however, that the moon will likely be difficult to see during most of totality, however, due to its low position along the western horizon.

We'll include the rest of the timetable for completeness:

TOTALITY ENDS - 6:41:36 a.m.
The moon starts to leave the umbra

PARTIAL ECLIPSE ENDS - 7:49:03 a.m.
The moon leaves the umbra. The scarcely visible penumbral eclipse continues

PENUMBRAL ECLIPSE ENDS - 8:56:09 a.m.
The superhumans can return to bed now.

ARE THERE DIFFERENT TYPES OF LUNAR ECLIPSES?
Yes. Tomorrow's event is a total lunar eclipse, one of four types, all of which are defined as follows.

  • Partial Penumbral: when only part of the moon's moves through the penumbra, Earth's outer shadow. Excitement rating: nada, zilch, goose egg
  • Penumbra: when the entire moon moves through the penumbra, but doesn't touch the umbra. Excitement rating: 2.3 atomic layers higher than goose egg
  • Partial: when part of the moon moves through the umbra, Earth's inner shadow Excitement rating: Much higher! Ostrich egg
  • Total: when all of the moon moves through the umbra. Excitement rating: Stratospheric!! T-Rex egg.
Earths-penumbra-and-umbra.png

WHY DON'T LUNAR ECLIPSES OCCUR EVERY MONTH?
Lunar eclipses would occur during every full moon if the moon's orbit were perfectly aligned with Earth's.   However, the moon's inclination is about 5.1 degrees. Or, its orbit subtends a 5.1 degree angle relative to our planet's orbit, called the ecliptic.  Consequently, during most oppositions (full moons), the moon is either north or south of Earth's orbital plane. As a result, the moon will not pass directly through Earth's shadow.   This month, the full moon is close enough to the node, or the intersection between the orbits, that it will travel through the shadow cone to produce a lunar eclipse.

moon.orbit_-e1498934371864.jpg

WHY DOES THE MOON TURN RED DURING A TOTAL LUNAR ECLIPSE?
Because red light originating from the ring of sunsets/sunrises fills Earth's shadow cone. The eclipsed moon reflects that red light just as the moon reflects sunlight.
Umbra_color_schematic-630x354.jpg
We should mention that not all total lunar eclipses appear the same. Variations in the atmospheric conditions cause variations in the colorations of total lunar eclipses. French astronomer André-Louis Danjon (1890-1967) proposed a scale designed to measure these variations, now called, appropriately, The Danjon Scale:

  • 0    Extremely dark eclipse.  The moon is almost invisible during totality.    
  • 1     Grey/brown eclipse.   Moon's features are discernible, but difficult to observe
  • 2    Deep red/rust colored eclipse.  Central part of the moon darker than the edges
  • 3    Brick-red eclipse.    Umbral shadow exudes a bright, sometimes yellowish hue
  • 4    Bright, copper red or even orange coloration 

While the solar cycle affects these ratings, hence Danjon's decision to develop the scale, terrestrial factors such as volcanic eruptions tend to be more important.     For instance, the lunar eclipse on December 9, 1992 rated a 0 on the Danjon scale because of the eruption of Mount Pinatubo which occurred during the spring and summer of 1991. The ratings are subjective and so vary somewhat from observer to observer. 

HOW CAN ONE USE THE SAROS CYCLE TO PREDICT FUTURE LUNAR ECLIPSES?
The Saros refers to the cycle of lunar eclipses within the same series.  Successive eclipses in a given Saros Cycle are separated by 18 years, 11 days and 8 hours.   For instance, Sunday's lunar eclipse is part of the Saros Cycle 136.    The Saros cycle duration enables us to predict with a fair degree of certainty the dates of the next few successive lunar eclipses within this cycle.          Let's try.

We assume that the next Saros 136 lunar eclipse will occur around November 18, 2040.   The actual date: November 18,2040
The date of the next Saros 136 lunar eclipse?    November 30, 2058
The following Saros 136 lunar eclipse:  December 10, 2076

The Saros Cycle duration is 18 years, 11 days and 8 HOURS, so at times, the dates between successive eclipses won't be precisely 18 days and 11 hours.Also, one cannot use this method forever as Saros Cycles are of finite duration which begin and end as a series of penumbral eclipses.   For instance, the Saros 136 lunar eclipse series began on April 13, 1680 and will end on June 1, 2960.

IF I DECIDE, WELL, IT'S JUST NOT WORTH IT TO WAKE UP EARLY, HOW LONG WILL I HAVE TO WAIT UNTIL THE NEXT ONE?
You'll only have to wait until March 14, 2025 to see the next total lunar eclipse. Fortunately, we in New England will be able to observe the entire eclipse.

WILL THE SOUTHWORTH PLANETARIUM BE OPEN FOR THIS EVENT?
Not this time. We have found that such early morning events don't attract many people. However, we intend to remain open for most of the March 14, 2025 event, weather permitting.

SPEAKING OF WHICH, WHAT IS TOMORROW MORNING'S FORECAST?
Absolutely, positively, beautifully, wonderfully and undeniably clear. You have absolutely no excuse NOT to catapult yourself out from under the covers to watch the first part of this eclipse




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