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: CXXI

"Look on the bright side of life."

-Monty Python's Flying Circus

THE DAILY ASTRONOMER Monday, May 9, 2022

The May 2022 Total Lunar Eclipse

The waiting is almost over! In less than one week, we'll experience a total lunar eclipse. This soul-elevating, life-affirming spectacle occurs on the night of May 15/16th. For the benefit of those who don't spend their lives steeped in the stygian gloom, a lunar eclipse occurs when the full moon moves through Earth's shadow. We recognize a few types of lunar eclipse: [Refer to helpful diagram below]

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.

During the May 15th eclipse, the moon will move entirely through Earth's umbra. The moon will also pass into and then out of the penumbra before and after the total eclipse, respectively. Now, for the all-important time-line. [Eastern Daylight Time]

May 15 - 9:32 p.m. PENUMBRAL ECLIPSE BEGINS

The penumbral eclipse begins when Earth first touches the penumbra. The moon passes completely into the penumbra before it reaches the umbra. Honestly, unless you're one of those mystical poetic types who can actually tell the difference between a whisper of a breeze and a caressing zephyr, you won't notice much during the penumbral part of a lunar eclipse. Perhaps the brilliant moon's pallor is rendered a few phantoms less vibrant, but even that is a stretch.

May 15 - 10:27 p.m. PARTIAL ECLIPSE BEGINS

This is when the 'action' starts. The umbra is the dark interior shadow. Once the umbral eclipse begins, we'll see Earth's curved shadow against the moon. We'll watch the shadow migrate across the moon until the moon is completely immersed in Earth's shadow.

May 15 - 11:29 p.m. TOTALITY BEGINS

Totality begins when the moon is completed inside Earth's umbra. The moon will not be wholly lost from sight. Instead it will appear reddish, because Earth's atmosphere scatters blue light, but directs red light into its shadow. (We see a blue sky during the sky because of this effect.) The eclipsed moon will reflect this reddish light back to us, producing the ominously named 'blood' moon. One effect that we think is absolutely magnificent is the 'spherical moon' phenomenon. During totality, the color differential across the moon's facade lends it a spherical appearance. The moon actually appears as a crimson sphere in space, as opposed to the full moon's usual disc-like appearance.

May 16 - 12:11 a.m. MAXIMUM ECLIPSE

When the distance separating the center of the shadow and the moon's center is at a minimum.

May 16 - 12:53 a.m. TOTALITY ENDS

At this moment, the moon starts its exit from the umbra. We will see a thin sliver of the moon emerging from the inner shadow.

May 16 - 1:55 a.m. UMBRAL ECLIPSE ENDS

For all intents and purposes, the show is now over. The moon completely leaves the umbra and appears, well, like a full moon again, except that it remains immersed in the penumbra.

May 16 - 2:50 a.m. PENUMBRAL ECLIPSE ENDS

The eclipse event is now technically over. Of course, the moon's brightness is hardly diminished during this last hour because the penumbra is so faint.

320px-Lunar_eclipse_chart_close-2022may16 (1).png

The moon's path through Earth's shadow. The progression is from right to left.

Now, for some Q and A

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.

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.

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.

0 Extremely dark eclipse. The moon is almost invisible during totality.
1 Grey/brown eclipse. Moon's features 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.

WILL THE SOUTHWORTH PLANETARIUM BE OPEN FOR THIS ECLIPSE. IF SO, WHEN WILL YOU OPEN AND CLOSE?

Weather permitting, of course, the planetarium will be open for the total lunar eclipse. We will open at 10:00 p.m. At 10:15 p.m. we'll present a brief show about the lunar eclipse in our star dome theater. At 10:25 p.m., a couple of minutes prior to the moon's first contact with the umbra (inner shadow), we'll gather outside to observe the eclipse. We will close at 1:00 a.m., just after the end of totality. It has been our experience that the vast majority of people lose interest once the moon starts leaving the umbra. Again, if the sky is overcast, we will not open. Note: the penumbral eclipse will be in progress during our star dome presentation. However, the penumbral phase of the eclipse isn't truly noticeable.

EVERY LUNAR ECLIPSE IS ASSOCIATED WITH A SOLAR ECLIPSE THAT OCCURS EITHER AFTER OR BEFORE IT. WHEN WILL THAT ECLIPSE HAPPEN AND WILL WE SEE ANY OF IT?

A partial solar eclipse occurred April 30th. Unfortunately, it was only visible in the southern hemisphere: South America and Antarctica.

WILL ANY OTHER LUNAR ECLIPSE OCCUR THIS YEAR? IF SO, WILL WE SEE IT?

Yes, another total lunar eclipse will occur on November 8, 2022. We will see the first half of this eclipse. Totality begins at 5:16 a.m. and ends at 6:41 a.m. However, in Portland, the moon will set at 6:32 a.m. Although the moon shall remain above the horizon for most of the totality period, it will be exceedingly difficult to see owing to its low position along the horizon. And, in anticipation of the question, no we likely won't be open for that event.

WILL ECLIPSES EVER STOP BECAUSE OF THE MOON'S RECESSION FROM EARTH?

The moon is moving away from Earth at the rate of 3 -4 cm per year. However, Earth's shadow extends about 840,000 miles into space and the moon's distance from Earth, which currently can't exceed about 252,000 miles, will only increase to about 325,000 miles by the time the Sun expands into the red giant stage. Consequently, lunar eclipses will continue as long as the Sun continues to shine. Total solar eclipses will eventually stop...in about 600 million years.

*I realize that describing any celestial event as unexciting is as blasphemous to some as a New Englander declaring that "football is only a game." So, my apologies to those select few who think that all things cosmic, from the occultation of star UCAC4 273-201720 by asteroid 4828 Misenus -which also happens on May 15th- to the discovery that our Universe is wholly encapsulated in a small bog bubble, should engender a sense of unconstrained ecstasy.

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