Coming Sunday: A full 'SuperHarvestBlood' moon

Earth's shadow begins to fall on the moon during a total lunar eclipse, as the moon goes behind a weathervane shaped like a Spanish galleon on the Freedom Tower in Miami last Oct. 8. (Wilfredo Lee/
The Associated Press) — Earth's shadow begins to fall on the moon during a total lunar eclipse, as the moon goes behind a weathervane shaped like a Spanish galleon on the Freedom Tower in Miami last Oct. 8. (Wilfredo Lee/ The Associated Press)

Sunday night, there is going to be a “prime time” total eclipse of the moon. If the weather is clear, the timing will make it very easy to see this sky event.

A lunar eclipse occurs whenever the moon’s orbit takes all or part of the full moon into Earth’s shadow. Specifically, there are two shadows that Earth casts into space and that makes for five stages of a total lunar eclipse.

Projected from Earth’s night side into space is a dark, inner shadow cone that converges to a point beyond the moon and then spreads out again. Surrounding the outside of this dark cone is another, lighter shadow cone that continually spreads outward from Earth. This pale, expanding shadow is called the penumbra and the dark, inner cone is called the umbra.

In actuality, there is a gradual increase in the intensity of darkness from the outer edge of the penumbra to the center of the umbra.

Five Stages

For a total eclipse of the moon, the first of the five stages starts the moment the moon contacts the edge of Earth’s outer shadow. This part of the penumbra is so light that any darkening of the moon is imperceptible to the human eye. It is only when the moon is about halfway through the penumbra that we begin to notice a faint shadowing on the eastern side of the moon — its left side when looking at the lunar surface from Earth’s Northern Hemisphere.

After about a half hour, as the moon moves deeper into the penumbra, it becomes obvious that the eastern part of the lunar surface is slightly darker than its bright western side.

Stage two begins as the moon enters the dark, umbral shadow and a partial lunar eclipse begins. By this time, it is apparent that the moon looks different.

Depending on the moon’s exact path during the eclipse, it typically takes about an hour for the moon to move entirely into Earth’s umbra. At the moment the moon is completely within Earth’s dark shadow, the third stage of the eclipse starts and the total eclipse of the moon is underway.

While totality is happening, the moon usually displays a yellowish, coppery orange color that is actually due to Earth. Sunlight skimming through Earth’s atmosphere has its blue light scattered out but the yellow through red rays shine into the umbral cone and onto the moon.

An astronaut on the moon’s surface at this time would see the surrounding moonscape bathed in an eerie dark, orangish glow. Further, looking into the moon’s sky at Earth, the astronaut would see a beautiful, thin ring of brilliant orange light surrounding Earth from all the sunrises and sunsets that were taking place at that moment.

Sometimes during totality, part of the moon will remain whitish, depending on how close it is to the edge of the umbra. During the lunar eclipse Sunday, watch to see if the “bottom” of the moon stays bright since its southern rim will be near the perimeter of the umbra.

Totality usually lasts an hour or so depending on the moon’s exact path through Earth’s umbral shadow and ends as the moon begins to move out of this shadow. This moment starts stage four and the partial eclipse phases repeat in reverse order. The moon brightens across its face from east to west as it emerges from Earth’s umbra and again moves into the penumbra.

Stage five is when the moon is completely within Earth’s penumbral shadow again. About a half hour later, the shading is so weak that it is unnoticeable. Formally, the eclipse ends when the moon entirely exits the penumbra.

Celestial Coincidences

Although a total lunar eclipse is a beautiful sky event to watch in itself, there are a few celestial coincidences unique to this eclipse.

First, it is the full moon closest in time to the fall equinox, so it is also the Harvest moon. Second, just 59 minutes before mid-eclipse, the full moon reaches its closest point to Earth for the entire year. That’s called a Supermoon and this full, eclipsed moon will appear slightly larger than the other full moons this year.

Finally, although the totally eclipsed moon seldom appears as deep reddish, it can be that color when volcanic ash and aerosols are in the upper atmosphere after a major volcanic eruption. Though a significant volcanic explosion has not happened lately, recent vernacular terms the totally eclipsed moon the Blood moon.

So we might call this lunar eclipse the total eclipse of the full “SuperHarvestBlood” moon!

Timetable of the evening

The specific times for the moon to enter into and exit from Earth’s different shadows are as follows in Eastern Daylight Time for the night of Sept. 27-28.

Astronomically, the eclipse starts as the moon enters Earth’s penumbra (shadowing not visible) at 8:12 p.m. The penumbral shadowing might first be visible around 8:40. The moon then begins to enter Earth’s umbra and the first partial lunar eclipse starts at 9:07. This ends when the moon is completely within Earth’s umbra, which starts the total eclipse at 10:11.

Mid-eclipse happens at 10:47 and the total eclipse ends at 11:23 That starts the second partial eclipse, which ends at 12:27 a.m. Then the penumbra is last visible around 12:55. Finally, the moon leaves the penumbra at 1:23, formally ending the eclipse.

Museum event

The Dudley Observatory at the Museum of Innovation and Science (miSci) on Nott Terrace Heights in Schenectady will host a lunar eclipse event at the museum regardless of weather conditions. Indoors, there will be activities related to the moon for young people, and the museum’s science gallery will be open.

Outdoors, if the evening sky is clear, members of the Albany Area Amateur Astronomers will be there to observe the eclipsed moon.

Doors open at 8. There will be an admission fee for the museum gallery but the observing session and the children’s activities are free. Hope to see you there!

Richard Monda is an astronomer living in the Capital Region.