PORTLAND, Maine — On Sunday night, high in the skies over the Pine Tree State, the full moon will dim, turn blood red and fade to nearly nothing.
But don’t worry.
A little over an hour later, the familiar nighttime object will begin to brighten again. The crimson color will drain away and its normal, silver luster will return.
The impressive celestial event, known as a total lunar eclipse, is a regular occurrence but the upcoming event is the last one Mainers will be able to view, in its entirety, until 2025.
“There’s another one, later this year, but we won’t see all of it,” said Edward Gleason, director of the Southworth Planetarium on the University of Southern Maine Campus in Portland.
Gleason has been with the facility since 1999 and took his current position in 2020.
Lunar eclipses, either full or partial, occur twice a year but each is only visible to certain parts of the globe. It all depends on where the moon is in relation to a viewer’s position on Earth.
The moon produces no light of its own. The light we see coming from the moon at night is actually sunlight reflecting off it.
A full lunar eclipse takes place when our planet orbits into position between the Sun and Moon, casting a shadow on the lunar surface. In order to see the eclipse, one must be on the dark side of the world directly facing the moon.
Both the Earth and the Moon have tilted orbital planes as well, further complicating the astronomical arithmetic and geometry.
“During most full moons, we’re either above or below the Earth’s shadow cone,” Gleason said.
Full lunar eclipses are also gradual affairs. Most take more than five hours to complete. Thus, in order to see one in its entirety, the event must begin in a viewer’s location early enough to play out before the moon sinks below the horizon.
For Maine viewers, Sunday’s full moon eclipse will begin around 9:30 p.m. when the moon enters the Earth’s penumbra, or outer shadow. At that point, no visible shadow will be seen on the silver disc but it will begin to dim.
Then, an hour later, around 10:30 p.m., our planet’s visible shadow will begin to creep across the full moon, from left to right. This shadow is known as the umbra.
After another hour, around 11:30 p.m., the umbra will completely cover the moon. The moon will then continue to darken for another 40 minutes.
Around 11:10 p.m. the moon will be at its murkiest point.
But it won’t be entirely blacked out or missing. Instead, it will take on a rich red or orange color. This is why full lunar eclipses are often referred to as “blood” moons.
“The red light is sunrises and sunsets reflected from Earth,” Gleason said. “The intensity depends on particulate matter in the atmosphere.”
The moon will remain in its fully dark, cardinal-colored state until about 12:50 a.m. on Monday morning. Then, the previous course of stellar events will take place in reverse.
The umbra will exit the moon to the right at nearly 2 a.m. and the penumbra will fade by 2:50 a.m.
By 3 a.m. the full moon will be back to normal.
Unlike a solar eclipse, it is safe to view the lunar version directly. No special equipment is needed but, a small telescope or even a set of binoculars will reveal details unseen with the naked eye.
Of course, the event’s viewability from Maine is entirely weather dependent. If clouds cover the sky, the show will not go on as planned.
In that event, sky watchers can watch a livestream of the event provided by NASA.
In the fall, overnight between November 7 and 8, another lunar eclipse will take place. However, it won’t be hitting its darkest point until after the sunrise and the Moon will set below the horizon before it is over.
After November’s sky event, the next full lunar eclipse viewable in Maine — or anywhere else — won’t happen until March 14, 2025.
By then, Maine will have experienced its first total solar eclipse since 1963. Solar eclipses have a much more narrow viewing angle and western Maine will be in its path. That event, expected to draw worldwide attention to Maine, is scheduled for April 8, 2024.
“We’re already preparing for that one,” Gleason said.