First published November 16, 2021.
On the night of 18 to 19 November 2021, skywatchers across North America and much of the Pacific saw a remarkably long lunar eclipse. It was a partial eclipse, not a total one, but it came very close: at its peak about 97 percent of the Moon's face sat inside Earth's darkest shadow. Its partial phase lasted 3 hours and 28 minutes, the longest partial lunar eclipse since 1440, which is why it was widely billed as the longest eclipse of the century.
Here is when it happened, who could see it, why the Moon turned a coppery red, and the meteor shower that shared the same week.
Timings and duration
The key moments, in Universal Time on 19 November 2021, were:
- Partial eclipse begins: 07:18 UTC
- Maximum eclipse: 09:03 UTC, with a magnitude of 0.974
- Partial eclipse ends: 10:47 UTC
For viewers in the eastern United States, the partial phase began at about 2:18 a.m. EST, peaked a little after 4 a.m. and ended before dawn. On the West Coast, it started around 11:18 p.m. PST on 18 November and reached maximum shortly after 1 a.m. The fainter penumbral stages, when the Moon only dims slightly, added extra time before and after, but most people notice only the partial phase.
Duration figures can be confusing because eclipses have several stages. The 3 h 28 min figure refers specifically to the time the Moon spent partly inside the umbra, Earth's dark central shadow.
Where the eclipse could be seen
A lunar eclipse is visible from anywhere on Earth where the Moon is above the horizon at the time. In November 2021 that favoured North America, which could watch the whole event in a dark night sky. Parts of South America, Australia, New Zealand, eastern Asia and the Pacific also saw some or all of it, while Europe and West Africa caught only the early stages as the Moon set.
No special equipment was needed. Unlike a solar eclipse, a lunar eclipse is completely safe to look at with the naked eye, binoculars or a telescope. A camera on a tripod, with a few test shots at different exposures, was enough to capture the colour change.
Why the Moon turns red
A lunar eclipse happens when the Sun, Earth and Moon line up, with Earth in the middle. Our planet blocks direct sunlight from reaching the Moon. But the Moon does not usually vanish, because some sunlight bends through Earth's atmosphere on its way past.
As that light travels through the air, blue wavelengths are scattered away, the same process that makes the daytime sky blue. Mostly red and orange light gets through and falls on the Moon. In effect, the Moon is lit by the glow of every sunrise and sunset happening around Earth at that moment. This is why eclipsed Moons are popularly called "blood moons."
In November 2021, because a thin sliver of the Moon stayed outside the umbra, that edge remained bright white while most of the disc took on a reddish or brownish tint. The exact shade depends on how much dust, cloud and volcanic haze is in Earth's atmosphere, so no two eclipses look quite the same.
How rare was it really?
Calling it the longest eclipse of the century needs a small footnote. Total lunar eclipses can have longer overall durations from start to finish, and the July 2018 total eclipse had the longest totality of the 21st century. What made November 2021 special was its length as a partial eclipse. Because the Moon passed so close to, but not fully into, the umbra, it lingered in partial shadow for an unusually long time.
Lunar eclipses in general are not rare: somewhere on Earth there are usually two or more a year. The next total lunar eclipse after this event came in May 2022.
The Leonid meteor shower that same week
The eclipse arrived just after the peak of the Leonids, one of the best-known annual meteor showers. In 2021 the Leonids peaked around Wednesday 17 November, though the shower runs from early November to early December.
The meteors are tiny pieces of debris shed by comet 55P/Tempel-Tuttle. The comet does not circle Earth, as is sometimes claimed; it orbits the Sun roughly every 33 years, leaving trails of dust along its path. Each November Earth crosses those trails, and the grains burn up as streaks of light high in the atmosphere. Because the streaks appear to come from the direction of the constellation Leo, the shower is named after it.
In an ordinary year the Leonids produce around 15 meteors an hour under dark skies. Every 33 years or so, when the comet has recently passed, they can turn into spectacular storms, as in 1833 and 1966, when observers saw thousands per hour or more.
In 2021 conditions were not ideal. The Moon was almost full that week, and its glare washed out all but the brightest meteors. Watching after moonset, or with the Moon behind a building or tree, gave the best chance.
Tips for future eclipses and meteor showers
- Check a dated timetable for your location. Sites such as Time and Date show exactly which stages are visible from your town and at what local time.
- Look at the weather, not just the calendar. Cloud cover is the most common reason people miss an eclipse.
- Give your eyes time. For meteors, spend at least 20 minutes away from phone screens and bright lights.
- Use a tripod. A phone or camera held still on a tripod captures the red Moon far better than handheld shots.
The Leonids guide on the same site lists the dates for upcoming years.
Sources: Time and Date: partial lunar eclipse of 19 November 2021; Wikipedia: Leonids; Time and Date: Leonids; Good News Network.
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