May's full moon, known as the Flower Moon, will undergo an eclipse on the night of May 15-16, which will be visible in the Americas, Europe, Africa, the Middle East, the eastern Pacific and the South Pacific as far west as New Zealand.
For New York City observers, the full moon will happen at 12:14 a.m. on May 16 (0414 UTC) according to the U.S. Naval Observatory. At that point the eclipse will be well underway; the eclipse starts on the evening of May 15 at 9:32 p.m. local time. By the time the moon is officially full, the eclipse will be near maximum (which occurs at 12:11 a.m.).
Full moons happen when the Moon is on the opposite side of the Earth from the sun, so the timing of moon phases depends on one's time zone. Since the Earth is directly between the sun and moon, one might expect that the moon would enter the Earth's shadow every 28.5 days (this is the time it takes the moon to make a circuit of the Earth). That doesn't happen, because the moon's orbit is tilted slightly – about 5 degrees – to the plane of the Earth's orbit, so most of the time the moon "misses" the shadow of the Earth and we see a full moon.
Related: How to photograph a lunar eclipse
Flower Moon lunar eclipse
This full moon will be different – the moon will enter the Earth's shadow and people on the night side of the Earth will see a total lunar eclipse. The timing isn't just accidental – in April, there was a partial solar eclipse, and lunar and solar eclipses occurred together. The April eclipse was approximately two weeks – one half a lunar orbit – before the lunar eclipse.
Lunar and solar eclipses happen close to each other because for an eclipse to happen at all, the moon needs to be at one of the points in its orbit where it crosses the plane of Earth's orbit. These points are called nodes. When the nodes are in line with the Earth, moon and sun, the moon will cross in front of the sun (when it would be a new moon) and passes through the Earth's shadow (when it would be a full moon).
A lunar eclipse has several phases. The first and last is the penumbral eclipse when the moon is in the penumbra, the lighter part of the Earth's shadow. Looking at the moon there isn't any obvious difference – it gets a little darker, and some people say it looks a little more yellow or brownish than usual, but there's no dark shadow line. The next phase is called the partial eclipse when the moon enters the dark part of the Earth's shadow; this is also called the umbral phase. During the middle of the eclipse, we get totality, when the moon is completely inside the umbra and turns a characteristic red.
Observing the Flower Moon eclipse
In New York, the penumbral phase starts May 15 at 9:32 p.m. Eastern Time. The umbral phase begins at 10:27 p.m., and the eclipse reaches totality at 11:29 p.m. At that point, the moon will be about 26 degrees above the southeastern horizon. Totality ends at 12:53 a.m. May 16, and the moon passes out of the umbra at 1:55 a.m. The penumbral phase (and the eclipse) ends at 2:50 a.m.
Observers in the Eastern and Central time zones of North America will see the eclipse from start to finish – the moon rises in New York City well before the eclipse begins, at 6:29 p.m. on May 15. In Miami, which is in the same time zone, the moon rises at 6:50 p.m. and the eclipse also starts at 9:32 p.m.
In South America, Colombia, Ecuador, Peru, Panama and far western Brazil do not observe daylight savings, so the times to see the lunar eclipse there will be the same as Central Time in the U.S. For example in Bogota, Colombia, the eclipse begins at 8:32 p.m. local time and totality begins at 10:29 p.m. South American observers will see the moon higher in the sky than their North American counterparts, however. In Bogota, the moon will be 58 degrees high when totality starts. In Lima, Peru, the moon will be 66 degrees high just south of east.
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Further South, in Santiago, Chile, the eclipse begins at 9:32 p.m. with the moon just north of east at an altitude of 46 degrees, halfway to the zenith. When totality begins the moon will be a full 69 degrees high in the northeast.
In the western United States, the total phase of the eclipse will be visible – in Los Angeles, for example, it starts at 8:29 p.m. Pacific Daylight Time, well after moonrise at 7:40 p.m. But as one moves north and west the eclipse moves closer to moonrise. In Seattle, the total phase starts at 8:29 p.m. but the moon doesn't rise until 8:34 p.m. Maximum eclipse is at 9:11 p.m., with the moon only 4 degrees high in the southeast, so Seattleites will see a rising, blood-red moon.
Moving eastwards. Observers in London will see the eclipse begin but the end will be after moonset on May 16. The partial phase of the eclipse starts at 3:27 a.m. local time, and the total phase at 4:29 a.m. Maximum eclipse is at 5:06 a.m., and the moon sets in the southwest just 4 minutes later. In Paris the situation is similar with the local times an hour later – maximum eclipse is at 6:06 a.m., and the moon sets at 6:10 a.m.
Blood moon effect
The "blood moon" effect at totality is due to the atmosphere of the Earth. If one were standing on the moon one would see a total solar eclipse, and the Earth would cover the sun entirely (from the moon the Earth would appear four times as wide as the moon from Earth). The edge of the Earth, however, would appear a bright red-orange.
Earth's atmosphere refracts and absorbs light from the sun. That means the sunlight bends around the Earth as it does in a lens. The Earth's atmosphere also absorbs and scatters shorter wavelengths in the blue and green parts of the spectrum, so the light that gets to the moon is preferentially reddish.
As the moon will be dimmed when it is in eclipse, it will be easier to see the constellations the moon is in – in this case, the moon will be in Libra, which is usually washed out by the full moon's light.
For those that don't get to see the eclipse, there is still a line of planets to be seen in the east just before dawn. In mid-northern latitudes, by about 3:30 a.m. one will see Venus, Jupiter, Mars and Saturn forming a diagonal line from the east to southeast. Venus and Jupiter will be in the constellation Pisces, and Mars in Aquarius. From Tokyo, where the lunar eclipse won't be visible, Saturn rises at 12:39 a.m. local time, in the constellation Capricorn. Mars follows at 1:56 a.m., Jupiter at 2:14 a.m. and Venus at 2:52 a.m. Venus at 3:30 a.m. will be about 8 degrees above the eastern horizon, and Saturn at 29 degrees in the southeast.
In the Southern Hemisphere, the planets will appear to make a more vertical line with respect to the horizon and be higher in the sky. From Sydney, Australia, Saturn rises at 11:32 p.m. local time on May 15, Mars follows at 1:46 a.m. May 16, Jupiter at 2:23 a.m. and Venus at 3:29 a.m. By about 4:30 a.m. Venus is 12 degrees high and Saturn is at 60 degrees. The line the four planets make will run from the east to northeast.
How the Flower Moon got it's name
The full moon of May is often called a flower moon, and the term comes from the blooms that appear in North America around that time; Algonquin-speaking peoples in the northeastern part of the continent such as the Ojibwe (or Anishinaabe), called it something similar (Waawaaskone Giizis, which means "flower moon" according to the Ontario Native Literacy Coalition). The Cree called it Athikipisim, or Frog Moon, as May is when frogs tend to become active. Both Anishinaabe and Cree traditions reflect the environment in northeastern North America, where the two peoples live.
In the Chinese lunar calendar, the full moon is the middle of the fourth month, Huáiyuè, or Locust Tree Month.
The Māori described the lunar month of Pipiri, which occurs from May to June: "all things on earth are contracted because of the cold," according to the Encyclopedia of New Zealand – May in the Southern Hemisphere is approaching winter.
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