May's full moon, known as the Flower Moon, will be a "supermoon" as the lunar phase coincides with our satellite's closest approach to Earth. It also coincides with the only total lunar eclipse of the year, earning it the moniker "Super Flower Blood Moon." So, skywatchers who miss out on the lunar eclipse can still enjoy the full moon glowing slightly bigger and brighter than normal in the night sky.
The moon will be full on Wednesday (May 26) at 7:14 a.m. EDT (1114 GMT), according to NASA. For observers on the U.S. East Coast, the moon will be below the horizon at that point — the moon sets at 5:33 a.m. local time in New York City, for example. Moonrise in New York is at 8:53 p.m. the evening of May 26 and moonset is the next morning at 6:20 a.m., according to Time and Date. The sun sets the evening of May 26 at 8:16 p.m. local time.
Biggest supermoon of 2021
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The moon becomes full less than 10 hours after reaching perigee, the nearest point to Earth in its elliptical orbit. When it is closer to Earth, the full moon can appear up to 14% larger and 30% brighter than an average full moon — a phenomenon popularly known as a supermoon.
On average, the angular diameter of the moon is about 31 arcminutes — a touch more than one-half degree. One degree is about the size of a pinky finger held at arm's length. During Wednesday's supermoon the moon will be about 33.4 arcminutes wide, or about 10% larger in diameter. One degree is equal to 60 arcminutes, so it will take a very observant skywatcher to notice the difference.
When the moon reaches perigee on Tuesday (May 25) at 9:21 p.m. EDT (0121 May 26 GMT), it will be 222,022 miles (357,311 kilometers) from Earth, according to Heavens-Above.com calculations. On average the moon is 240,000 miles (384,400 km) from Earth. When the full moon and perigee are close, it is commonly called a supermoon.
However, because "supermoon" is not an astronomical term with a scientific definition, the term is not consistently used in the same way. Whether a moon qualifies as "super" depends on how closely its perigee and full phase coincide, and exactly how close those events need to be remains up for debate.
Some say the Super Flower Blood Moon is only the second supermoon of 2021, with April's Super Pink Moon being the first. But by looser definitions, the Full Worm Moon of March also qualified as a supermoon, making the Flower Moon the third and final supermoon of the year.
Observing the "blood moon"
Full moons occur when the moon is exactly on the opposite side of the Earth from the sun. Most of the time the moon is illuminated by the sun's light, but occasionally the moon's orbit carries it within the shadow of the Earth, producing a lunar eclipse.
Much of the world will see a total lunar eclipse, or "blood moon" with this full moon, with the best views over southeast Asia, Australia, New Zealand and the Pacific. The umbral phase of the eclipse — the point where the moon darkens completely and turns reddish in Earth's darker, inner shadow — won't be visible from the eastern part of the U.S., and the moon will set before the eclipse ends for observers on the U.S. West Coast.
The latter half of the eclipse will be visible if you live west of the Mississippi, where the total phase will start just before the moon sets. Observers on the East Coast north of Washington will only catch the start of the penumbral phase before the moon sets in the morning; the moon will look slightly darker and a bit discolored. Some people describe it as looking a bit brown, or tea-stained.
From points south of Washington and west of Pennsylvania, the moon will be partially eclipsed as it sets in the morning, appearing to have a dark "bite" taken out of it. Exactly how much of the partial phase is visible depends on your location. (Time and Date has an interactive map where you can enter your location.)
For those who don't get to see the eclipse, the moon still offers bright views through binoculars or a small telescope. If anything the full moon appears so bright it can be hard to see details because there are no shadows to give any contrast.
From a lunar observer's perspective, a full moon means the sun is directly overhead — it would be noontime on the moon. Moon filters are available that can make some features stand out, but waiting a few days after the full moon or observing a few days before, shadows bring out more craters and other details.
Planets, stars and constellations
While Earth's shadow is obscuring the moon's bright glare during the eclipse, stars and planets will be easier to spot in the night sky. Being in the constellation Scorpius, the scorpion, the moon will be to the northwest of Antares, the brightest star in the constellation. Antares is recognizable because of its distinct orange-red color.
On Saturday (May 29), three days after the full moon, the planets Mercury and Venus will be in conjunction, or sharing the same celestial longitude — Venus will be directly north of Mercury, and will pass within a quarter of a degree of the smaller planet. The actual moment of conjunction takes place at 1:34 a.m. EDT (0534 GMT), so it won't be visible from the U.S., but the planets will still be quite close to each other in the evening sky.
Venus is so bright that it is often one of the first objects (besides the moon) to become visible in the evening. In New York City the sun sets at 8:18 p.m. on May 29, and as the sky darkens one can see how soon Venus becomes visible — at sunset the planet will be 13 degrees above the horizon. About a half-hour after sunset it will be only 7-8 degrees, so the two planets will be challenging to see unless one has a relatively clear western horizon. That said, once you see them they will be close enough together that through binoculars they will be in the same field of view.
On the night of the full moon (May 26) Venus will be at about the same altitude at sunset, Mercury, meanwhile, will be higher in the sky (about 14 degrees). Both planets will be in the constellation Taurus, the bull.
Also visible Wednesday night (May 26) is Mars, which from mid-northern latitudes will be about 35 degrees above the western horizon at sunset, in the constellation Gemini, the twins. The Red Planet sets in New York at 11:32 p.m. local time.
Saturn and Jupiter rise after midnight, at 12:42 a.m. and 1:31 a.m. on May 27 in New York, respectively. By sunrise, both are about 33 degrees high in the southeast. Saturn will be in the constellation Capricornus, the sea goat and Jupiter will be in Aquarius, the water bearer. As both constellations are relatively faint, from urban and suburban locations Jupiter and Saturn will be the brightest "stars" in the area.
How the Flower Moon got its 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, according to the Ontario Native Literacy Coalition.
The Cree called it the 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.
Related: Full moon names (and more) for 2020
For the Chinese lunar calendar, the full moon occurs in the middle of the fourth month, Huáiyuè, or Locust Tree Month.
In the Southern Hemisphere, 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.
Among the Aboriginal Yolgnu people of Australia, living near the coast, kept close track of the correlation between moon phases and tides. They believe the full moon becomes full of water at high tides as it rises.
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