The full moon of May, also known as the Flower Moon, blooms today, May 29, reaching its fullest phase at 10:20 a.m. EDT (1420 GMT). While the moon is officially full during the day, the rising satellite will provide fine views by nighttime.
The online observatory Slooh, which provides live views of space from robotic telescopes, will host a webcast showcasing tonight's full moon. Read more: See the Full Flower Moon of May 2018 in a Slooh Webcast Tonight!
On the evening of the full moon, the moon will rise just a few minutes after sunset at 8:22 p.m. local time in New York City, according to timeanddate.com. Most people won't notice the difference between the moment when it is officially full and its appearance the night before or after.
Since the moon is in the late spring sky, it will appear in the east-southeast for Northern Hemisphere observers. That's because the moon's path as seen from Earth roughly follows the ecliptic, the plane of the Earth's orbit around the sun. The part of the ecliptic the moon is in is below the celestial equator (Earth's equator projected onto the sky), so as the moon rises, it's a bit south of due east. [The Moon: 10 Surprising Lunar Facts]
Observers who live farther east will be able to see the moon become officially full, since it will be above the horizon — though those skywatchers would have to be in cities that are at least as far east as New Delhi, where the moon rises at 7 p.m. and becomes full at 7:50 p.m. local time.
For skywatchers in Europe, Africa, the Middle East, North America and South America, the moon won't be above the horizon when it reaches peak fullness. However, viewers in Hawaii and the west side of Alaska can catch a glimpse of the full moon just before it sets early in the morning. (You can find out what time the moon will be visible at your location with this moonrise and moonset calculator.)
The reason much of the world can't see the full moon is that the lunar phase is defined as the moment the moon is on exactly the opposite side of Earth from the sun. Because the exact timing depends on where the moon is in its orbit around Earth, the full moon is below the horizon for about half of the world. The moon's orbit also is not a perfect circle — it's a tiny bit elliptical.
Other skywatching treats
The full moon has a tendency to drown out other objects in the night sky, since it is so bright (magnitude minus 12.6) that it can cast visible shadows. The brightness isn't always apparent from big city locations, though, because of the competition from streetlamps, neon signs and other sources of light pollution.
On May 29, the full moon will share the sky with some of the planets that are viewable with the naked eye. Venus, for example, will set at about 10:53 p.m. in New York on May 29, and as the moon rises, it will be a full 26 degrees above the horizon, according to heavens-above.com calculations. Observers will see Venus in the western sky and the moon nearly opposite in the east.
People in the Southern Hemisphere will also get views of Venus on that night, though Venus is lower in the sky than in the Northern Hemisphere. In Sydney, Venus will be about 20.4 degrees above the horizon at sunset, which is at 4:55 p.m. local time on May 29. The planet sets at 7:06 p.m.
As the sky gets darker, one can see Jupiter, which rises in the constellation Libra before sunset at 6:15 p.m. local time in New York. The planet will be some distance west of the moon, looking as though it is leading the moon across the sky. Jupiter reached opposition — its closest approach to Earth — on May 9, but at the end of the month, it will still be well-placed for observation almost all night.
In Sydney Jupiter rises in the midafternoon, at 3:40 p.m. The planet will be quite high in the sky as the evening progresses, getting as high as 71 degrees at its highest. The planet sets at 5:02 a.m. local time the morning of the May 30.
Following moonrise (just as Venus sets in the west), Saturn will rise in the constellation Sagittarius at 10:21 p.m. local time in New York City, reaching its highest point in the sky, called the meridian transit, at 2:58 on the morning of May 30. It will be high enough (some 26.9 degrees above the horizon) to see relatively easily, and it'll be bright enough that even city dwellers can see it glow with a clear, whitish-yellow light. Saturn's rings are visible in even a small telescope or large binoculars.
The ringed planet is visible for much more of the night in Australia. For observers in Sydney Saturn rises at 6:57 p.m. local time on May 29 and sets at 9:02 a.m. the morning of May 30. Like Jupiter it will be high in the sky, reaching 78.5 degrees at about 1:59 a.m. on May 30.
Mars rises just after midnight at 12:17 a.m. on May 30. It is in the constellation Capricorn, and by 4:56 a.m., it will be 27 degrees above the horizon, its highest point for the night. It, too, is bright, and its red color makes it easily discernable.
For eastern Australia, Mars comes up around 9 p.m. local time. Like Jupiter and Saturn, it will be very high in the sky; it reaches nearly 78 degrees when it crosses the meridian, the highest point, at about 3:56 a.m. the morning of May 30.
Planets are easy targets for citybound skywatchers, but a quick trip to a suburb or the countryside can serve up darker skies that offer more to see – though, as noted, the full moon will make seeing fainter objects harder. That said, in May, the traditional winter constellations make way for those of summer.
Gemini, a prominent constellation for Northern Hemisphere observers in the winter (and the constellation where you'll find Venus), sets in the late evening, marked by its brightest stars, Castor and Pollux. Located some 51 light-years away from Earth, Castor is actually a group of six stars that are so close together that they look like a single star. Using a small, amateur telescope, you can see the star as a binary, and a larger one can resolve a third star in the group. (The others can only be seen with a spectroscope.)
Following the zodiac eastward, one can see the constellations Leo (the Lion) and Virgo. The constellation Libra follows Virgo, though on a full-moon night, only a few of the stars in this constellation will be visible, since most are relatively faint.
By 10 p.m. New York time, the Summer Triangle, made up of the stars Altair, Vega and Deneb, will clear the horizon. As its name implies, the Summer Triangle is mostly visible in the warmer months for viewers in the Northern Hemisphere. Like the Big Dipper, it is an asterism (a recognizable star pattern) rather than a constellation (a region in the sky) and can be used for celestial navigation. The three stars make a triangle, with the shortest side linking Deneb and Vega, and if one imagines Altair at the tip, it makes a shape that always points south. (For Southern Hemisphere observers, it points roughly north). Deneb is in the constellation Cygnus the swan, and it also shares its portion of the sky with the Milky Way, which is almost invisible to observers in cities.
The Milky Way is made of stars too numerous to see as individual objects and shows where the plane of our galaxy is. If one follows the Milky Way from Cygnus, one reaches Cassiopeia, a "W" shape that points up in the premidnight hours. Cassiopeia is one of the constellations that never sets in the northern U.S. It is almost directly on the opposite side of Polaris, the pole star, from the Big Dipper — an asterism in the constellation of Ursa Major, the Great Bear – making it a useful way to find Polaris if the Dipper isn't visible.
How the Flower Moon got its name
The May full moon has some evocative names. The Old Farmer's Almanac calls it the Flower Moon, which is similar to what many Algonquin-speaking peoples in what is now the northeastern U.S. called it. Other native people had different names for it, though. According to the Ontario Native Literacy Coalition, the Cree in Montana and Canada called it a Frog Moon, since that was the time of year when the amphibians became active.
Chinese lunar calendars say May's full moon falls in the fourth month, called Huáiyuè, the Locust Tree month, for when the eponymous trees blossom. [Full Moon Names 2018: From Wolf Moons to Cold Moons]
Jewish and Muslim lunar calendars both begin their months near the time of the new moon, which happened on May 15. This month's full moon falls in the middle of the Hebrew month of Sivan. For observant Muslims, the month of Ramadan begins on May 16 (just after the new moon), and during that time, they fast from sunrise to sunset. May's full moon will mark the halfway point of the holiday.
In the Southern Hemisphere, names for full moons were associated with the coming of winter rather than summer. The Māori, for example, provided the following description for the lunar month of Pipiri, which occurred from May to June: "all things on earth are contracted because of the cold," according to the Encyclopedia of New Zealand.
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