While we can't guarantee that April's showers will bring May flowers, you can definitely count on a full Flower Moon to arrive this month. In fact, the May full moon occurs tonight! See our latest update here: See the Full 'Flower Moon' Rise Tonight
The full moon of May, also known as the Flower Moon or Milk Moon, rises Wednesday (May 10) at 5:42 p.m. EDT (2142 GMT). It will appear full to the casual observer for about a day before and after. However, the exact moment at which the moon is fullest — when the sun, Earth and moon align — won't be visible to observers in North America, because the moon will be below the horizon. [The Moon: 10 Surprising Lunar Facts]
East Coast observers in the U.S., for example, will see the moon rise a few minutes before 8 p.m., 2 hours after the full moon's peak. On the other hand, if you are in Europe, the moon will reach peak fullness while it's high in the sky late at night. In Paris, for example, the full moon happens at 11:42 p.m., about 4 hours after moonrise. (You can find out what time the moon will be visible at your location with this moonrise and moonset calculator.)
The many names for May's full moon
According to the Old Farmer's Almanac, the Native American name for the May full moon was the Full Flower Moon, though some Algonquin-speaking nations named it the Corn Planting Moon or Milk Moon (though the milk in this case would likely have been referring to milkweed, not cows, which are not native to the Americas).
The Ontario Native Literacy Coalition notes that while the Ojibwe tribes of the Great Lakes area called the May full moon a Flower Moon ("Waawaaskone Giizis"), people of the Cree Nation in northern Montana and parts of Canada named it the Frog Moon because this was the time of year frogs became active.
In China, the lunar months also took on different names; in 2017 the full moon in May will be Huáiyuè (槐树月), or Locust Tree month. The Chinese weren't the only people to use a lunar calendar – lunar calendars were (and still are) common all over Asia. In the Middle East, both the Jews and Muslims used the moon as the basis for the calendar. In the Jewish tradition, months begin with the new moon, and the full moon of May will happen on the 14th day of the month of Iyar. On the Islamic calendar, May's full moon falls in the month of Sha'ban, or the last lunar month before Muslims begin fasting for Ramadan.
When & where to see the Flower Moon
One interesting characteristic Northern Hemisphere observers may notice about the full moon is that it will be in the sky for a shorter period than the sun. This is because the full moon, being opposite from the sun as it peaks, occurs in the part of the sky that is below Earth's celestial equator, so it traverses a shorter path from horizon to horizon as it rises and sets.
In New York City, for example, the Flower Moon will rise at 5:55 a.m. from the southeast horizon, 108 degrees from north (measured clockwise, with east at 90 degrees). The following morning, it will set at 6:29 a.m. in the southwest, 251 degrees from north. The sun, meanwhile, will rise at 5:44 a.m. on May 10 at 79 degrees of azimuth (or 11 degrees north of east), and sets at 8:02 p.m. at the 282 degree mark (12 degrees north of west). While the sun will spend 14 hours and 18 minutes in the sky, the moon will be above the horizon for only 10 hours and 39 minutes. [How to Measure Distances in the Night Sky]
The difference is more pronounced the farther north one goes. From Reykjavik, for example, the Flower Moon will not get more than 15 degrees above the horizon, whereas from New York, the moon's altitude will be 37.8 degrees above the horizon at 12:26 a.m., when it will be at its highest point in the sky. The effect is reversed for Southern Hemisphere viewers – in May, Australians are readying for winter, and the days are getting shorter while the sun is low in the sky. The full moon, meanwhile, will be higher in sky and spend more time above the horizon.
This can make for some spectacular moon photographs – when the moon is closer to the horizon it looks bigger with something in the picture to give it scale, like landscapes or cityscapes. Often the moon will look a bit redder in the Northern Hemisphere during warmer months, as the moonlight has to travel through more atmosphere to reach one's eyes. The best times for these effects, though, are usually near the rising and setting times. [Moon Photography Tips from Astrophotographers: A Visual Guide]
May's full moon won't be passing any planets the way April's Pink Moon met Jupiter in the night sky last month. On the other hand, the full moon will be in a relatively dim patch of sky as it passes in front of the constellation Libra, which means it will stand out that much more.
Editor's Note: If you capture an amazing photo of the Pink Moon and want to share it with Space.com for a story or gallery, please send images and comments in to managing editor Tariq Malik at email@example.com.
This story was updated on May 10, 2017.