The full moon of March — the Worm Moon — will occur in the eastern U.S. at 3:17 a.m. on March 18, (0717 UTC) according to the U.S. Naval Observatory (opens in new tab). In New York City the moon rises at 7:39 p.m. local time (opens in new tab), about 33 minutes after sunset.
The moon will be in the constellation Virgo. At 1:06 a.m. local time in New York (opens in new tab) on March 18 the just-before-full moon will cross the meridian, meaning it reaches the highest point in the sky, due south for Northern Hemisphere observers. At that point, it hits its maximum elevation, 54 degrees. In other cities, such as Chicago, Seattle, or San Francisco its elevation will be similar; there will also be small differences in the local time it reaches that elevation. In Chicago, for example, the moon crosses the meridian at 1:03 a.m. March 18 and reaches 53 degrees (opens in new tab), in Seattle, it will do so at 1:26 a.m. local time (opens in new tab) and will be at 46 degrees, in San Francisco it is at 12:14 a.m. and the altitude will be 71 degrees (opens in new tab).
Altitude is largely dependent on latitude; the lower one's latitude the higher the moon will appear in the sky. The hour depends on one's longitude. The moon's altitude will reach a maximum for observers at about 5 degrees latitude, which corresponds to cities such as Bogota, Cayenne, French Guiana, or Abidjan. As one moves further south its elevation will start to drop, though it will be towards the north — so in Sydney, Australia, which is at approximately 33 degrees south, the moon will be about 46 degrees high when it crosses the meridian at 12:37 a.m. on March 18.
What causes a full moon?
The full moon happens when the moon is exactly on the opposite side of the Earth from the sun. Unlike the timing of the moon's apparent position in the sky, the time of lunar phases depends on the position of the moon relative to the Earth and sun. That means the full moon occurs at the same time everywhere on Earth, with the hour and minute only changing because of time zones. So while the full moon is at 3:17 a.m. in New York, that will correspond to 6:17 p.m. the same day in Sydney.
Full moons are an easy target for binoculars or small telescopes, but they can be almost disappointing because the moon is so bright the surface loses contrast. One issue is the lack of shadows; we are seeing the lunar surface at noontime on the moon, so the sun (from the perspective of a person standing on the moon) is directly overhead. That said, moon filters are available that can make some features stand out. If one waits a few days after the full moon or observes a few days before, shadows bring out more detail.
The full moon happens two days before Venus reaches its greatest western elongation, meaning its largest apparent separation from the sun. As the separation is in the westward direction, it means Venus will rise well before the sun does. On March 18 Venus rises at 4:53 a.m. in New York (opens in new tab), while the sun comes up at 7:02 a.m.
Venus will be at magnitude -4.4, making it the brightest object in the sky after the moon. For observers in mid-northern latitudes, the planet will get about 15 degrees above the southeastern horizon by 6:30 a.m. local time. Skywatchers in more southern latitudes will have an easier time of it; as one moves south, the angle the path the planets take against the background stars is steeper relative to the horizon. In Mobile, Alabama, Venus rises at 4:37 a.m. (opens in new tab) local time and the sun rises at 6:29 a.m. (opens in new tab), so by a half-hour before sunrise the planet is 16 degrees high, and in Honolulu where the sun comes up at 6:37 a.m., the planet reaches 26 degrees by 6:00 a.m.
Mercury will also be a morning star, though it is much closer to the sun and thus much harder to observe. From New York (and other North American locales) the planet will only be 3 degrees above the horizon at sunrise (opens in new tab). Southern Hemisphere observers will see the planet rise much higher; in Sydney, for example, Mercury is 9 degrees above the eastern horizon by 6:30 a.m. local time; the sun rises at 6:56 a.m. on March 18.
Mars is also visible in the predawn sky, rising at 5:08 a.m. in New York on March 18 and reaching an altitude of 17 degrees by sunrise at 7:02 a.m. Looking southeast from New York City at about 6:00 a.m. one will see Mars and Venus paired, with Mars below Venus above and to the left of Mars. On the same date Sydneysiders will see the two planets much higher by 6:00 a.m. local time, about 33 degrees high in the east, with Mars higher and to the right of Venus.
Jupiter is effectively invisible; in New York, it rises at 6:49 a.m. and sets at 6:08 p.m. on March 18, so it's really a daytime object. Saturn is a bit easier; it rises in New York at about 5:40 a.m. local time and by sunrise is 14 degrees high in the southeast. Saturn will form a rough triangle with Venus and Mars, but it will still be a challenge to see it as it will be low to the horizon. Here again, Southern Hemisphere observers will have it easier; in Sydney Saturn will be about 20 degrees high by 6 a.m. local time with Venus above and to its left and Mars to the right.
The full moon shares the sky with several bright winter constellations. During the latter half of March Orion is visible the first half of the night, starting the evening high in the south by about 8 p.m. local time in mid-northern latitudes. Near Orion are Taurus and Gemini, and just to the southeast of Orion is Canis Major, the Big Dog, home to Sirius, the brightest star in the sky. All three constellations are bright enough that they don't get overwhelmed by the full moon, even in urban areas.
Looking east one will see Leo above the moon, and as one turns north one encounters the Big Dipper. Follow the "pointers" in the bowl of the dipper to Polaris, the Pole Star, and keep turning left to the western side of Polaris, to the distinctive "W" shape of Cassiopeia, the legendary queen and wife of Cepheus.
Why is the March full moon called the "Worm Moon"?
The March full moon is called the Worm Moon in the Old Farmer's Almanac, and that supposedly refers to the emergence of earthworms. North American Native peoples had other names for it. According to the Ontario Native Literacy Project, the Ojibwe (or Anishinaabe) peoples called it Ziissbaakdoke Giizas, the Sugar Moon, as it was when maple tree sap was harvested; this lunation also happens to mark the Anishinaabe new year.
The Tlingit of the Pacific Northwest calls the March full moon Héentáanax Kayaan'i Dís, or Black Bear Moon, or "underwater plants sprout" while the Haida called it Xitgáas Kungáay, or "Noisy Goose moon," according to the Tlingit Moon and Tide Teaching Resource (opens in new tab) published by the University of Alaska at Fairbanks.
In the southern hemisphere, March is the tail end of summer and the Māori of New Zealand described the lunar month in February to March (as measured between the successive new moons, with the full moon halfway between) as Paenga-whāwhā or "All straw is now stacked at the borders of the plantations," according to the Encyclopedia of New Zealand.
In China, the traditional lunar calendar (opens in new tab) calls the March lunation the second month, Xingyuè, the Apricot Month, for when the eponymous trees blossom. For some groups of Muslims the full moon will mark Lailat al Bara'ah, also called the Night of Forgiveness. In some Shia communities, the day is also noted for being the birthday of the Twelfth Imam
You can follow Space.com on Twitter @Spacedotcom and on Facebook.