Serge B.’s photo of the Moon from Mississauga, Ontario.
Serge B.'s photo of the Moon from Mississauga, Ontario.
Monday’s Sugar Snow Sap Supermoon

On Monday afternoon, the Moon will reach its full phase as a “Supermoon.” What does that even mean?

On Monday afternoon at 1:48 pm EDT (or 17:48 Greenwich Mean Time) the Moon will reach its full phase.

Every culture around the world has developed its own set of stories for the Moon, and every month’s Full Moon tends to have one or more nicknames.

Serge B.’s photo of the Moon from Mississauga, Ontario.

According to the Ontario Native Literacy Coalition, the Ojibwe or Anishnaabe peoples of the Great Lakes region call the March Full Moon “Ziissbaakdoke-giizis” or Sugar Moon — “as the maple sap begins to run, we learn of one of the main medicines given to the Anishnaabe which balances our blood and heals us.”

It’s also known as “Onaabani-giizis,” or the Snow Crust Moon, and the coalition states Cree peoples call it “Mikisiwipîsim,” or the Eagle Moon — the month when the eagle returns. Europeans cultures call it the Worm Moon, Crow Moon, Sap Moon or Lenten Moon.

The March Full Moon always shines among or near the constellations of Leo (the Lion) or Virgo (the Maiden), which are half the sky away from the sun’s position in Aquarius (the Water-Bearer). Because the Moon can only appear full when it sits opposite the Sun in the sky, full Moons always rise in the east at sunset, and set in the west at sunrise. That full-on illumination by the Sun’s light causes the Moon’s geology to be enhanced, especially the contrast between the ancient cratered highlands and the younger, darker, smoother maria. Last month, I wrote here about the many interesting and easy-to-see features on the Full Moon.

The Moon’s full phase will be peaking near mid-day on Monday in the Eastern Time Zone, so observers living in that region will see the Moon as slightly less than full on Sunday evening. Binoculars will reveal a thin strip of darkened Moon along the Moon’s western limb (that’s the Moon’s left side for northern hemisphere observers). The Moon will look completely full on Monday evening, but there will be a slim band of darkness curving along its eastern limb.

This Full Moon will occur half a day before perigee, the point in the Moon’s orbit when it is closest to Earth, generating high tides worldwide and making this the largest and brightest full Moon of 2020 — the first of three consecutive Supermoons.  Let’s look at why that is.

The Moon completes an orbit of the Earth every 27.3 days — so lunar perigees and apogees repeat on that interval. At perigee, the Moon is about 14 per cent closer to the Earth than at apogee, making it look a bit larger and brighter. Due to the Earth’s motion around the Sun, the lunar phases, including Full Moons, repeat every 29.5 days. (The Moon’s orbit time around Earth is called its sidereal period. The two-day longer phase cycle time is called its synodic period, from the Greek word synodikos – a meeting or conjunction of  people, or celestial objects.) 

About every 14 months, the lunar orbit and lunar phase cycles synchronize for a few months, giving us a series of Supermoons. (During that synchronization window, we also get corresponding apogee New Moons. But New Moons aren’t visible on Earth, unless a solar eclipse occurs. In fact, the June Supermoon will be followed by an annular solar eclipse on June 21 — where the Moon will be too far from Earth to completely block the sun, leaving an annulus of sun revealed around it.)

The term Supermoon was coined by an astrologer named Richard Nolle in 1979. He defined it to be a Full Moon that occurs when the Moon is within 90 per cent of its minimum distance from Earth. The term is not officially recognized by astronomers, because Supermoons are not really “super” at all. Beyond being somewhat brighter and larger, no unusual effects or phenomena arise from them, and most people wouldn’t realize one is happening if the media didn’t promote it.

Although it’s about seven per cent larger than average, don’t expect Monday night’s Moon to look much different, despite all the hype. Don’t forget that any Moon, even a Supermoon, can easily be covered by your pinky fingernail held at arm’s length and one eye closed. By the way — a syzygy is the astronomical term for an alignment of three celestial objects — in this case, the Sun, Earth and Moon. So this Full Moon will be a lunar perigee syzygy.

As an extra bonus, at 8:18 pm EST on Monday evening, a medium-bright star named Nu (ν) Virginis will pop out from behind the Moon, near the Moon’s top edge. The sight will be best seen in telescopes and strong binoculars. The time of egress varies depending on your latitude, so start watching a few minutes beforehand. For observers in Eastern Canada and the northeastern USA, the Moon will already be in view above the eastern horizon before it covers the star at 23:23 GMT, or 7:23 pm Atlantic Time. For the rest of the night, the Moon’s orbital motion will carry it farther from that star.

After Monday night, the Moon will wane in phase and rise later each night. The Moon will travel through Virgo (the Maiden) until Thursday night, when it will rise shortly before midnight local time among the stars of Libra (the Scales). Before dawn on the coming weekend, look for the waning Half Moon in the southern sky, sitting above the stars of Scorpius (the Scorpion). That Moon will also persist into the southern morning sky after sunrise.

Looking for more highlights about astronomical events in the coming days? Check out This Week’s Sky by Chris Vaughan.

Chris Vaughan is a science writer, geophysicist, astronomer, planetary scientist and an “outreach RASCal.” He writes Astronomy Skylights, and you can follow him on Twitter at @astrogeoguy. He can also bring his Digital Starlab portable inflatable planetarium to your school or other daytime or evening event. Contact him through AstroGeo.ca to tour the universe together.

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