The Moon was officially full late Sunday night, but to the untrained eye it appears full for a day or two on each side. In reality, the Moon is never really full. So go ahead, swoon to the "Full Moon" with your Valentine.
At full Moon, the satellite is exactly opposite the Sun in our sky. From our surface perspective at sunset, the Moon is rising and it reflects a full disk of sunlight directly to our eyes. The Moon arcs across the sky and sets at sunrise.
The night after it is full, the Moon rises later, typically by about 50 minutes, depending on the season and your latitude.
At last quarter--a week after the full phase--the Moon appears as a backward "D" and does not rise until midnight, remaining in the morning sky until Noon.
Hard to tell
But tonight and Tuesday night, you'd have to look closely to tell if it is still full or not.
The Moon was officially full Feb. 12 at 11:44 p.m. EST.
One minute before that time, it was a waxing gibbous; one minute after that time, it was in the waning gibbous phase.
Here's the tricky part: The Moon can appear 100 percent sunlit from Earth only if it is diametrically opposite to the Sun in the sky. But at that moment the Moon would be positioned in the middle of Earths shadow--and in total eclipse. So in any month when there is no eclipse, there is an ever-so-slight sliver of darkness somewhere on the lunar limb throughout those hours--or that moment--when the Moon is passing through "full" phase.
The Moon is never really full.
Because the plane of the Moon's orbit is inclined 5 percent with respect to the plane of Earth's orbit around the Sun, eclipses occur only every few months when the orbits are lined up just right.
From lore, this month's full Moon had the name of the Snow Moon, appropriate in light of the weekend weather in the Northeast. The name was given to a Moon that comes during a time when the heaviest snows typically fall. Hunting is difficult this time of year, so it also carries the name of the Hunger Moon.
The next full Moon will be March 14 at 6:35 p.m. EST. It will be the Worm Moon, coming at a time when the ground tends to soften and earthworm casts reappear, inviting the return of the robins. It's also known as Crow, Crust and Sap Moon, marking the time of tapping maple trees
With the March 14 full Moon comes a very minor penumbral lunar eclipse. The Moon will pass through the Earth's outer shadow and cause a slight tarnishing or smudginess to appear on its lower rim. The darkest phase of this eclipse comes at 6:48 p.m. EST. For about 40 minutes before and after this time, the subtle penumbral shading may be detected with binoculars and even the naked eye.
This article is part of SPACE.com's weekly Mystery Monday series. SPACE.com's Senior Science Writer Robert Roy Britt and Night Sky columnist Joe Rao contributed.
- Sky Calendar and Moon Phases
- Full Moon Fever: Lunar News and Lore
- The Disappearing Moon: Why and Where it Hide
- Skywatcher's Guide to the Moon
- The Fallacy of the Full Moon