The luminous lunar spectacle called a "super moon" occurs this weekend, and if the clouds part, tri-state area sky watchers could receive an unusually good view of the biggest full moon of the year.
The moon becomes full at 10:34 p.m. Saturday. A minute later, the moon reaches its lunar perigee -- its closest approach to Earth.
"It's a pretty sight if you get a clear night," said Kenneth McLaughlin, professor of physics and engineering at Loras College.
Here are five things to know about the unusual celestial show.
1 What's going on?
We say "super moon," scientists say "perigee-syzygy of the Earth-moon-sun system."
The elliptical nature of the moon's orbit leads to the phenomenon.
"The moon is in an orbit around the Earth and that orbit is not perfectly circular," McLaughlin said. "If you were to look at a scale model of the planets, you would be hard-pressed to see that they are not circular, because the degree that they look elliptical is very modest. The same goes for the moon."
The closest lunar approach to Earth is its perigee. The farthest lunar approach is called the apogee.
2. Bigger and brighter
The moon's elliptical orbit brings it within 221,802 miles of Earth this weekend, and the full moon will appear as much as 14 percent bigger and 30 percent brighter than other full moons of 2012, according to NASA.
"It's a subtle effect, and that effect tends to make the moon look broader across its middle because it's closer," McLaughlin said.
3. Higher tides
Full moons cause high tides, and the moon's approach in perigee does, too.
Donald Olson, an astronomer at Texas State University-San Marcos, theorized that a super moon on Jan. 4, 1912, could have created tides so unusually strong they drew icebergs south into the Atlantic shipping lanes, just in time for the Titanic's ill-fated maiden voyage. However, the National Oceanic and Atmospheric Administration says lunar gravity at perigee pulls most tidal waters only an inch or so higher than usual.
4. Full moon = crazy night
Where do you think the word "lunacy" comes from?
Full moons have long been associated with strange behavior, and "lunacy" derives from the Latin name for moon. However, most modern studies fail to find a correlation between the phase of the moon and the incidence of crime, sickness or human behavior.
5. Rain, rain go away
There's a chance we might not see this weekend's lunar show.
"It doesn't look like a real good viewing opportunity," said Tom Olsen, a hydro-meteorologic technician with the Quad Cities office of the National Weather Service.
Olsen predicts a 70 percent chance of cloud cover throughout the weekend, limiting opportunities to glimpse the super moon.
"You might see it occasionally," he said.