Friday, May 4, 2012

Return of the Super Moon

Skywatchers take note: The biggest full moon of the year is due to arrive this weekend.

The moon will officially become full Saturday (May 5) at 11:35 p.m. EDT. And because this month's full moon coincides with the moon's perigee — its closest approach to Earth — it will also be the year's biggest.

The moon will swing in 221,802 miles (356,955 kilometers) from our planet, offering skywatchers a spectacular view of an extra-big, extra-bright moon, nicknamed a super moon.

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Okay, the Moon is 14% bigger than usual, but can you really tell the difference? It's tricky. There are no rulers floating in the sky to measure lunar diameters. Hanging high overhead with no reference points to provide a sense of scale, one full Moon can seem much like any other.

The best time to look is when the Moon is near the horizon. For reasons not fully understood by astronomers or psychologists, low-hanging Moons look unnaturally large when they beam through trees, buildings and other foreground objects. On May 5th, this Moon illusion will amplify a full Moon that's extra-big to begin with. The swollen orb rising in the east at sunset should seem super indeed.
Folklore holds that all kinds of wacky things happen under the light of a full Moon. Supposedly, hospital admissions increase, the crime rate ticks upward, and people behave strangely. The idea that the full Moon causes mental disorders was widespread in the Middle Ages. Even the word "lunacy," meaning "insanity," comes from the Latin word for Moon.
This evening's Moon approaching full

The majority of modern studies, however, show no correlation between the phase of the Moon and the incidence of crime, sickness, or human behavior. The truth is, the Moon is less influential than folklore would have us believe.
Super Moon Superman Logo
It's true that a perigee full Moon brings with it extra-high "perigean tides," but according to the National Oceanic and Atmospheric Administration this is nothing to worry about. In most places, lunar gravity at perigee pulls tide waters only a few centimeters (an inch or so) higher than usual. Local geography can amplify the effect to about 15 centimeters (six inches)--not exactly a great flood.
This evening's Moon just before dark
This evening's Moon just before dark.

Super perigee Moons are actually fairly common. The Moon becomes full within a few hours of its closest approach to Earth about once a year on average. The last such coincidence occurred on March 19th, 2011, producing a full Moon that was almost 400 km closer than this one. As usual, no trouble was reported--unless you count a midnight awakening as trouble.

If so, close the drapes on May 5th. Otherwise, enjoy the super-moonlight.
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Unusual autumn warmth was spread across the United States and precipitation was scarce in October 2016 according to the monthly US summary released by NOAA;'s National Centers for Environmental Information (NCEI) this week.

Sea surface height anomalies (departures from average) during the northern-autumn phase of the last four La Niña events, including the one now beginning. Higher sea surface heights (red and white areas) are associated with warmer upper-ocean temperatures. Image credit: NASA imagery, compilation courtesy Jan Null, @ggweather, Golden Gate Weather Services.

Weak La Niña Expected to 
Persist into 2017

La Niña 2016-17 isn’t looking like a spectacular event. Model runs released this week from the North American Multi-Model Ensemble (see Figure 3 below) are in general agreement that this should bottom out as a weak La Niña event over the next several months, with SSTs gradually returning to the neutral range by late winter or early spring. In their joint predictions from early November, forecasters at NOAA and the International Research Institute for Climate and Society (IRI) call for neutral conditions to be the most likely state by the first quarter of 2017 (see Figure 4 below). Hints of a possible return to El Niño in 2017-18 are already showing up in the longest-range model runs. The NOAA/IRI outlook gives odds twice as high for El Niño (about 30%) as for La Niña (about 15%) by summer 2017, although neutral conditions remain the most likely outcome.