The largest full moon of 2013, a so-called "supermoon,"

The largest full moon of 2013, a so-called "supermoon," will light up

the night sky this weekend, but there's more to this lunar delight

than meets the eye.

On Sunday, June 23, at 7 a.m. EDT (1100 GMT), the moon will arrive at

perigee — the point in its orbit bringing it closest to Earth, a

distance of 221,824 miles. Now the moon typically reaches perigee once

each month (and on some occasions twice), with their respective

distances to Earth varying by 3 percent.

But Sunday's lunar perigee will be the moon's closest to Earth of

2013. And 32 minutes later, the moon will officially turn full. The

close timing of the moon's perigee and its full phase are what will

bring about the biggest full moon of the year, a celestial event

popularly defined by some as a "supermoon."

You can watch a free webcast of 2013 supermoon full moon on SPACE.com

on Sunday at 9 p.m. EDT (0100 June 24), courtesy of the skywatching

website Slooh Space Camera.

While the exact time of the full moon theoretically lasts just a

moment, that moment is imperceptible to casual observers. The moon

will appear full a couple of days before and after the actual full

moon most will speak of seeing the nearly full moon as "full": the

shaded strip is so narrow, and changing in apparent width so slowly,

that it is hard for the naked eye to tell in a casual glance whether

it's present or on which side it is.

During Sunday's supermoon, the moon will appear about 12.2 percent

larger than it will look on Jan. 16, 2014, when it will be farthest

from the Earth during its apogee.

Supermoon's big tides

In addition, the near coincidence of Sunday's full moon with perigee

will result in a dramatically large range of high and low ocean tides.

The highest tides will not, however, coincide with the perigee moon

but will actually lag by up to a couple of days depending on the

specific coastal location. [The Moon Revealed: 10 Surprising Facts]

For example, for New York City, high water (6.3 feet) at The Battery

comes at 8:58 p.m. EDT on Sunday, or more than 12 hours after perigee.

From Cape Fear, N.C., the highest tide (6.5 feet) will be attained at

9:06 p.m. EDT on Monday, while at Boston Harbor a peak tide height of

12.3 feet comes at 12:48 a.m. EDT on Tuesday, almost 2 days after the

time of perigee.

Any coastal storm at sea around this time will almost certainly

aggravate coastal flooding problems. Such an extreme tide is known as

a perigean spring tide, the word spring being derived from the German

springen, meaning to "spring up," and is not — as is often mistaken —

a reference to the spring season.

Spring tides occur when the moon is either at full or new phase. At

these times the moon and sun form a line with the Earth, so their

tidal effects add together (the sun exerts a little less than half the

tidal force of the moon.) "Neap tides," on the other hand, occur when

the moon is at first and last quarter and works at cross-purposes with

the sun. At these times tides are week.

Tidal force varies as the inverse cube of an object's distance. We

have already noted that this month the moon is 12.2 percent closer at

perigee than at apogee. Therefore it will exert 42 percent more tidal

force at this full moon compared to the spring tides for the full moon

that will coincide with apogee next January.

Huge moon at moonrise

Usually the variation of the moon's distance is not readily apparent

to observers viewing the moon directly.

Or is it?

When the perigee moon lies close to the horizon it can appear

absolutely enormous. That is when the famous "moon illusion" combines

with reality to produce a truly stunning view. For reasons not fully

understood by astronomers or psychologists, a low-hanging moon looks

incredibly large when hovering near to trees, buildings and other

foreground objects. The fact that the moon will be much closer than

usual this weekend will only serve to amplify this strange effect.

So a perigee moon, either rising in the east at sunset or dropping

down in the west at sunrise might seem to make the moon appear so

close that it almost appears that you could touch it. You can check

out this out for yourself by first noting the times for moonrise and

moonset for your area by going to this website of moonrise times by

the U.S. Navy Oceanography Portal.

Happy moon-gazing!





Read more: http://www.foxnews.com/