| June 23rd |
Full moon falls on June 23, 2013 at 11:32 UTC (6:32 a.m. CDT in the U.S.). Thus, for many, the moon appears about equally full in the June 22 sky as it does on June 23. This full moon is not only the closest and largest full moon of the year. It also presents the moon’s closest encounter with Earth for all of 2013. The moon will not be so close again until August, 2014. At United States’ time zones, that means the moon will turn full on June 23 at 7:32 a.m. EDT, 6:32 a.m. CDT, 5:32 a.m. MDT and 4:32 a.m. PDT. We astronomers call this sort of close full moon a perigee full moon. The word perigee describes the moon’s closest point to Earth for a given month. Two years ago, when the closest and largest full moon fell on March 19, 2011, many used a term we’d never heard before: supermoon. Last year, we heard this term again to describe the year’s closest full moon on May 6, 2012. Now the term supermoon is being used a lot. Last month’s full moon – May 24-25, 2013 – was also a supermoon. But the June full moon is even more super! In other words, the time of full moon falls even closer to the time of perigee, the moon’s closest point to Earth. The crest of the moon’s full phase in June 2013, and perigee, fall within an hour of each other. What does supermoon mean exactly? And how special is the June 23, 2013 supermoon? Your best photos: May 2013 supermoon 
View larger.
| Astronomers say you can’t really tell the difference in size between a
supermoon and any other full moon. Check out this size comparison from
our friend Alec Jones in the UK.
The
supermoon of March 19, 2011 (right), compared to an average moon of
December 20, 2010 (left). Note the size difference. Image Credit: Marco
Langbroek, the Netherlands, via Wikimedia Commons.
…a new or full moon which occurs with the moon at or near (within 90% of) its closest approach to Earth in a given orbit (perigee). In short, Earth, moon and sun are all in a line, with moon in its nearest approach to Earth.By this definition, according to Nolle: There are 4-6 supermoons a year on average.What is a supermoon? That doesn’t sound very special, does it? In fact, the June 2013 full moon lines up much more closely with perigee – the moon’s closest point to Earth – than Nolle’s original definition. According to Guy Ottewell’s Astronomical Calendar 2013, the 2013 June full moon falls only 22 minutes after the moon reaches perigee, the moon’s closest point to Earth for this month and year. At perigee, the moon lies only 356,991 kilometers (221,824 miles) away. Two weeks later, on July 7, the moon will swing out to apogee – its farthest point for the month and year – at 406,490 kilometers (252,581 miles) distant.
Day and night sides of Earth at instant of June 23 full moon
Day
and night sides of Earth at instant of full moon (2013 June 23 at 11:32
Universal Time). In North America, the full moon is setting in the west
at sunrise. From eastern Asia, it’s rising in the east at sunset. The
full moon resides close to zenith – straight overhead – as seen from the Samoan islands in the central South Pacific Ocean. Image credit: Earth and Moon Viewer
Even the proximity of full moon with perigee isn’t all that rare. The extra-close moon in all of these years – 2011, 2012, 2013, 2014, 2015 and 2016 – finds the full moon taking place at or nearly the same hour as lunar perigee. More often than not, the closest perigee of the year comes on the one day of the year that the full moon and perigee most closely coincide. (See table below.) How often does the full moon coincide with perigee? Closest full moons recur in cycles of 14 lunar (synodic) months, because 14 lunar months almost exactly equal 15 returns to perigee. A lunar month refers to the time period between successive full moons, a mean period of 29.53059 days. An anomalistic month refers to successive returns to perigee, a period of 27.55455 days. Hence: 14 x 29.53059 days = 413.428 days 15 x 27.55455 days = 413.318 days This time period is equal to about 1 year, 1 month, and 18 days. The full moon and perigee will realign again on August 10, 2014, because the 14th full moon after the 2013 June 23 full moon will fall on that date.
Moon closest to Earth
For the moon to come closer than 356,400 kilometers (221,457 miles) is quite a feat. In fact, this won’t happen at all in the 21st century (2001-2100) or the 22nd century (2101-2200). The last time the full moon perigee swung this close to Earth was on January 14, 1930 (356,397 km), and the next time won’t be till January 1, 2257 (356,371 km). Will the tides be higher than usual? Yes, all full moons bring higher-than-usual tides, and perigee full moons bring the highest (and lowest) tides of all. Each month, on the day of the full moon, the moon, Earth and sun are aligned, with Earth in between. This line up creates wide-ranging tides, known as spring tides. High spring tides climb up especially high, and on the same day low tides plunge especially low.  Today’s extra-close full moon accentuates these monthly (full moon) spring tides all the more. If you live along a coastline, watch for high tides caused by the June 23 perigee full moon – or supermoon – over the next several days. Will the high tides cause flooding? Probably not, unless a strong weather system moves into the coastline where you are. Still, keep an eye on the weather, because storms do have a large potential to accentuate high spring tides. As a result, if you live near a coast, you’ll want to be on the lookout for higher-than-usual tides. Each full moon has its own name. Here’s a list. Because the moon – as always – shines opposite the sun in our sky at full moon, you’ll see the moon beaming all night tonight from dusk until dawn. This extra-close full moon is likely to usher in large tides along the ocean shorelines for the next several days, especially if these high tides are accompanied by strong onshore winds. Bottom line: The full moon of June 22-23, 2013 is the closest and largest full moon of this year. By a new definition – one that has just entered the world of astronomy from astrology – many will call it a supermoon. There are three full moons in 2013 that meet the definition of a supermoon – May, June and July. But this June 22-23 full moon is the most super of the supermoons! A super-duper moon! Understanding the full moon Looking for a tide almanac? EarthSky recommends . . . Moon facts at your fingertips Moon image at top of post: Alice Popkorn |
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