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 as full in the June 22 evening sky as it does on the evening of 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. In other words, it’s not just a supermoon. It’s the closest supermoon of 2013.
At United States’ time zones, 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 perigeedescribes 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 the term supermoon, which we’d never heard before. 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? Follow the links below to find out.
What is a supermoon?
How super is this supermoon?
How often is moon both full and closest to Earth?
Will the tides be higher than usual?
Your best photos: May 2013 supermoon
Does a supermoon have a super effect on us?
Big sun-diving Comet ISON might be spectacular in late 2013
View larger. | Astronomers say it’s tough to notice the difference in size between a supermoon and any other full moon. But photographs show it. 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 via Marco Langbroek, the Netherlands, via Wikimedia Commons.
What is a supermoon? The word supermoon didn’t come from astronomy. Instead, it came from astrology. Astrologer Richard Nolle of the website astropro.com takes credit for coining the term supermoon. In 1979, he defined it as:
…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.
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 22-23 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 on June 23. 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
How super is this supermoon? June 2013 presents the moon’s closest encounter with Earth until August 10, 2014, at which time the moon will be a scant 5 kilometers closer to Earth. The full moon will come even closer to Earth on September 28, 2015 (356,877 kilometers) and closer yet on November 14, 2016 (356,509 kilometers). November 2016 will feature the closest full moon until November 25, 2034! Maybe this helps you see that supermoons – while interesting – are fairly routine astronomical events.
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