Celebrate Cinco de Mayo 2012 under a supermoon!

Cinco de Mayo (Spanish for May 5th) is a day of Mexican heritage and pride that commemorates the Mexican army’s victory at the Battle of Puebla during the Franco-Mexican War in 1862. It’s a day of celebration! This year, on the night of Cinco de Mayo parties around the world, there will be a big full supermoon shining overhead.

Photo credit: Michelle Eve Photography

Supermoon? What’s a supermoon?

According to U.S. clocks, the full moon falls on May 5, 2012 at precisely at 10:35 p.m. Central Daylight Time. This same full moon falls on Sunday, May 6 at 3:35 Universal Time (UT) – the standard time at the prime meridian of 0o longitude, or, for example, in Greenwich, England.

What does supermoon mean exactly? And how special is it?

For one thing, the word supermoon didn’t originate in astronomy. 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. Also, in skylore, the May full moon is known as the Milk Moon. Each full moon has its own name.Here are the names of all the full moons But the term supermoon doesn’t stem from skylore, either, as other moon names do.

Instead, the term supermoon came from astrology. Astrologer Richard Nolle of the website takes credit for coining the term supermoon in 1979. He defined it a new or full moon that occurs with the moon at or near (within 90% of) its closest approach to Earth in a given orbit (perigee).

In short – on the night of a supermoon – the Earth, moon and sun are all in a line, with the moon in its nearest approach to Earth for that month.

Because it’s at its closest to Earth, a supermoon is bigger than other full moons. The supermoon of March 19, 2011 (right), compared to an average moon of December 20, 2010 (left). This image shows the size difference. Will you eye be able to detect a bigger moon on May 5? People argue about this, but most astronomers say no. Image Credit: Marco Langbroek, the Netherlands, via Wikimedia Commons.

By Nolle’s definition, there are 4-6 supermoons a year on average. That doesn’t sound very special, does it? That’s because it’s really not all that special.

In fact, the May’s full moon lines up much more closely with perigee – the moon’s closest point to Earth – than Nolle’s original definition. The 2012 May full moon falls within an hour of perigee. At perigee, the moon lies only 356,955 kilometers (221,802 miles) away. Later this month, on May 19, the moon will swing out to apogee – its farthest point for the month – at 406,448 kilometers (252,555 miles) distant. So you can see the May 5 moon really is at its closest for the month of May.

In fact, May 2012 presents the moon’s closest encounter with Earth since March 19, 2011, at which time the moon was a scant 380 kilometers closer to Earth. The moon won’t come as close as the May 5 extra-close moon until August 10, 2014 – although in 2013 the moon at its closest (June 23, 2013) will lie only 36 kilometers farther away than the closest moon in 2012. (See table below) Maybe this helps you see that supermoons – while interesting – are fairly routine astronomical events.

What does all this have to do with Cinco de Mayo? Only this. This supermoon happens to coincide with Cinco de Mayo, an important celebration in Mexican culture. In 2012, outdoor Cinco de Mayo parties on Saturday, May 5, will feature a full supermoon shining overhead! It should be very beautiful. Happy Cinco de Mayo, everyone!

Bottom line: The full moon of May 5 (or 6), 2012 is the closest and largest full moon of this year. Many posts online are already calling it a supermoon. The May 5, 2012 supermoon coincides with Cinco de Mayo, an important date in Mexican culture and a day on which many celebrate!

Understanding the full moon

Moon facts at your fingertips

Did a supermoon cause the 2011 March 11 earthquake in Japan?

May 3, 2012

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