(Picture courtesy of: http://tinyurl.com/mdscyfl)
We’ve all seen a full moon. They happen at the time of the month when the Sun, Earth and moon line up and the Sun’s light bounces off the moon for all the inhabitants of Earth to see. I thought that was the end of it. But a few weeks ago I heard about something called a “supermoon” on the news and decided to investigate. I found a website on earthsky.org that gave some good explanations while reporting on the supermoon that occurred on June 22 and 23, 2013.
A supermoon simply means the full moon coincides with the time when the moon is closest to the Earth in its orbit. Astrologer Richard Nolle takes credit for coming up with the term “supermoon” and by his definition, there are at least four to six supermoons every year. The reason the one this June was so special, however, was because it was the closest the moon will be to the Earth until August 2014, at approximately 356,991 kilometers (221,824 miles). So it was the “most ‘super’ supermoon of 2013.”
The reason no one really notices these supermoons is because the difference is very hard to discern with the naked eye. The pictures below show the difference that our eyes usually cannot make out.
“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).
This is significant because it reminds us that our moon’s orbit is not a perfect circle around the Earth. The most popular explanation of the moon’s origin is that when our planet was newly formed, a gigantic collision with another body created debris, which then started orbiting the Earth. Eventually the debris collected into the single body we now call the moon. This is called the Giant Impact Hypothesis, which best explains the Earth-moon system’s current orbital patterns, as well as why the moon’s chemical composition is so similar to Earth’s. But because of the moon’s slower orbit, it pulls on the Earth, slowly reducing Earth’s rotation. This tug-of-war between the Earth and moon also means the moon is slowly being pushed away from the Earth, about four centimeters a year.
If enough time were to pass, the moon would eventually drift away forever. The Sun will probably turn into a red giant (or a giant star in a late phase of stellar evolution) before that happens, though, and both moon and Earth will be destroyed by the expanding Sun. While the moon’s cycle may not always coincide with a month, we should always have our moon to light up our night sky. Pretty cool, huh?
(All information taken from: http://earthsky.org/tonight/is-biggest-and-closest-full-moon-on-june-23-2013-a-supermoon, http://www.space.com/3373-earth-moon-destined-disintegrate.html, or http://en.wikipedia.org/wiki/Origin_of_the_Moon)