Super Moons are really a Big Deal

Each year, people around the world look to the night sky for a special event- the “super moon.”   For skywatchers and science enthusiasts alike, the chance to witness the phenomenon causes great excitement.  But, what actually is a super moon?  Some think it’s a trick of the moonlight; however, super moons are more than that.

What is a super moon?

The term super moon was coined by astronomer Richard Nolle a few decades ago.  Nolle, like so many others before him, noticed that some full moons or new moons look larger than others.  He began calling these phenomena super moons, which are simply full or new moons occurring at times when the moon is closer to the Earth and appearing larger than normal to the human eye.

When the moon goes through its cycle, it orbits around the Earth in 27 days; however, the phases of the moon, from new to new, take 29.5 days.  As sunlight reflects off the moon’s face, the human eye perceives the different amounts of light and angles as the phases.  When the entire half of the moon is lit, which is 14 days into its cycle, the moon is considered “full.”  When a full moon occurs at the point the moon’s orbit brings it closer or closest to Earth (perigee), that moon is a super moon. These super moons are defined as those full moons which occur within 90% of perigee.

What makes them super?

The moon appears smallest when the moon is farthest away from the Earth, or at apogee, but when the moon moves closer, it appears to grow in size.  The difference between apogee and perigee can be as little as 30,000 miles, which is not very much on the cosmic level, but enough to make the moon look very different. At perigee, the point the moon is closest to the Earth; the moon appears considerably larger, up to 15%, and considerably brighter, up to about 30%, than it would when it is at apogee.

Super moons also appear super large to the human eye depending on our own points of reference.  When a full moon is near the horizon, it appears larger than it does in other parts of the night sky.  The same can be said of a super moon.

Differences in super moons

Nolle predicted that super moons occur four to six times a year on average.  So far in 2013, there have been three super moons – one in May, June, and July. And another is expected in December 2013.   

When the moon is at proxigee (the absolute closest perigee of the year), the largest super moons occur. These biggest super moons are sometimes called perigee full moons and occur once every one year, one month and 18 days. The last such super moon occurred in June 2013. The next perigee full moons will occur in August 2014, September 2015, and November 2016.

The super moon expected in December 2013 will not be a full moon. It will be a new moon.  New moons can be super moons as well.  They are harder to see and may not be as interesting to most.  Super new moons are the opposite of super full moons.  They occur when the Moon is at the start of its phase and closest to the Earth.  Within 14 days of this special December super moon, sky watchers will see a very small full moon, because the moon will be in apogee.

The sun also has its part to play in the size and splendor of a super moon. The moon-Earth perigee distance will depend on where the Earth is in its orbit around the sun, also. With stronger pull from the sun, the moon often dips even closer to the Earth.  In these cases, winter super moons are generally more spectacular than those that occur in summer.

While many may expect higher tides and other moon related phenomenon during the next super moon, others will certainly appreciate the wonder of this interesting phenomenon.  And, like stargazers and scientists alike, you may find that a super moon is really a “big deal.”