Illustration of the position of the Earth's moon at apoggee and perigee.Supermoons get lots of publicity from the media, but is there anything to them beyond the hype? If the term "supermoon" bothers you because it's not an official astronomical term, don't throw up your hands. You can turn supermoon lemons into lunar lemonade for your star party visitors by using it to illustrate astronomy concepts and engaging them with great telescopic views of its surface!
source image credit: NASA (Earth) Gregory R. Revera (Moon)
source image credit: NASA (Earth) Gregory R. Revera (Moon)
Many astronomers find the frequent supermoon news from the media misleading, if not a bit upsetting! Unlike the outrageously wrong "Mars is as big as the moon" pieces that appear like clockwork every two years during Mars's close approach to Earth, news about a huge full moon is more of an overstatement. The fact is that while a supermoon will indeed appear somewhat bigger and brighter in the sky, it would be difficult to tell the difference between an average full moon and a supermoon with the naked eye.
Image Credit: Science@NASA
There are great bits of science to glean from supermoon discussion that can turn supermoon questions into teachable moments. For example, supermoons are a great gateway into discussing the shape of the moon's orbit, especially the concepts of apogee and perigee. Many people may assume that the moon orbits Earth in a perfect circle, when in fact its orbit is elliptical! The moon's distance from Earth constantly varies, and so during its orbit it reaches both apogee (when it's farthest from Earth), as well as perigee (closest to Earth). A supermoon occurs when the moon is at both perigee and in its full phase. That's not very rare; a full moon at closest approach to Earth can happen multiple times a year, as you may have noticed.
Image of the supermoon meaurement activity. (credit: NASA/JPL)
While a human observer won't be able to tell the difference between the size of a supermoon and a regular full moon, comparison photos taken with a telephoto lens can reveal the size difference between full moons. NASA has a classroom activity where students can measure the size of the full moon month to month and compare their results: "Measuring the Supermoon. "
Apparent size difference between a "supermoon" (left, full moon at perigee) and "minimoon" (right, full moon at apogee). This is an example of the comparisons curious individuals can make with a DSLR camera following this activity. Photo credit: NASA
Student can use digital cameras (or smartphones) to measure the moon, or they can simply measure the moon using nothing more then a pencil and paper! Both methods work and can be used depending on the style of teaching and available resources. Find out more here:https://www.jpl.nasa.gov/edu/teach/activity/measuring-the-supermoon
Apparent sizes of the Sun and moon depicted to scale at apogee (top right) and perigee (bottom).
There is actually is a way for naked eye observers to observe the different apparent sizes of the moon in our sky, but oddly enough it's not when the moon is full and brilliant, but the opposite: when the moon is new and dark, during eclipses! For eclipse chasers, the apparent size of the moon matters very much to what they will see. For example, a total eclipse can happen in conjunction with a supermoon as many in the USA saw on August 17, 2017. The apparent size of the moon was large enough to completely block the disc of the sun in our skies along a narrow path for a couple of minutes. If the moon was further away from the Earth, especially if it was at apogee- its furthest point - then a total eclipse would not occur. Instead, an annular eclipse would be seen instead, where a "ring of fire" would seem to circle the black disc of the new moon.
Image Credits: Dale Cruikshank (Annular Ecllipse)/ NASA/ Aubrey Gemignani (Total Eclipse)
This discussion of the different phases of the moon and can also make for a fun, simple, long-term project for a classroom. Students can observe the phases of the moon every day (when weather permits) over a thirty day period and write down their observations of the moon's phases and what times of day and night they can actually see the moon during this period. This can also be paired at some point with the crafty "Make a Moon Phases Calculator and Calendar" activity. You can find out more about the "Observing the Moon" classroom activity at: https://www.jpl.nasa.gov/edu/teach/activity/observing-the-moon
A related moon phases activity, which is short and perfect for small interactive groups. can be found at: https://www.jpl.nasa.gov/edu/teach/activity/moon-phases/
You can find a more detailed discussion of the science of supermoons on NASA's "What is a Supermoon and Just How Super Is It?" page from their "Teachable Moments" blog. You can find links to the above activities there, along with more lunar science that can be used to make the hype about Supermoons teachable moments for your star party visitors.
The next supermoon arrives the night of January 1, 2018 - a perfect time to ring in the new year with some solid lunar science!
Last Updated: December 14, 2017
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