“Shine on, shine on harvest moon up in the sky. . .” so go the lyrics to the popular 20th century song. The harvest moon is said to be the full moon appearing closest to the autumnal equinox which signals the change in the seasons. EarthSky indicates that “depending on the year, [it] can come anywhere from two weeks before to two weeks after the autumnal equinox.” For 2013, this change is set to occur on Sep. 22, but a harvest moon is set to rise on the scene sometime between Wednesday, Sep. 18 and Thursday, Sep. 19 in the Northern Hemisphere.
When the night of the harvest moon coincides with the night of the equinox, it is called a "super harvest moon." Wunderground.com reported that back in 2010, the harvest moon occurred less than six hours after the autumnal equinox, creating the first super harvest moon since 1991 and the last one until 2029.
Often, the harvest moon seems to be bigger or brighter or more colorful than other full moons. The apparent larger size occurs because a low-hanging moon seems to be larger than one appearing higher in the sky. This phenomenon is called a moon illusion, and it can be seen with any full moon.
The golden glow of the moon shortly after it rises is the result of light from the moon passing through a greater number of atmospheric particles than when the moon is overhead. Salmonriver.com explains the phenomenon this way: “The atmosphere scatters the bluish component of moonlight (which is really reflected white light from the sun), but allows the reddish component of the light to travel a straighter path to one's eyes. Hence, all celestial bodies look reddish when they are low in the sky. Actually harvest moons are not brighter, smaller, or yellower than during other times of the year, but all full moons have their own special characteristics.”
Another lunar term is a “blue moon.” The expression “Once in a blue moon ...” usually refers to an event occurring not very often. The actual definition is said to be the second full moon to occur in a single calendar month. This of course, has nothing to do with the color of the moon, but the expression refers to the infrequency of such an occurrence.
Whether we speak of a "harvest moon," a "blue moon,: or a "blood red moon" or describe it in an array of other colors, a full moon is an amazing heavenly body to observe. Genesis describes the moon as being created by God: the lesser light to “rule the night.” Along with the sun the moon was created "for signs, and for seasons, and for days, and years." The moon in its various phases continues to inspire poets, lovers, children and others of every culture, especially as the seasons change. And so we sing, “Shine on harvest moon. . . .”
Check out these related articles regarding the moon:
"Super moon" appears this weekend: Local places to see heavenly bodies along with a slide show of "super moon" photos.