9/18/02
The Naturalist's Corner
By Don Hendershot
“Shine
on, shine on harvest moon.”Harvest moon is the name for the full moon nearest the autumnal equinox. This year’s harvest moon will be September 21. The autumnal equinox is September 22.
It appears that since earliest man, cultures closely connected with the earth have recognized this time and this moon.
In our cycle of seasons there are two equinoxes; spring and fall. On these days, one in mid-March, the other in mid-September the sun rises due east, travels the celestial equator and sets due west. The equinox is a time of balance. There are 12 hours of day and 12 hours of night for everyone on the earth.
After the spring equinox (mid-March in our northern hemisphere) the days begin to lengthen and we slide into those long warm days of summer. After the summer solstice (the longest day), in June, days once again begin to shorten and the autumnal equinox, in September, marks that time of balance once more, before we slip into the long cold nights of winter.
It is the end of the growing season and the last harvest. Druids, Celts, and aboriginal people around the world found ways to celebrate and record this special time. There remains today a vast array of stone megaliths, stone circles and stone passages around the world that seem to track the movement of celestial bodies and mark the equinoxes.
There is no denying the change. As the earth tilts slightly, the sun moves farther southward, deserting the northern hemisphere. There is something different about the light. The change in angle casts a different shadow or reflects at a different angle.
There is a great stirring in the skies as migrant birds hurry to follow the sun southward. There is a sense of urgency as bears feed voraciously, putting on the fat that will see them through the winter; squirrels cache acorns and hickory nuts and farmers work tirelessly to harvest their crops before the killing frost.
The Cherokee call the September moon Duliidsdi, the nut moon. The nuts of the trees (chestnuts would have been a staple for the Cherokee) and the berries of the shrubs were harvested. The Ripe Corn Festival and the Brush Feast Festival were celebrated in autumn.
Myth has it the harvest moon is larger and brighter than any old ordinary full moon. The phenomenon is created by the geometry of the moon’s orbit around earth. Throughout most of the year the moon rises about 50 minutes later each evening. However due to the angle of the moon and the earth in the autumn, the moonrise is only about 10 minutes later each successive night. So the nearly full harvest moon is in the autumn sky several nights in a row.
Also the change in angle means the harvest moon climbs into the sky at a lower angle. It appears to hang on the horizon longer and since the light from the moon travels through more atmosphere near the horizon there is more refraction which creates the illusion of a larger moon. There is also another optical illusion. Since the moon is nearer the horizon the foreground of mountains, or trees, or buildings gives us a scale for comparison and makes the moon seem larger.
If you get out for a look at the harvest moon this weekend, take a minute and see if you can find Pegasus. The flying horse will be soaring above and just a little to the left of the moon in the east-northeast sky. Look for the Great Square that outlines Pegasus’ shoulder. The sides of the Great Square are nearly equal and the equidistant stars that make up each of the corners are equal in brightness. The four stars are Scheat, Markab, Algenib and Alpheratz.
(Don Hendershot can be reached at don@smokymountainnews.com)