I must admit to being a moon freak. When I am up at the lake in the summertime, much planning of my fishing schedules revolves about the phases of the moon and when the moon rises and sets. For years I have followed the generalization that with a monthly lunar cycle the moon rises a bit less than an hour later and sets roughly an hour later each night. Boy, have I been wrong!
My education began in 2006, when in the early summer I noticed that even during the period of a full moon, the moon barely ascended over the horizon throughout its circuit through the night. I also realized that the moon didn’t come up an hour later each night and that the time from moonrise to moonset wasn’t very long. Then one night the next winter I looked at the full moon, and it hit me that the moon was directly overhead and not near the horizon, where it was at the same time of night in the summer. These observations led me to an exploration of moon cycles that opened my eyes to something that I had never paid close attention to over many decades of night fishing for walleyes. It also got me to wondering about how variations in moon cycles might affect night fishing success.
After reading a bunch of articles on lunar orbits, I first realized that my original observations were correct. The second thing that I realized is that lunar orbits are much more complex than I had ever imagined. Let’s start with a few facts. In northern Minnesotda, the time between the rising and setting of the full moon in June, 2006 was only 7 hours and 50 minutes, whereas in December the full moon with its high arc in the sky was above the horizon for 17 hours and 12 minutes, according to data from the US Naval Observatory. In addition to having a low arc, the June full moon rises and sets far to the south as compared with the December full moon.
Two kinds of cycles determine how far toward the north or south the moon comes up and how high it rides in the sky. The first is a monthly cycle that for the moon acts very much like the yearly cycle of the sun. On the December solstice (our shortest day), the sun comes up far to the south and traces only a low arc across the sky until it sets quite far south. Then as the seasons progress, toward the first day of summer, the sun rises earlier, much farther to the north, and is high in the sky at noon. The moon orbit goes through two similar cycles. One is completed every 29.5 days instead of throughout an entire year. In June, the full moon is low in the sky, and the thin crescent moon that is seen a bit over two weeks later rides high. Over the next six months, things undergo a gradual reversal so that by December the full moon rides highest (almost directly overhead), and the crescent moon follows the lowest arc across the sky. The second lunar cycle, which is most apparent by looking at the full moon, takes place over a year. In their yearly cycles, the arcs of the sun and full moon are basically the opposite, so that in June, when the arc of the sun is highest, that of the full moon is lowest, whereas in December the arc of the sun is lowest and that of the moon is highest.
To make things even more complicated, there is an 18.6-year cycle that also affects the arc of the moon as an add-on to its monthly cycles. In the year 2006, the difference between a high and low lunar arc was the greatest. In other words, the height of the high December arc was the highest in 18 years, and the low June arc was the lowest. Nine years later (2015), the difference between the highest and lowest moon arc was the least. By 2024, the difference will be greatest again.
How might all of this affect the fisherman? At one level, in a period such as June, 2006, when the arc of the full moon is lowest, there is less time at night when one can fish by the light of the moon. Also, in June the moon rises and sets less than an hour later the next day, whereas in December the day-to-day difference is well over an hour.
The height of the moon’s arc also affects the amount of light that it casts. When the moon rides low in the sky, the intensity of its light is less because of the filtering effect of small particles in the atmosphere, whether dust or the haze of a warm front. This is the same thing that happens to sunlight at sunset. The angle of the moonlight hitting the water also influences how much light penetrates into the deeper waters because of increased reflection from the surface. Another little recognized fact about moonlight is that the intensity of light coming from a half moon is only 1/10 that of a full moon because of the way that the rays of the sun reflect off the sides of the moon’s surface. When you look at the silvery moon, you would never guess that its surface is actually black. The reason it looks silvery is that other than the narrow beam of sunlight hitting the moon, no other significant sources of light from space hit the moon. Under circumstances like this, even a black object (such as a piece of coal) looks silvery when a light is shined upon it.
Many fishermen strongly feel that there is a correlation between moon phases and fishing success. What has been little considered, if at all, is whether the height or duration of the arc of the moon across the sky has any influence on the feeding behavior of fish during the night (or the day, for that matter). It would be interesting to look at data on large fish caught to see if success is greater during parts of the 18.6-year cycle when the moon is highest or lowest in the sky. At a minimum, the behavior of the moon may influence the behavior of fishermen in terms of when they go onto the water and how long they stay. Whether the increasing duration and higher arc of the full moon as the seasons transition from summer to late fall has any effect on fishing is presently anybody’s guess. Many variables play a role in walleye fishing success, and the moon is certainly one of them.
