A rather special time regarding the moon is fast approaching. It is something called the Minor Lunar Standstill. The Earthworks in Newark, Ohio, within the Licking River valley are attuned to the lunar cycle, and that means some interesting opportunities are occurring as the moon aligns with Earthworks.
But I’m going to need to explain.
There are two major earthworks remaining in the valley containing Newark. They were built by the Hopewell about 2,000 years ago. However, the Earthworks were part of one huge complex that has been identified as an integrated lunar ceremonial site. [Updated: this originally said “lunar observatory”, but as Brad Lepper points out here, that really short-changes the breadth of what the earthworks were in all likelihood used for. To tell you the truth, though, I’m not sure there is any short phrase that would adequately describe its usage and cultural impact at the time.] Here’s a map made by James Salisbury (the inventor of the Salisbury steak) in 1862.
Here are some other blog entries of mine that discuss the Hopewell Earthworks:
The only remaining pieces (the rest were destroyed as the cities of Newark and Heath filled the valley) are the Octagon (with its attached circle) in the northwest, and the Great Circle (which was at one time the Licking County Fairgrounds) in the south.
You can get a feel for what the Newark/Licking Valley area looks like from this picture generated from LiDAR data, with the color indicating elevation, and I’ve added in the Earthworks. To get a sense of the size, that picture covers about 8½ by 11 miles. For the earthworks, the stuff in red is gone, with only the black remaining. The Earthworks were drawn in based upon what is left (which does show up nicely on LiDAR).
[Click for much larger version.]
The Octagon is aligned with the Major Lunar Standstill, while the Great Circle is (mostly) aligned with the Minor Lunar Standstill (and some of the legs of the Octagon also align with the Minor Lunar Standstill).
And now I have to explain the Standstills.
You are undoubtedly aware of the solstices (we just had one on December 21). As the sun (apparently) circles the earth, in the winter the sun rises and sets in the south, and doesn’t get very high in the sky. As the year progresses, the sun rises (and sets) further and further north, passing through the equinoxes (where it rises due east and sets due west) until it hits the summer solstice, rising and setting in the north. When it is at the solstices, it hangs around up north (or south) for quite a while, hence the word sol-stice (sun-stand, or the sunrises moving north come to a stop, stand there, and then retreat back south).
There are also lunistices.
They are based on the moon going around the earth, so they are a monthly cycle. The moon has northernmost rise/set points, and then half a month later, it has a southernmost rise/set points. There are also equi-somethings in-between. When at the lunistice, the moon rises (and sets) from nearly the same points for a few days, just as for a solstice the sun rises/sets from nearly the same points for a few days.
But there’s a twist.
You see, the orbit of the moon is not in the ecliptic (the plane that the earth revolves in) and the moon’s orbit is not perpendicular to the earth’s obliquity (the axial tilt that gives us seasons).
Here’s a picture that tries to show what is going on.
The sun is on the left. The earth is tilted compared to its orbit around the sun by 23.45°. However, the orbit of the moon is tilted 5.14° compared to the ecliptic. (By the way, the picture shows the winter configuration for the earth, with the southern hemisphere tilted towards the sun.) When this is the configuration, the moons rises as far north as it possible. This lunistice is the Major Lunar Standstill.
Now, as the moon orbits the earth, it does this (picture from a few days later):
I hope you can figure out that, as the earth rotates, the moon will rise less northerly than it did in the first picture, when the moon was at its lunistice.
Then as the moon continues around (getting more “new”), it rises more and more southerly, until it hits the southern lunistice and starts heading back up again. It really is like the seasons, but over a month (and it doesn’t affect the weather).
But there’s more.
You see, that tilted lunar orbit slowly rotates (precesses), with a period of about 18.6 years. It remains at 5.14°, but changes like a plate spinning on the floor. Thus about 2-3 years after the previous picture, it looks more like this.
And about 7 years into the cycle it looks like this
I hope you can see that the lunistices will be not quite as northerly as the earlier lunistices.
And then 9.3 years after the first picture, the moon’s orbit is tilted 5.14° below the ecliptic.
When the moon’s orbit is like this, this is the Minor Lunar Standstill. From here on, as the plane of the moon’s orbit keeps precessing, the moonrise at lunistice will slowly get more northerly again, completing the full cycle after 18.6 years.
If you rotate everything to see what’s going on from the perspective of the earth, the upper image shows the Major Lunar Standstill while the lower image shows the Minor Lunar Standstill.
I hope you can see how the lunistice moonrise is much more northerly in the first, and less so in the second.
OK. The main axis of the Octagon (with its attached circle) is perfectly aligned with the Major Lunar Standstill moonrise. That happened a little less than 9 years ago, in 2006.
But if you’ve been paying attention, you’ll realize that means that we are approaching the Minor Lunar Standstill. And we are. The full Minor Lunar Standstill occurs in October, but it is a Standstill. That means that things are really close even right now.
And that means that we can go to the Great Circle and observe it, which is what I did on New Year’s Eve. The moon ought to rise through the opening of the Great Circle during the Minor Lunar Standstill.
Here’s what the Great Circle looks like in LiDAR. At the center is what we call the “Eagle Mound” (but did the Hopewell intend it as an eagle? who knows).
You can see the opening at the upper right. I’ve also placed in there the Visitor’s Center, which is quite obvious if you stand on the Eagle Mound.
On the afternoon of New Year’s Eve, the moon rose just after 2:00pm. I was there with Tim Black, the official photographer for the Newark Earthworks Center. We were at the Eagle Mound, looking towards the opening and the Visitor’s Center.
We really couldn’t get the immediate moonrise. The sky was just too bright and there was a lot of glow on the horizon. (There are also a few trees in the way). But I’d like to start off showing this amazing picture from Tim.
[Picture by Tim Black. Used with permission.]
For this picture, he was standing to the left of the Eagle Mound, to avoid the tree (seen on the right) that was blocking the moon from us. In addition, in order to see through the horizon haze and brightness, he is using an infrared camera. You can see the Visitor’s Center, and the moon rising through a gap in the trees.
What I did was create a time-lapse movie. I took a picture every thirty seconds and then created an animated gif of the result.
You can see the Visitor’s Center sitting in the middle of the opening in the circle. The moon is not visible at first, but if you look carefully (the animation will keep looping), you’ll see the moon emerge from behind the tree.
You can also see how the path of the moon leads directly back to right over the Visitor’s Center.
[Click for a much better 900×600 pixel version; give it some time to load.]
I should note that we were about 3 days early for the lunistice. In Central Ohio in the Wintertime, you have to take your clear days when you can get them. On January 3rd, the moon would have risen from the left flank of the opening.
The experts are still debating just what the opening in the Great Circle is pointed at. Regardless, the opening is wide enought to encompass the Minor Lunar Standstill. Maybe it does even more (and there is speculation and discussion in that regard).
Regardless, I had the privilege to be there to witness the Great Circle doing part of what it was designed to do, over 2,000 years ago.
Ain’t that great?