SOLAR CALENDAR

People ask what the name “Heimhenge” really means. The “Heim” part should be obvious. The “henge” part needs some explanation. You have heard, I’m sure, about Stonehenge. Well, to earth-shelter our home on the side of this mountain required blasting out some 1000 cubic yards of rock. We used some of it to create fill extending our yard. We used some for landscaping. That left a good pile yet to be disposed of. It’s an interesting type of rock … metavolcanic basalt, or so the geologist told us. It has a nice gray-green color (dark green when wet) with veins of milky quartz. I tried selling it to some landscaping companies, but rock is just too common around here. Even the good landscaping variety goes for only dollars per ton … hardly worth hauling to another site. So we decided to use some of the remaining rock to create our own Stonehenge. After some careful surveying, we set a few of them up in our front yard to mark the equinox and solstice settings of the Sun. The images that follow show how it works.

3rocks The Three Henge Rocks
This is an overhead view of the Henge rocks. The large rock on the left is the Shadow Rock; the one on the right is the Equinox Rock; the one at the top is the Winter Solstice Rock. At 100-200 pounds each, they were muscled into position after setting up the alignments using geometry. The Shadow Rock required a backhoe to properly position. The angle between these rocks is 28º, the tilt of the Earth plus a 5º latitude correction factor.
W-solstice-1 Winter Solstice (December 21st)
It’s tough to shoot both the Sun and the landscape in a single image without under- or over-exposing something, but this one worked out alright after masking the sky and tweaking the gamma. The disc of the Sun has been painted into the image at the origin of the visible rays — the actual Sun was behind that cloud. Sunset on the Winter Solstice is at azimuth 242º, 28º south of west, what some would call “WSW.” This view is from the Shadow Rock looking toward the Solstice Rock.

Most people notice the days getting shorter as winter approaches, but few (other than astronomers) pause to think about why this happens. Sunrise on this date is 28º south of east. These far-south sunrise and sunset points cause the Sun to take a lower path through the sky compared to other seasons. The result is only 146º of the 360º ecliptic (path of the Sun) is visible. This in turn results in 9 hours 45 minutes of daylight. On the Equinox, for comparison, the Sun rises exactly East, sets exactly West, 180º of ecliptic are visible, and there are 12 hours of daylight.

W-solstice-2 Winter Solstice (December 21st) – Reverse View
After taking the above image, I reversed the view and shot back toward the Shadow Rock. You can see the alignment is right on. This was a fairly bright sunset for the Winter Solstice, with good contrast and sharp shadows. Just before the Sun dropped below the mountains it emerged from behind the cloud that hid it in the above image. Less than a minute after this image was captured the direct rays were gone.
equinox Equinox (March 20th and September 23rd)
Twice each year this shadow alignment occurs. The Equinox Rock, slightly out of picture to right, casts its eclipse on the Shadow Rock, as you can clearly see. To get these pictures I need to have a clear sunset happening on the correct date. It doesn’t always all come together like this … this was a good one. It’s even tougher on the Winter Solstice, which took three years to get due to the usually cloudier weather on that date.
S-solstice Summer Solstice (June 20th)
Spooky. The Sun sets so far north on this date (azimuth 298º in AZ) the house was in the way, so I never even attempted to set up a Summer Solstice Rock. But on a clear solstice sunset one year, I noticed the southwest corner of the house cast a shadow on the Shadow Rock. Because of the distance to the house, the shadow on the rock is too diffuse to photograph, but the eyes can see it. So instead of trying to capture the shadow I just reversed the frame of reference. What you see here is the view of the setting sun from behind the rock. The alignment is near perfect.

That alignment was not planned. The spirits of Druids walk among us here at Heimhenge.