Wednesday, May 1, 2013

August 13 in April at Miantonomi's Cave

     Recently I returned to Miantonomi's Cave.  Here is a close-up of the  mark on the cave wall that was touched by the sun dagger in the equinox (almost) time lapse video (3/30/2013).  These two pieces protrude about 0.5 inch above the cave wall, and are about three inches apart.
 They are directly under the projecting stone.
The sun sets at the same position on the horizon twice every year, except for summer and winter solstices. There are 54 days from June 21 to August 13, and from June 21 back to April 28.  On April 28, the pattern of sunlight in Miantonomi's Cave would be similar to that on August 13, but there would be no foliage blocking the sunlight.  First  I returned on April 26.  The sky  was sunny when I left my home, and by the time I reached Miantonomi's Cave, it was obvious that Nature was not completely cooperative. This experience made me appreciate the difficulties of using sun patterns for determining important dates.
Luckily, the clouds kept breaking, and I obtained some photos and time lapse video. I returned on April 28, and this time, the clouds held off until about 6:45 PM.  The best pictures from both dates follow. The sun enters the large window first through the notch around 5:26 PM,
and then forms a large dagger that touches the first dimple around 6:30.  The dimples are marked above.
Around 6:35, the dagger touches the second dimple, and the second sun dagger appears. It is formed by light entering through the small window.
This second sun dagger moves upward, touching the crack in the wall.  The final pattern occurs at 7:04, when the light from the large window touches the end of the projecting stone.

It is easier to get a feeling for these events by watching the time lapse video made  4/26/2013. Clouds kept going past the sun,  making the sun daggers vanish and reappear, but the final sequence is clear. The video made 4/28/2013 shows the sequence of the sun dagger touching the dimples and the second sun dagger appearing and moving up the wall until the clouds blocked the light. The first sun dagger seems to disappear briefly after touching the second dimple. This also happened on 8/13/2012.  This was not caused by passing clouds, but probably by trees outside the cave.
     This is essentially the same pattern as on 8/13/2012, except then the foliage kept diffusing the light, instead of clouds.  I suspect there are two marks for equinox, and three dimples for August 13, to allow for estimation of days to these events, in case of cloudiness.

      I always notice something new whenever I return to the cave, something revealed by changes in light or season.  The projecting stone resembles an animal head from the side.  This time I  noticed something shiny along the line for the "mouth".  It even looked like there was a drop of water at the end of the stone.   The shiny area felt smooth, as if there were crystals there.

The veins of crystals are marked above.  Maybe this stone was chosen because the effect is like teeth shining in the half-light of the cave.
     Only 50 more days until summer solstice....

1 comment:

  1. August 13th is another event; and there are probably significant intermediate noteworthy dates. Agree that special techniques are needed in NE compared to the southwest. Many sites are using dawn as well as sunset.