Wednesday, April 3, 2013

Vernal Equinox (Almost) at Miantonomi's Cave

I have visited this cave many times and photographed sunlight forming daggers and other patterns on the cave wall.  While I have seen some distinctive patterns on August 13 and autumn equinox, the light  is diffused by the surrounding trees. At vernal equinox, the pattern would be the same as that at autumn equinox, but clearer due to bare trees. That said, it is hard to get vernal equinox pictures, since lately the weather has been cloudy, rainy, or even snowy.
       Last weekend the weather was clear, so I took  photos in the cave.  The first pattern happens around 5:43, when a thin line of light enters through the notch at the bottom left of the larger window.
Here is the thin line of light appearing inside the cave.
By 5:51 this light spread to a large triangle,
that by 5:58 spread further along the wall.
The light continued spreading, and formed the final pattern by 6:33 PM, with a point that extends to a faint mark on the wall beneath the projecting stone.
Here the mark appears  near the center of a photo taken 9/21/2012.  
     The mark looks like \ /, which could be an inverted triangle.  I have seen an inverted triangle carved into a boulder at another site with alignments (1/23/13 ).
The problem with taking photos is that I may be missing a pattern and  introducing my own shadow.  This time I tried  time-lapse photography.  I  placed the camera on the ledge on the western wall of the cave, set to take 1 frame/second with a playback of 30 frames/second.  This condensed  about 50 minutes into almost 2 minutes. The video is at Youtube here.  
      Since the camera is looking at bright spots, they appear a little burned out.  However, it is easy to see how   the point of sunlight moves across the cave wall and touches the mark at 6:39.  Since this is 10 days after equinox, the point may extend slightly beyond the mark. 
     The sun will set in the same position for August 13 at the end of April.  Maybe time-lapse will reveal more patterns at Miantonomi's Cave.

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