The Sun Dagger at Fadaja Butte
The
famous Sun Dagger, on Fajada Butte was discovered and named by Anna Sofaer
in 1977. This phenomenon consists of a dynamic interplay of solstice and
equinox sunlight on rock petroglyphs resulting in a solar calendar. Fajada
Butte, large butte standing 135m(443 feet) above the ground at the south
entrance to the Chaco Canyon, has a series of parallel sandstone slabes
reaching 3 metres in height which serve as the stage for this performance
of light on art. On the rock cliff face is carved a large spiral petroglyph,
and next to it on the left is a smaller one which some consider a coiled
snake petroglyph. Photo
by Harrison
Lapahie Jr.
At the summer
solstice, the centre of the large spiral is bisected by a vertical shaft.
The process is as such:
- 11am local
solar time - Light spot appears above spiral, lengthening downwards
into a narrow downward pointing dagger shape of light.
- 11.05
am lst - The dagger grows and moves down as the sun moves up.
- 11.15am
lst - The dagger bisects the upper half of the spiral sharply. The overhang
above the petroglyphs casts a shadow on the slabs forming a defined
dagger shape.
- 11.18am
lst - The dagger is now moving down the lower half of the spiral without
changing shape.
- 11.20am lst - The light dagger has slipped off the cliff face.