" is the answer I give students after asking them, "When is a shadow not a shadow?" Shadow bands
are alternations of light and dark that glide across the landscape; they're caused by the crescent Sun, or its cusp points, twinkling.
Apart from a poor 1925 image, by the 1970s better film emulsions did on occasion record shadow bands
. Today's digital cameras are much better than film at discriminating low-contrast bands on a smooth white screen--a project worth considering on August 21st, when the first total-solar-eclipse track in 99 years sweeps the contiguous U.S.
In fact, the cloud provided a thin projection screen so we again recorded shadow bands
in the sky although these were not as prominent as at the South Pacific eclipse of 2010.
seen on the clouds of the 2010 total solar eclipse
Others spotted shadow bands
dancing irregularly on the ground a minute or two before totality, their visibility enhanced on the snow.
The 1970s brought further developments such as the building of an observatory, the purchase of a DayStar 0.65A hydrogen-alpha filter and a trip to Zanzibar in 1976 to study shadow bands
during the total eclipse of the Sun.
I was interested to see the article by Nick James in the October Journal (JBAA, 120(5), p.317) reporting imaging of shadow bands
on thin cloud during the 2010 total solar eclipse.
I explained about the approaching shadow, falling temperature, shadow bands
, the chromosphere and corona, planets and stars to look for, and so forth.
can occasionally be seen as faint, rippling waves on the ground just before 2nd and just after 3rd contact.
are among the most elusive of all eclipse phenomena.
rippled across the sand for ten or twenty seconds before second contact, wider, darker and more sharply defined than those in Libya in 2006.
Observers in Libya and Turkey reported prolonged and obvious shadow bands
. Jim Rosenstock and David Weber described the display in Jalu as "awesome," as if they and their fellow observers were "standing in a river of shadow bands