June 23, 2015 at 5:46 am (physics)
Tags: lightning, Mayslake
by Carl Strang
The most dramatic event at Mayslake Forest Preserve last week came during one of the several storms that passed through the area on consecutive days. An old ash tree on the mansion grounds was struck by lightning.
The strike did not simply create a wound, it blasted out one side of the tree.
Mayslake’s site manager Janneke Waal-Fowers provides some scale as she examines the injured tree.
This example indicates why taking cover during a thunderstorm is well advised.
This heavy, pointed piece more than 15 feet long was thrown 50 feet away from the tree.
There were several pieces like this, sprayed over 180 degrees. I don’t know the exact trajectory they would have followed, but it’s all too easy to imagine a person standing in the wrong place at the wrong moment being impaled.
The tree had begun to show the effects of an emerald ash borer infestation, and a Forest Preserve District forestry crew took it down the next day. Fortunately there was no damage to the nearby Portiuncula Chapel or to First Folio Theater’s summer stage. The weddings and the shows will go on.
July 7, 2014 at 5:44 am (physics)
Tags: eclipse, light, sun dapples
by Carl Strang
Recently I noticed a patch of sun dapples on the trail, and was reminded of a surprising observation from a decade or two ago.
Notice how they all are circular in shape, with fuzzy outlines.
There was a mid-day eclipse of the sun that day, not total but the moon covered a significant percentage. I happened to be where there were patches of sun dapples like these, and as the eclipse progressed I was amazed to see the dapples changing shape. They all were images of the eclipse, at the peak showing little crescent suns.
Warnings had been broadcast in advance of the event, reminding people not to look directly at the eclipse, but to create a pinhole camera effect, holding two sheets of white cardboard, the one closer to the sun with a pinhole in it. The image of the eclipse would be formed on the back sheet, and could be sharpened by changing the distance between sheets. I realized that the tiny spaces between the leaves in the tree canopy above were, in effect, tiny pinholes, and the ground was covered by myriad images of the eclipse. The ground was not the correct distance from the canopy to produce sharp images, but they were clear enough to show the effect. The implication is that these dapples always are giving us images of the sun, as in the photo above.