Impact Theory
In certain circles, much has been made of the
theory that such large and widespread fires couldn't have
happened without assistance from an external astronomical force
-- namely,
a comet or meteor impact with the earth in the Great Lakes area.
(Commonly referred to as an "impact event.")
I am not an astronomer, but what I have seen
concerning this theory has not been very well researched or
documented. At least one proponent of this theory takes an "X-Files" approach,
citing "unexplained" phenomena and using selected facts
to draw conclusions that, while intriguing, are based more on fanciful thinking than on
science. The gullible are led to believe that the mainstream
scientific community is too lazy to pursue the "real"
cause of the fires or that some kind of
conspiracy is afoot to hide the facts from us. While
common sense points to a combination of natural and human
influences that culminated in such widespread burning, it is
apparently much more exciting for some (especially amateur
astronomers) to imagine a comet as the cause.
I understand that comet debris and meteorites
can (and do) strike the earth, and that a large impact would be
devastating. But in the end, when all the
evidence is considered, the argument for such an event as the cause of the 1871 fires becomes very
weak -- ridiculous, even.
For further discussion, see the Analysis
links to the right. Phil
Plait's Bad Astronomy site is another good source of
information. Two excellent books by reputable authors are also listed below.

DeHaan, John D. Kirk's Fire Investigation, 4th ed. Upper Saddle River,
N.J.: Prentice-Hall, 1997. [Essential for debunking the "comet" and
"spontaneous combustion of green hay" theories.]
Pyne, Stephen J. Fire in America: A Cultural History of Wildland and Rural
Fire, paperback ed. Seattle: University of Washington Press, 1997.
[Pyne
integrates the history of fire with ecology, agriculture, logging, and
resource management. He includes a vivid description of the Peshtigo fire
and the other Wisconsin fires of 1871.]