High Altitude Triangular Cloud Report

Around 0130 UT 15 Feb 2004 at latitude 41 48 08 N, longitude 94 37 53 W I
observed a triangular white cloud about 1 to 2 degrees wide centered over
Omicron 1 & Omicron 2 Eridani. The sky was completely clear, except for this
anomalous cloud. I was observing from a very dark location about 10 minutes
after the end of astronomical twilight, and this cloud had a high enough
surface brightness that I am certain it was not being significantly illuminated
by terrestrial light sources.

The cloud had a diffuse edge, and had no discernable color other than white. I
was able to observe the cloud for nearly 40 minutes, during which time it
isotropically expanded and dimmed. The expanding cloud moved very slowly
relative to the background stars, so that right before it faded to invisibility
(40 minutes after I first saw it), it was only about 5 - 10 degrees southwest
of Omicron 1 & Omicron 2 Eridani. There was no detectable fluctuation in
brightness as is usually seen with isolated auroral clouds, only a slow dimming
as it expanded.

I have seen this phenomena twice befo once in the late 1990s (in June at
Jefferson, Iowa), and once in 1980 At Iowa State University's Erwin W. Fick
Observatory near Boone, Iowa. The former was a circular cloud, and the latter
was a cloud about 6 degrees long and about 1 degree wide.

Does anyone have an explanation for this phenomenon? Have any of you observed
similar events?

Thank you,

David Oesper
Ames, Iowa