From: Mike Lorrey (mlorrey@datamann.com)
Date: Sun Jun 16 2002 - 17:19:13 MDT
spike66 wrote:
> About 10 seconds after I noticed the
> shadow, I was able to spot a plane, which I was able
> to identify as a 747, headed for landing at San Francisco.
> It surprised me that the plane was so difficult to spot
> even tho I knew about where it had to be. There was
> no noise, no contrail, just a silver plane against a blue
> sky. I would never have spotted it without the additional
> information provided by the shadow.
>
> I think a 747 is about 70 meters in length, so if it were
> on approach, 7 km altitude, its fusilage would span the
> apparent diameter of the sun. An observer directly in
> the path of that shadow would see the sun about 30%
> eclipsed, were she able to snap a photo just as the
> plane passed in front of the sun.
>
> Mike, could the shadow you saw have been caused by
> a 747 on approach to landing in New York?
Well, I thought of that, and I've got pretty good eyesight at distance,
but I didn't notice anything. I'm pretty good at spotting high altitude
planes like Air Force tankers, and they generally sport contrails if
they are so high as to be nearly indistinguishable, but I can still spot
those. I also thought that the shadow was way too big to be made by a
mere aircraft, as it was something like 1-2 km wide, at least. I have
also seen aircraft shadows pass by, and they certainly have a
distinguishable cross-like shape. I suppose that the Concorde wouldn't
make that sort of shape, and it flies into New York from europe through
our airspace, following a 'great circle' course, but I don't see how
it's shadow would be that wide.
How high do blimps fly? Can they fly in the jet stream?
If it wasn't a blimp or the Concorde, I'm still leaning toward an earth
crossing asteroid. It was going too fast, I think, to be a blimp. It was
going 1/2 to 1 mile a second in speed along the ground, which the
Concorde could do easy. If a NEA were passing at an oblique angle to our
planet's orbit, it's shadow would travel that slow, as it would at any
point in it's orbit within the earth's path if its orbit was half in and
half out of ours.
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