[meteorite-list] Wales contrail

From: Matson, Robert <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Thu Apr 22 10:28:22 2004
Message-ID: <AF564D2B9D91D411B9FE00508BF1C86901B4EDD4_at_US-Torrance.mail.saic.com>

Hi Bj=F8rn and List,

Just a few comments in response to some of your questions/remarks:

> Marco comments that the trail behind the head should be sunlit since
> it must be higher in the sky. Some points why it might still not
> appear sunlit:

> a) As the trail is further east, the sun sets earlier is this
> direction, so the sun may have set from this point, or be obscured
> by clouds on the horizon, which we onbserve there are, certainly.
> This even though its probably great height.

No, you are incorrect here. From an altitude of only 20 km, the
elevation angle of the sun relative to the horizon increases by
some 4 1/2 degrees; from 30 km altitude it's over 5 1/2 degrees.
None of the clouds in the scene could have occulted the sun from
that vantage point.

> Rob, how you suddenly today came down from a high trajectory to
> 10k, I don't really understand?? Just because Marco said the sun
> was 1 hour further on in azimuth?

Yes -- that's all it takes. The angles are critical here -- not
just the azimuth but the elevation angle. That elevation angle
was based on my assumption that the sun was in the field of view
(behind clouds), which itself was based on the erroneous 6 pm
figure posted on the Planetary Society's website. (I'd like to
thank them personally for wasting three hours of my time!) With
the later time for the images, the sun's location moves just below
the horizon and 11.5 degrees further to the right. The vanishing
point moves to a little greater than 260 degrees, now exceeding
the critical 255-degree point. Because of the comparatively
large difference in angles between the trajectory and the horizon
as seen from two points just ~10 miles apart, all solutions require
a nearby object -- which in turn means a low altitude one.

Using the old image time assumptions, the vanishing point was at
an azimuth less than 255 degrees, and by similar arguments it
could not be satisfied by an object in level flight.

> One IMPORTANT thing I found today is this: The cloud formation
> in the Pencoed 1ST image and the Porthcawl image have INDENTICAL
> form and placement.

Believe me, this was helpful because the relative placement of clouds
in the two images could be used to correctly orient the Pencoed
image (which is tilted).

> Some solutions:
> 1) The two observers are on the exact same line of sight.

It's not the exact same line of sight to the terminus, but pretty
close.

> Not really possible as the object have some height in the sky,
> and Jonathan is probably higher up in the terrain than Julian.

The small difference in altitudes between the two observers is
completely unimportant. Also, there is absolutely no way to
accurately judge the elevation angle in the Pencoed image because
the horizon is not visible.

> The different steepness of the tail also counter this.

The different steepnesses of the tail coupled with the sighting
line to the west-southwest are what kill a high-altitude solution.
For a high altitude object, the tail slopes would have been nearly
the same.

Best,
Rob
Received on Sun 05 Oct 2003 08:25:24 PM PDT