[meteorite-list] Wales images: trail orientations and sun altitudes

From: Marco Langbroek <marco.langbroek_at_meteoritecentral.com>
Date: Thu Apr 22 10:28:22 2004
Message-ID: <006a01c38b6d$3406e8b0$92c1ea3e_at_HAL>

> (At 6:15pm BST, the sun was at elevation 7.8 degrees,
> azimuth 259.5 as viewed from Porthcawl.)

Rob,

This must be a mistake. The Pencoed image was taken at 7 pm (summer time) as
reported in the press (e.g. The Times, 3 October 2003,
http://www.timesonline.co.uk/newspaper/0,,174-839554,00.html), not 6 pm, the
camera header info actually gives 19:13 = 18:13 GMT/UTC for the Pencoed
image, quite in line with this.

For Porthcawl the sun was just *below* the horizon at that moment,
altitude -1d 38' ! Hence, your +7.8 degrees is certainly incorrect.

What you thought is the sun on the Porthcawl image, I reckon is the bright
glow in the downright of the Porthcawl image? This cannot be of course, as
the sun already was below the horizon. It appears to be actually sunlit
cirrus clouds. It is interesting that on this picture these appear about as
bright as the glow at the end of the discussed trail, which for the rest is
dark. If you want one clear argument in favor of this being a sun
reflection at the end of a contrail, here it is.

I would like to point out that with this sun altitude, a bolide trail should
have catched sunlight in the UPPER parts most notably. It should be the
early part of the trail which should be glowing. But this trail shows the
reverse.

On the original Pencoed image shot by Jonathan Burnett, it can be seen that
behind the dark thin cloud layer, is what must be a higher layer of thin
cloud streaks which is orange in color, i.e. is catching the rays of the
setting sun. i.e. this shows that high altitude clouds were still catching
sunlight at that time although the sun had just set (as they seem to do near
the horizon on the Porthcawl image as well, as behind an evidently lower
dark cloud layer is visible an orange-yellow illuminated higher layer). A
bolide dusttrail at above 15-20 km altitude certainly should have been
illuminated, that is, the FULL trail should, not just its end.

I also don't agree with your assessment of the angles. On the Portcawl
image, you can see that the trail comes not through the zenith, but from the
left with regard to the zenith, i.e. it is west of that location, heading
roughly east-west towards azimuth roughly 270. A site more to the east like
Pencoed, hence should have seen it slightly more from the side that
Porthcawl. i.e. under a slightly flatter angle. And that is exactly how it
is, as you pointed out. You write that "a constant-altitude contrail under
these circumstances would have to appear more steeply inclined relative to
the horizon as seen from Pencoed" but it should actually be exactly the
opposite, for a contrail being located slightly west of Portcawl. As the
part on which the Pencoed and Porthcawl images overlap evidently concerns
the part of the trail which is at some distance, the angle should not differ
too much there.

- Marco

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Marco Langbroek

marco.langbroek_at_wanadoo.nl
meteorites_at_dmsweb.org
http://home.wanadoo.nl/marco.langbroek
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Received on Sun 05 Oct 2003 02:18:42 PM PDT