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

From: Matson, Robert <ROBERT.D.MATSON_at_meteoritecentral.com>
Date: Thu Apr 22 10:28:22 2004
Message-ID: <AF564D2B9D91D411B9FE00508BF1C86901B4EDD2_at_US-Torrance.mail.saic.com>

Hi Marco and List,

Earlier I wrote, in part:

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

Marco replied:

> 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.

The only reference to the time I found was on the Planetary Society's
website, which said the image was taken around 6 pm:

<http://planetary.org/html/news/articlearchive/headlines/2003/meteors_galore
.html >

It was based on this report that I assumed that I was seeing
the sun in the lower right of the Porthcawl image. Just goes to
show you can't believe everything you read. Obviously my analysis
dependends entirely on an accurate position for the sun, and if
what you say is true, I now don't have one. I suppose I can still
estimate the sun's position below the horizon in the Porthcawl
cell-phone-camera image, and from this estimate other azimuths
in the image. If the image was taken, for instance, at 7:13pm BST,
the sun was at azimuth 270.9, elevation -0.8 deg as seen from
Porthcawl (51.4769 N, 3.7078 W) -- in other words, just a couple
minutes after sunset.

> 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.

Yes, this is a VERY good point. If this is a bolide, and the
end is sunlit, the entire track should be sunlit! I don't know
why this didn't occur to me earlier. The only tracks that won't
be completely sunlit are low-altitude ones of flat trajectories --
in other words, aircraft contrails.

> 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.

Actually, the vanishing point for the track is toward an azimuth
somewhat south of the due west, so it cannot be an east-west
trajectory -- it must be somewhat east-northeast to west-southwest.
If the true track heading is any further south than about azimuth
255, then the same track as viewed from Pencoed must be steeper,
since the azimuth of Porthcawl as seen from Pencoed is 255. The
fact that the Pencoed track is slightly flatter means a level-flight
contrail must have an azimuth somewhere between 255 and ~265.
Pretty tight constraint. I'll rerun the numbers and see what
sort of altitude solution I get.

--Rob
Received on Sun 05 Oct 2003 03:42:50 PM PDT