>This conversation reminded me of a claim made for the Box Tunnel on the
>Great Western Railway, England. It is said that on one day of the year
the
>sun can shine through the tunnel. It is also said that the day on which
this
>happens is Isambard Kingdom Brunel's birthday. He was the guy that
>designed and built the tunnel.
>
>Is this story apocraphal, or is there some truth in it? Does anyone know?
The sun can indeed shine through Box Tunnel tantalisingly close to Brunel's
birthday on 9th April.
The tunnel azimuth is some 79d 35' and the track has a gradient of 1 in 100
rising to the east (altitude 34'). The far opening subtends a vertical
angle of 0.21d from the other end - the corresponding horizontal angle is
0.18d.
The tunnel was designed in the early 1830s and for 1835 we have:
Date time (UT) solar azimuth solar altitude
(corrected for
refraction)
April 7 05.35 79d 16' 0d 21'
05.40 79 38 0 37'
April 8 05.38 79 05' 0 39'
05.40 79 28 0 55
April 9 05.35 78 19' 0 35'
05.37 78 42 0 48'
Taking into account the sun's angular diameter, sunlight passed directly
through the tunnel on 7th April but not on Brunel's birthday.
The sun is nonetheless reported to shine through on his birthday and there
is at least one photograph showing a bright spot at the far end. The
alignment is so close that the bright light of a clear sunrise could give
that appearance.
Brunel certainly had the means and ability to make the necessary slight
changes in alignment to thus illuminate his birthday. It appears that he
did not. Perhaps the tunnel and the Great Western Railway were already a
sufficient monument.
Les Cowley
[EMAIL PROTECTED]
