Stop & Examine
Brunel’s Box Tunnel.
Our recent article about Box Tunnel ( RAIL 825), and whether Brunel’s design featured a special personal birthday present, certainly aroused the interest of RAIL readers.
It is one of the railway’s greatest myths: did the engineer design the Tunnel so that the sun shines directly through the structure on his birthday - April 9?
And we’ve had some illuminating responses.
Brian Rice, from Horsham, takes issue with a comment from Great Western Railway Commerical Development Director Matthew Golton, who had told RAIL: “Given that the sun rises in a slightly different spot from the east each day, it’s hard to predict the days with pinpoint accuracy.”
Says Brian: “Those with the correct training can readily calculate the azimuth (the horizontal angle measured from north) of any star, including our sun, or planet for any time of any day, while the whole point of leap years is to keep our Gregorian calendar aligned with the exact rotation of the sun.
“It drifts slightly each year but inserting one more day every fourth year largely corrects this.”
Martin Rickman, from Yaxley, has gone into even greater detail:
“Man has been using the sun and the stars for surveying and navigation for thousands of years,” he tells us.
“The ancient Egyptians built the Pyramids with precise positions and alignments, and the Celts and others did the same with their stone circles - including Stonehenge, which has more astronomical alignments than just mid-summer sunrise.
“Even then, they understood the procession of the equinoxes, which is the apparent rotation of the heavens over a period of approximately 26,000 years.
“We can now predict with absolute accuracy the times of the various solar and lunar eclipses, and Brunel had the necessary information to align Box Tunnel to the sun on his birthday.
“He needed to know the position of the rising sun at a particular time on the morning of April 9, as he had to calculate the tunnel alignment in three dimensions. Not only must the horizontal alignment be correct, but also the rising gradient of the tracks to the east.
“Brunel’s solution was not perfect and cannot be so, because the position of the rising sun on the morning of April 9 varies from year to year.
“Pope Gregory XIII introduced the Gregorian calendar in 1582, and it included an extra day each leap year to minimise the difference between the solar cycle of 24-hour days and the astronomical year of 365 days 5 hours 49 minutes 12 seconds. The leap years are omitted each century, unless they can be divided by 400 - so the year 1600 was a leap year (as was 2000), but 1900 was not and nor will 2100 be.
“Because of this, the path of the rising sun on April 9 moves slightly further to the south each year, until each leap year when it appears to ‘jump back’ to the north. I cannot tell you on which years the sun will shine right though Box Tunnel, but I am sure if Network Rail were to allow access to their 3D co-ordinate data then this could be calculated?”
“The same alignment re- occurs on September 2, as the sun retreats to the south on the far side of the Summer Solstice.”
Phew! So there you have it! Wonder what Professor Brian Cox would make of that?