Box Tunnel

[daveklepper]

From Steve Sattler:

Fwd: Happy birthday to Box Tunnel and the Great Western Railway's London to Bristol Main Line, both fully opened #OnThisDay in 1841.

 

Network Rail  https://fb.watch/6s73i3cfkR/

 

 

 

[TheFlyingScotsman]

Happy birthday indeed.

I have heard that on Brunel's birthday it was aligned so that the sunrise would be visible end to end. Sadly I don't think that's true but it would be a nice touch by a great engineer.

[timz]

That's the usual story. Easy to check, if you know the grade in the tunnel. Online aerials will give the lat-lons at the tunnel ends, more than accurately enough, so you can get the tunnel's azimuth. Old almanacs are online, if you figure things have changed in the last 180 years.

[TheFlyingScotsman]

timz

That's the usual story. Easy to check, if you know the grade in the tunnel. Online aerials will give the lat-lons at the tunnel ends, more than accurately enough, so you can get the tunnel's azimuth. Old almanacs are online, if you figure things have changed in the last 180 years.

 

Thankfully the work has been done on our behalf.....

https://www.theguardian.com/technology/2017/apr/10/isambard-kingdom-brunel-birthday-box-tunnel-bath-sun

[TheFlyingScotsman]

And.............

https://www.theguardian.com/culture/2020/apr/05/new-twist-in-mystery-of-brunels-birthday-sunrise

[timz]

Turns out the tunnel azimuth at the east end is 79.57 degrees, likely error 0.1 degree or less. Grade in the tunnel is said to be 1%, so the sun's apparent altitude needs to be 0.57 degree; unrefracted altitude 0.1 degree, good a guess as any. So an object that aligns the tunnel has declination 6.56 degrees north.

In 1840 the center of the sun had that declination on the morning of 6 April; declination changes by 0.38 degree per day, so no sun thru the tunnel on 7 April 1840. Everything happens 5.8 hours later in 1841, so the sun would shine thru the tunnel on 6 April and maybe on 7 April. 5.8 hours later than that in 1842, so the sun would shine thru the tunnel on 7 April 1842, and 7 April 1843. Then resume the cycle in 1844.