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Author Topic: Box Tunnel at sunrise on Brunel's birthday (9 April) - merged topics, ongoing discussion  (Read 8241 times)
Chris from Nailsea
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« Reply #15 on: April 10, 2017, 12:32:39 AM »

See also:


 Grin

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William Huskisson MP was the first person to be killed by a train while crossing the tracks, in 1830.  Many more have died in the same way since then.  Don't take a chance: stop, look, listen.

"Level crossings are safe, unless they are used in an unsafe manner."  Discuss.
grahame
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« Reply #16 on: April 10, 2017, 08:01:33 PM »

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

Which (as far as I can tell as I'm on an icky connection) looks far better.  Excellent sources recommend it, anyway!  Grin
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TrainSpy
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« Reply #17 on: April 10, 2017, 08:11:04 PM »

Came across these pics - apparently from a stunt GWR did at the weekend. Wondered if anyone here had seen any more kicking around - can't seem to hunt any more down...

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

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Bmblbzzz
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« Reply #18 on: April 10, 2017, 10:35:25 PM »

That Guardian article is not quite convincing. It's as if they really wanted to believe the legend but couldn't quite make the facts fit. They quote someone who was at the eastern portal saying that the sun was shining down the tunnel but they couldn't see how far. But the people at the western end weren't seeing the sun shine directly through the tunnel. Well, at the eastern end the sun is always going to be shining somewhat into the tunnel when it rises. If it was really aligned 'correctly' then you'd be able to see the sun rise from the western end too. Of course it's always possible Brunel aligned it with the setting sun, but they don't seem to have tested it in the evening.
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Day return to Infinity, please.
bignosemac
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« Reply #19 on: April 10, 2017, 11:30:45 PM »

A pleasing coincidence, nothing more.

Brunel designed the tunnel using his engineering skills, his knowledge of geological conditions, the necessary alignment, and his tunneling experience. To suggest he chose the alignment to match sunrise on his birthday is just fanciful revisionism.
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Pb_devon
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« Reply #20 on: April 11, 2017, 08:28:13 AM »

Interesting PR activity by GWR:

https://www.gwr.com/about-us/media-centre/news/2017/april/gwr-proves-brunels-sunshine-theory-is-there-light-at-the-end-of-brunels-box-tunnel

I guess the wires will prevent that view in future, so an excellent opportunity taken.
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Rob on the hill
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« Reply #21 on: April 11, 2017, 10:02:48 AM »

Some impressive pictures from GWR's Facebook page:
https://www.facebook.com/gwruk/posts/10154346578721806
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Oxonhutch
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« Reply #22 on: April 11, 2017, 10:19:56 AM »

An interesting one. For an engineer of his age, I could well believe that he might have been tempted to assert his mathematical prowess if the deviation from the ideal was of little to no consequence to the final outcome.  Victorian engineering and art are rarely separated. The challenge for me though is to calculate the sun’s position at the crack of dawn on 9th April 1806 at the western mouth of Box Tunnel. I am sure it can be done – the ancients building Stonehenge apparently managed it!

I have checked on the SunCalc website and this year’s alignment did not add up.  I do not have enough nous though to vet their calculation. I couldn’t get it to give me a sun rise in 1806.

Figure 1: http://suncalc.net/#/51.4174,-2.2603,14/2017.04.09/09:27

The big question though is the distribution of leap years with the complication that 2000 was a leap year – normal centuries are not!
The distribution of the summer solstice from Wikipedia show this well and there will be a similar effect on the direction of the rising sun.
 
Figure 2: Modified after https://en.wikipedia.org/wiki/Leap_year

As a geologist, I am aware that the Atlantic Ocean is up to 10 metres wider today than at Brunel’s birth and that the Greenwich Meridian has varied though time against WGS84. Further more, with Euler rotations of continental plates through time, even north itself is a variable feast.
« Last Edit: April 11, 2017, 10:34:48 AM by Oxonhutch » Logged
stuving
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« Reply #23 on: April 11, 2017, 08:25:39 PM »

Now, exactly what would you see if the light did get right through the tunnel? The sun's width is 0.53o (31'), and the tunnel is 2930 m long. I'm not sure of its width, but I've guessed at 8 m, so the far portal would appear as 0.15o wide. So those pictures of a little Sun framed in the portal were taken just a few steps into the tunnel - from the far end, you see a gleam that might be tunnel-shaped, certainly not roundly Sun-shaped.

I found an Excel workbook with the sums included as VBA, which seems to be pretty reliable. On the other hand, some of the numbers I've assumed have an distinct odour of damp finger about them. If you know better, do say.

First note that the azimuth of sunrise, however defined, moves at about 0.62o per day near the equinox. The calendar and varying synchronisation of the Earth's spin with sunrise moves the position over a total range of about 1.4o, but the formulas know about that. But that does mean that the just-risen Sun overlaps its position yesterday just a little, giving you a day's wiggle room.

Now the range of elevations at which you could see Sun down the tunnel is the gradient (-0.57o) plus the effect of refraction (-0.57o) and either the look-down from your eye height (-0.03o) and down half the Sun's width (-0.27o) or the height of the portal (+0.16o, based on 8 m) and up half the Sun's width (+0.27o) if you crouch right down: -1.44o to -0.71o. Refraction does vary a bit around that average value.

At an elevation within that range, the sun has to be at the right azimuth. I have that as 79.36o plus or minus the tunnel width (0.16o if you can move to the sides) and the Sun's width (0.27o): 78.94o to 79.78o.

This year, on the 9th, at -0.7o elevation the azimuth is 76.77o - out of sight. It is in the azimuth range at elevations of +1o or more - out of sight uptheway.

Wikipedia reports it did happen on April 5th in 1992:  I get it at 79.17o azimuth (pretty central) at -0.7o elevation, and going out of the side at -0.9o. That has a fair chance it would be visible.

Note that even a rough surface reflects much better than you'd expect if light falls on it at a very shallow angle. Being damp would also help a lot. So you might see a bit, even if the Sun is strictly out of sight. Of course if you'd never seen the "real" thing, you wouldn't know that wasn't it.
« Last Edit: April 11, 2017, 09:59:35 PM by stuving » Logged
bignosemac
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« Reply #24 on: April 11, 2017, 09:01:21 PM »

Well, with those last two posts I've been blinded by the maths, rather than the sun!  Grin
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Chris from Nailsea
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« Reply #25 on: April 11, 2017, 09:56:23 PM »

... whereas Brunel himself probably just scribbled his workings out on the back of a cigar packet ...  Wink Cheesy Grin

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William Huskisson MP was the first person to be killed by a train while crossing the tracks, in 1830.  Many more have died in the same way since then.  Don't take a chance: stop, look, listen.

"Level crossings are safe, unless they are used in an unsafe manner."  Discuss.
ChrisB
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« Reply #26 on: April 12, 2017, 10:01:49 AM »

Saw photos taken by Matthew Golton yesterday from the Eastern end at sunrise, and yes, light from it could be seen through the tunnel at the western end....was quite impressive
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