Box Tunnel at sunrise on Brunel's birthday (9 April) - merged topics, ongoing discussion

[whole diary]

[Chris from Nailsea]

See also:

 

[grahame]

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! 

[TrainSpy]

Came across these pics - apparently from a stunt GWR^▸ (Great Western Railway) 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

[Bmblbzzz]

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.

[JayMac]

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.

[Pb_devon]

Interesting PR^▸ (Public Relations) activity by GWR^▸ (Great Western Railway):

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.

[Rob on the hill]

Some impressive pictures from GWR^▸ (Great Western Railway)'s Facebook page:
https://www.facebook.com/gwruk/posts/10154346578721806

[Oxonhutch]

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.

[stuving]

Now, exactly what would you see if the light did get right through the tunnel? The sun's width is 0.53^o (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 0.15^o 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 0.62^o 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 1.4^o, 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 (-0.57^o) plus the effect of refraction (-0.57^o) and either the look-down from your eye height (-0.03^o) and down half the Sun's width (-0.27^o) or the height of the portal (+0.16^o, based on 8 m) and up half the Sun's width (+0.27^o) if you crouch right down: -1.44^o to -0.71^o. 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 79.36^o plus or minus the tunnel width (0.16^o if you can move to the sides) and the Sun's width (0.27^o): 78.94^o to 79.78^o.

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

Wikipedia reports it did happen on April 5th in 1992:  I get it at 79.17^o azimuth (pretty central) at -0.7^o elevation, and going out of the side at -0.9^o. 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.

[JayMac]

Well, with those last two posts I've been blinded by the maths, rather than the sun! 

[Chris from Nailsea]

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

[ChrisB]

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

[Madinventor]

Please can I add some information to your discussion
The sun will not shine through the IKB^▸ (Isambard Kingdom Brunel)’s Box tunnel not on the 5th, 6th, 7th, 8th, 9th or 10th of April or the September equivalent not at the moment anyway.
Several things conspire to stop this from happening.
The 6.00am train from Bristol fills the tunnel with diesel fumes before sunrise, recent electrification might soon resolve this first problem.
The south embankment does cover a portion of the tunnel’s eastern portal, when viewed from the western side, it obstructs from the bottom left corner diagonally up at about 45° to the point where the roof curve meets the top of the right hand tunnel wall.
At the moment there is also very tall shrubs and trees on this embankment which blocks the rest of the tunnel’s alignment out completely.
So recent investigations by the GWR^▸ (Great Western Railway) engineers in 2017 was always going to fail to prove this so called “myth” really works.
The next problem is the English morning weather, how many April days have zero cloud or mist between Bath and Reading at 06.30 am ?
I took a picture on the 9th of April 1982 of the sun shining down the tunnel or at least as good as it ever will on the 9th of April. This photo was the cover photo for the New Civil Engineers investigation 4th April 1984 p. 29 - 31
Why did I get a picture of the sun illuminating the tunnel brightly and the the reflection bouncing off all four rails, here is the reasons…
Recently before 1982 (don’t know the exact year) the eastern south embankment was cleared of all shrubbery and trees.
1982 was a Bank Holiday so there was no 06.00 am train out of Bristol, the best image was taken at about 06.44 am, in those days you were limited to 24 colour shots using a Practica SLR 35 camera.
It was the clearest night I ever saw when driving to Box, which I did from 1977 until 1985. After which I realised I would never see the sun shine through it again so stopped visiting the area.
Also it was different times when it comes to safety, annually up to 20 people would be on the tracks with genuine interest and so would GWR staff assisting us and allowing us to be there, after 1983 the rail staff were only there to keep us out of railway property.
By the way only me and a guy from Birmingham driving a 2CV were there on the 9th April in 1982.
I do believe that a better date is the 6th or 7th April (which all mathematical calculations confirm) and why I think this is,  there is a picture taken by Jim Barnes in 1985 a year where the shrubbery was still low on the east south embankment allowing you to see what is clearly the sun within the Eastern portal. If the 6.00 am train from Bristol had not filled the tunnel with fumes 10 minutes before he took that picture that would be the most stunning proof and I doubt if you would have been able to look up the tunnel at the sun with the naked eye without hurting your eyes. That sun is penetrating through 2 miles of confined diesel fumes.
So don’t rush off trying to see this phenomenon, not until the trees are cleared, 100% of trains are electric using the line or it has to be a Bank Holiday, you need one of the best clear nights prior to “the 6th or 7th of April” and permission from Network Rail or GWR, and a key to the Western access gate.
Sorry to disappoint you all and unless you are very very young now you have no chance of seeing IKB’s genius creation as intended, they will cut the trees again but not until they are big and old enough to cause a danger to the trains.

Regards   david@needhams.uk.com, Chesterfield

[Chris from Nailsea]

Wow! 

Thank you very much for that fascinating post, Madinventor - and may I offer you a very warm welcome to the Coffee Shop forum.

Are any of those pictures already available for us to view, anywhere on the internet - or are you possibly able to give us any links to them here?

[Madinventor]

Chris,
Thanks for the response and continued interest
I do need to make a couple of corrections,
Firstly, the New Civil Engineer investigation was the 4th April 1985 not 1984
Secondly, my photo was not the cover photo but the article photo on page 31
I looked for the photographs today, and failed to find them but I did find the negatives, herewith a link to a previous posting of my photograph
https://www.flickr.com/photos/28512889@N05/24777797845/
or put in to Google “David Needham Box Tunnel”
I do have a copy of the 4th April 1985 New Civil Engineer though posting it would and could infringe their copyright and I would need express permission from Metropolis International Ltd the current owners of the title.
Looking at the web photo which is nowhere near as clear as the actual Number 13 picture that was originally printed, it is today clear to me that the sun was close but not perfectly aligned on the 9th of April, it was just a very clear a day and a clean tunnel which makes my photograph definitely the best April the 9th picture and probably as good a picture as has ever been taken from the western end of the sun at the eastern end.
My view always was that if you can see the sky from the western end looking east at some point the sun’s travels across our sky must pass the point of the tunnel alignment.
Today's issue is the sky is not visible through the tunnel as per my previous post.