Darkness at Noon

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NickFaulks
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Darkness at Noon

Post by NickFaulks » Fri Aug 12, 2022 9:53 am

My flight back from Chennai on Wednesday, BA 36 direct to London, was the weirdest I have ever had.

We took off at 5.45, around sunrise. The sun was directly behind us so I never saw it, but for a while the light got brighter as you would expect, then it started getting darker until after an hour it was pitch dark, just like a normal night flight. This continued for five hours, until somewhere over Romania daylight abrupted returned, with the sun where you would expect.

I had the flight information screen on throughout and took some photos. According to that, we passed over Dubai at about 10am local time. Their weather records show a clear sunny day, but out of the plane window was complete darkness.

I cannot think of an explanation that does not sound like one of the more far out X-Files plots. Any ideas? Any pilots, or people who know pilots?
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AlanLlewellyn
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Re: Darkness at Noon

Post by AlanLlewellyn » Fri Aug 12, 2022 11:12 am

its an effect known in aviation as the dark side of the moon effect LOL just joking, the speed the earth goes around from west to east probably was less than the speed you travelled east to west, i am not sure of the speed but that affected it you would have travelled 900 km/h the 8000 km or so distance(guessing with figures), look up the speed of rotation.

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AlanLlewellyn
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Re: Darkness at Noon

Post by AlanLlewellyn » Fri Aug 12, 2022 11:15 am

plus their is the latitude effect in that the sun rises earlier in the equatorial regions than it does at our high latitude.

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Christopher Kreuzer
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Re: Darkness at Noon

Post by Christopher Kreuzer » Fri Aug 12, 2022 7:27 pm

NickFaulks wrote:
Fri Aug 12, 2022 9:53 am
My flight back from Chennai on Wednesday, BA 36 direct to London, was the weirdest I have ever had.

We took off at 5.45, around sunrise. The sun was directly behind us so I never saw it, but for a while the light got brighter as you would expect, then it started getting darker until after an hour it was pitch dark, just like a normal night flight. This continued for five hours, until somewhere over Romania daylight abrupted returned, with the sun where you would expect.

I had the flight information screen on throughout and took some photos. According to that, we passed over Dubai at about 10am local time. Their weather records show a clear sunny day, but out of the plane window was complete darkness.

I cannot think of an explanation that does not sound like one of the more far out X-Files plots. Any ideas? Any pilots, or people who know pilots?
It sounds like the cause of this is the take-off being at around sunrise. Remember that as the plane gains altitude, you will be ahead or behind the 'solar' time on the ground. Also remember that the Earth rotates east-to-west and you are flying west-to-east (and also to the north as well, which also helps produce this effect). Presumably the initial trajectory of the plane was such that the Earth's rotation was slower than the east-west component of the flight trajectory, hence the light getting brighter. The getting darker bit might be the plane at its cruising speed getting ahead of the Sun and staying in the shadow of the Earth (i.e. night-time). Except I shouldn't say ahead of the Sun, it is more keeping up with the Earth's rotation.

It is probably easier to think of the day-night terminator as an object moving at a set speed, and consider how the plane keeps up with, or falls behind that dividing line. Adjusting for the fact that you are at altitude. Also remember that you can be very close to the 'sunrise' point when at high altitude, and it can still be very dark. As you found, sunrise is very rapid at that altitude and moving at that speed. Hence the abrupt return of sunlight over Romania. Sunrise is 'slower' (for want of a better word) when it occurs at the surface.

I suppose I'd better check I got this right!

Strangely, I couldn't find anything obvious on a quick search. Surely this has been written about. People have written about how it is possible to see the sun rise in the West when flying east-to-west. But that is on supersonic flights that take off after sunset. Subsonic flights taking off at sunrise will fall behind the sunrise and fall back into the night. What is a bit strange in your case is the timing being just right to have brightening first, then darkness, then sunrise again.

I would hazard a guess the plane may have changed trajectory and speed a fair amount. Was it taking a big loop around the closed airspace due to the Ukraine-Russia conflict maybe? That must be it! :shock: (If you can remember the route the plane took and when you were travelling more west than north (and vice-versa), and what direction the plane was travelling in when the sunlight returned over Romania, that would help.)

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AlanLlewellyn
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Re: Darkness at Noon

Post by AlanLlewellyn » Fri Aug 12, 2022 8:10 pm

christopher just repeat exactly what i said in longer words why dont you? i am glad i am not being ignored or anything.

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Christopher Kreuzer
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Re: Darkness at Noon

Post by Christopher Kreuzer » Fri Aug 12, 2022 8:30 pm

AlanLlewellyn wrote:
Fri Aug 12, 2022 8:10 pm
christopher just repeat exactly what i said in longer words why dont you? i am glad i am not being ignored or anything.
Diagrams, we need diagrams! :D

Seriously, sorry if it looked like I was ignoring you, I got a bit carried away trying to put the mechanics of it into words. It is essentially the same as what you said, with a titchy tiny bit more added. Did you have to look up the speed of a commercial airliner, or did you know that already? You are right, someone needs to look up the speed of rotation of the Earth. It would be the distance of the circumference divided by 24 hours. So what is the speed of rotation of the Earth at the poles? :twisted:

David Williams
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Re: Darkness at Noon

Post by David Williams » Fri Aug 12, 2022 9:07 pm

I have no explanation, I wouldn't have thought you could outrun the sun at those latitudes. The best I can suggest is that in summer the further north you are the longer the daylight hours, and the first part of your journey heads south of west. Dubai will have a shorter day than Chennai.

Your timings seem to be questionable.

10:00 local time in Dubai is 11:30 in Chennai, so 5 hours 45 minutes after you took off. And you were over Romania 15 minutes later?

Google gives a flight time of 4 hours 30 minutes from Chennai to Dubai, and 5 hours from Dubai to Bucharest.

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AlanLlewellyn
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Re: Darkness at Noon

Post by AlanLlewellyn » Fri Aug 12, 2022 9:56 pm

the speed of a plane has remained constant for such long journeys at around 900 km/h the sun moves at a constant rate of around 800 km/h as seen by the size of most time zones (split into 24 hourly slots and about 800 km long) so yes a plane can go faster than the sun

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AlanLlewellyn
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Re: Darkness at Noon

Post by AlanLlewellyn » Fri Aug 12, 2022 10:03 pm

latitude is not height david and you didnt answer whether you were the same david williams i met at blackpool congress from cardiff i assume youre not from youre lack of response

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AlanLlewellyn
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Re: Darkness at Noon

Post by AlanLlewellyn » Fri Aug 12, 2022 10:04 pm

latitude is distance away from the equator

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JustinHorton
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Re: Darkness at Noon

Post by JustinHorton » Fri Aug 12, 2022 10:28 pm

By the way if you haven't read it Koestler's novel is great stuff
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David Williams
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Re: Darkness at Noon

Post by David Williams » Fri Aug 12, 2022 11:37 pm

The circumference of the earth is 40,000 km. At the equator a plane would have to travel at nearly 1700 km an hour to race the sun. At, say, 30 degrees north it's still going to require the plane to be going 1500 km an hour or so. The radius of the earth is 6400 km. The fact that a plane is 10 km higher than this makes virtually no difference. I've never been to the Blackpool congress.

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AlanLlewellyn
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Re: Darkness at Noon

Post by AlanLlewellyn » Sat Aug 13, 2022 4:55 am

this is the player i meant simon williams not david sorry david for confusion. here is the game which i played against him in 2018

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AlanLlewellyn
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Re: Darkness at Noon

Post by AlanLlewellyn » Sat Aug 13, 2022 5:01 am

as can be seen from above game Simon has nine lives or maybe more

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Christopher Kreuzer
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Re: Darkness at Noon

Post by Christopher Kreuzer » Sat Aug 13, 2022 9:55 am

David Williams wrote:
Fri Aug 12, 2022 11:37 pm
The circumference of the earth is 40,000 km. At the equator a plane would have to travel at nearly 1700 km an hour to race the sun. At, say, 30 degrees north it's still going to require the plane to be going 1500 km an hour or so. The radius of the earth is 6400 km. The fact that a plane is 10 km higher than this makes virtually no difference. I've never been to the Blackpool congress.
There is a misunderstanding here. Racing the sun is what happens when taking off after sunset when flying west towards the recently set Sun and trying to get back into the daylight. That was possible with Concorde.

But the situation Nick described is a plane taking off after sunrise and flying west, though my suspicion is that the plane was actually flying north, south and maybe briefly east as well at various points. It also sounds from what others have said that Nick has some of his timings wrong.

The 10 kilometres of altitude will make a difference to the timings and the geometry with respect to the Earth's shadow. It is possible for it to be dark 10 km up and daylight on the ground below.

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