LHR-SFO in Winter - does it get dark?
Thread Starter
Join Date: Oct 2001
Location: EGKK
Age: 42
Posts: 599
Likes: 0
Received 0 Likes
on
0 Posts
LHR-SFO in Winter - does it get dark?
Quick question to the long-haulers, I noticed yesterday for example from a couple of flightplans LHR-SFO/LAX traffic was flying quite a long way north (going up to 70N ish).
At this time of year, that far north, presumably it must actually get dark at this point of the flight (over Greenland / N Canada) before getting light again as the flight heads south into the US again? Assuming a lunchtime LHR departure.
(See this World Sunlight Map).
So assuming this is the case would any pilots be able to tell me just how dark does it get, is it like a sunset for several hours or are we talking just a glow on the horizon, or complete darkness?
Thanks.
At this time of year, that far north, presumably it must actually get dark at this point of the flight (over Greenland / N Canada) before getting light again as the flight heads south into the US again? Assuming a lunchtime LHR departure.
(See this World Sunlight Map).
So assuming this is the case would any pilots be able to tell me just how dark does it get, is it like a sunset for several hours or are we talking just a glow on the horizon, or complete darkness?
Thanks.
I used to pax LHR-LAX over the years going out for Christmas, thus around this time of year (including leaving London a few hours before Pan Am 103 was destroyed in 1989 and arriving in LAX after the flight to all sorts of concerns from those back in the UK who knew me but not the detail of my plans).
Yes it does get dark in the middle of the flight, almost imperceptebly. If you leave at lunchtime it seems to get slowly dark when your body is expecting sunset by UK time, so does not seem unusual, it then very slowly gets lighter as the flight starts to dip south again. But there was always some glow in the sky to the south.
There was often the sort of red tinting of any banks of cumulus underneath that you can get at sunrise/sunset, on one trip this was spectacular and lasted for hours, from Baffin Island to beyond Winnipeg.
In the days of prop aircraft in the 1950s this was a significant difficulty for the pioneer polar flights (eg SAS DC-7C Copenhagen - Seattle - Los Angeles) as they were still reliant on astral navigation, and they spent many hours when going west with the sun just below the horizon (so no fix on it) but the sky not dark enough to see the stars. There was an instrument eventually devised to overcome this, others may have more detail.
Yes it does get dark in the middle of the flight, almost imperceptebly. If you leave at lunchtime it seems to get slowly dark when your body is expecting sunset by UK time, so does not seem unusual, it then very slowly gets lighter as the flight starts to dip south again. But there was always some glow in the sky to the south.
There was often the sort of red tinting of any banks of cumulus underneath that you can get at sunrise/sunset, on one trip this was spectacular and lasted for hours, from Baffin Island to beyond Winnipeg.
In the days of prop aircraft in the 1950s this was a significant difficulty for the pioneer polar flights (eg SAS DC-7C Copenhagen - Seattle - Los Angeles) as they were still reliant on astral navigation, and they spent many hours when going west with the sun just below the horizon (so no fix on it) but the sky not dark enough to see the stars. There was an instrument eventually devised to overcome this, others may have more detail.
Join Date: Jul 2004
Location: Sydney NSW
Posts: 513
Likes: 0
Received 0 Likes
on
0 Posts
silly me
Silly me
I suddenly remembered nav lessons flooding back!! About the sun's declination, how to estimate daylight hours
Firstly just assume that LHR is N51.5* W000.5* and SFO is N37.6* W122.4* and your apex is wpt N65* W65*
On the darkest day the sun's declination in Podea is minus 23.5 degrees. Therefore...
On the same day at N65* there is 3.5hrs "light" and at W065* it will be 1430-1800UTC. Just say it takes 4.5hrs to get there and a further 5.5hrs to reach SFO.
Same rules of thumb and SFO sunset is about 1700PST, eight hours behind UTC
I'd forgotten we had to do this once. Thank you Mr Honeywell whoever you are!
I suddenly remembered nav lessons flooding back!! About the sun's declination, how to estimate daylight hours
Firstly just assume that LHR is N51.5* W000.5* and SFO is N37.6* W122.4* and your apex is wpt N65* W65*
On the darkest day the sun's declination in Podea is minus 23.5 degrees. Therefore...
On the same day at N65* there is 3.5hrs "light" and at W065* it will be 1430-1800UTC. Just say it takes 4.5hrs to get there and a further 5.5hrs to reach SFO.
Same rules of thumb and SFO sunset is about 1700PST, eight hours behind UTC
I'd forgotten we had to do this once. Thank you Mr Honeywell whoever you are!
Join Date: Jun 2001
Posts: 324
Likes: 0
Received 0 Likes
on
0 Posts
Depends what time you get airborne, doesn't it? And how far north you go.
Departing LHR at 1130Z, it'll be daylight all the way. Depart at 1500Z (VS23 to LAX) and it'll be dark for a good proportion of the flight, though as WHBM says there's always been a glow to the south when I've been flying.
All of which leads to the interesting scenario of 2 sunrises in 1 day, the second of which sees the sun rising in the west!!
Departing LHR at 1130Z, it'll be daylight all the way. Depart at 1500Z (VS23 to LAX) and it'll be dark for a good proportion of the flight, though as WHBM says there's always been a glow to the south when I've been flying.
All of which leads to the interesting scenario of 2 sunrises in 1 day, the second of which sees the sun rising in the west!!
