Speed of the Sun
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Speed of the Sun
There is a thread (silly one, at that) on JB about whether the Earth is round or flat? That thread and a late day flight from SVO the other day got me to thinking. What is the formula for the speed of the sun as it transverses the Earth, or more accurately, how does one calculate the apparent motion of the sun accounting for higher latitudes and altitudes? I know the apparent motion is slower with both.
GF
GF
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Attempted solution..
I'll give it a shot...
The sun moves at an apparent 15 degrees per hour...111 km (59.9 nm) times the cosine of the latitude, should give you the apparent distance per hour and thus apparent speed, right? I guess for altitude effects you would need to account for the increased dimension of the radius between Earth's axis and the A/C.
This reminds me of something interesting. I either read or was told in a lecture given by a former SR-71 pilot (can't recall which at the moment), that said pilots were the only aircrew to see the sun "rise" in the west. I never put any math to it but it sounds believable.
The sun moves at an apparent 15 degrees per hour...111 km (59.9 nm) times the cosine of the latitude, should give you the apparent distance per hour and thus apparent speed, right? I guess for altitude effects you would need to account for the increased dimension of the radius between Earth's axis and the A/C.
This reminds me of something interesting. I either read or was told in a lecture given by a former SR-71 pilot (can't recall which at the moment), that said pilots were the only aircrew to see the sun "rise" in the west. I never put any math to it but it sounds believable.
Thread Starter
Thanks, FlyVMO! I guessed the cosine bit and found the velocity of the earth is 903 knots, but the effect of altitude is still a mystery.
Not true that the SR-71 could make the sun rise in the west and set in the east--the Concorde could do it also. In fact, any plane flying greater than 903 knots (x the cosine of it latitude) for ground speed long enough could do it. We were SVO-EWR and at 61 degrees north with a 440 or so ground speed, the sun sat just below the apparent horizon for about 7 hours. FL 470.
GF
Not true that the SR-71 could make the sun rise in the west and set in the east--the Concorde could do it also. In fact, any plane flying greater than 903 knots (x the cosine of it latitude) for ground speed long enough could do it. We were SVO-EWR and at 61 degrees north with a 440 or so ground speed, the sun sat just below the apparent horizon for about 7 hours. FL 470.
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A question I have always wondered :-
If you are heading west, what speed would you have to be travelling at to have the earth rotate beneath you whilst you remained stationary relative to the moving earth. Basically you take off and climb, then the earth rotates around beneath you until your destination arrives, then you decend and land.
Not sure I made that sound too clear but it's just one of those "always wondered" questions I have had and the ATPL notes don't really cover it.
If you are heading west, what speed would you have to be travelling at to have the earth rotate beneath you whilst you remained stationary relative to the moving earth. Basically you take off and climb, then the earth rotates around beneath you until your destination arrives, then you decend and land.
Not sure I made that sound too clear but it's just one of those "always wondered" questions I have had and the ATPL notes don't really cover it.
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If we make the numbers easy. 1 deg is 60nm so 360 degs is 21600 (at the equator) Over 24 hours that is 900 kts.
So 21600 is the circumference. Divided by Pi and then by 2 gives a radius of 3437 nm. Flying at 7 miles say, so our radius is now 3444 and therefore our circumference is now 21643 and over 24 hours that comes to 902 kts. So therefore the higher you go the faster you would need to go to keep up with the sun. (Makes sense really, I suppose thats why 'geo-stationary' satellites are doing about 15,000 kts to keep up, cos they are so high)
Think I have that right!
Leezy, not sure about your question, I think though you are asking the same question, ie what speed would you have to go to keep 'geo-stationary' whilst the earth revolves under you. In which case I think it is the answer above (depending on your Lat obviously).
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Sun "rise" in the west? Only as an illusion caused by a vector of the high aircraft velocity towards the setting sun, surely? Simplest example to bring to mind is an aircraft rushing high along a great circle above the equator from night towards a setting sun...and winning the race. The aircraft would be rushing broadly west for maximum effect, depending on the season, n'est-ce pas?
So just a bog standard apparent reversal of the progress of a sunset? - but hold on, what's the need to rush? Surely any aircraft even at the equator can win against a sunset if it is heading directly towards a setting sun in the west? It need only achieve a groundspeed greater than 60 knots and won't the sun then be seen to "rise" above the horizon on the nose? Edit 1: I knew that sounded daft, why didn't I check it! From schoolbook geography it is obviously 1000 statute miles an hour at the equator isn't it? i.e. 60kts x 14.7 isn't it (being pedantic) =882kts or 900 if you like .... Doh!
At other latitudes heading towards the sun, wouldn't the necessary speed be lower per FlyVMO's cosine rule?
Methinks said SR-71 pilot must surely have set himself a more difficult challenge - maybe flying North after sunset and still managing to get the sun to rise again using that cosine effect again - perhaps it even rose straight up and didn't budge from west
(I'm guessing ... horribly...again!)
Quoting from http://www.sr-71.org/blackbird/sr-71... "On September 13, 1974, an SR-71A set a speed record from London to Los Angeles at an average speed of 1,435.587 mph. On July 28, 1976, an SR-71A set an Altitude in Horizontal Flight record at 85,068.997 feet. On that same day, the aircraft set the Speed Over a Closed Course record of 2,193.167 mph. On July 27, 1976, the SR-71 set a Speed Over a Closed Circuit record at a speed of 2,092.294 mph. On September 1, 1974, the airplane set a record from New York to London in 1 hour, 54 minutes, and 56.4 seconds."
I found another quote attributed to an SR-71 pilot — USAF Lt. Col. Gil Bertelson, SR-71 pilot, in 'SR-71 Blackbird: Stories, Tales and Legends,' 2002, who apparently said:
"You know the part in 'High Flight where it talks about putting out your hand to touch the face of God? Well, when we're at speed and altitude in the SR, we have to slow down and descend in order to do that."
Edit 2: I can't help thinking that the speed record in horizontal flight is key to the original question. No other aircraft was got close to being as capable of sustained horizontal flight at anything like that speed, except Concorde??
So just a bog standard apparent reversal of the progress of a sunset? - but hold on, what's the need to rush? Surely any aircraft even at the equator can win against a sunset if it is heading directly towards a setting sun in the west? It need only achieve a groundspeed greater than 60 knots and won't the sun then be seen to "rise" above the horizon on the nose? Edit 1: I knew that sounded daft, why didn't I check it! From schoolbook geography it is obviously 1000 statute miles an hour at the equator isn't it? i.e. 60kts x 14.7 isn't it (being pedantic) =882kts or 900 if you like .... Doh!
At other latitudes heading towards the sun, wouldn't the necessary speed be lower per FlyVMO's cosine rule?
Methinks said SR-71 pilot must surely have set himself a more difficult challenge - maybe flying North after sunset and still managing to get the sun to rise again using that cosine effect again - perhaps it even rose straight up and didn't budge from west
(I'm guessing ... horribly...again!)
Quoting from http://www.sr-71.org/blackbird/sr-71... "On September 13, 1974, an SR-71A set a speed record from London to Los Angeles at an average speed of 1,435.587 mph. On July 28, 1976, an SR-71A set an Altitude in Horizontal Flight record at 85,068.997 feet. On that same day, the aircraft set the Speed Over a Closed Course record of 2,193.167 mph. On July 27, 1976, the SR-71 set a Speed Over a Closed Circuit record at a speed of 2,092.294 mph. On September 1, 1974, the airplane set a record from New York to London in 1 hour, 54 minutes, and 56.4 seconds."
I found another quote attributed to an SR-71 pilot — USAF Lt. Col. Gil Bertelson, SR-71 pilot, in 'SR-71 Blackbird: Stories, Tales and Legends,' 2002, who apparently said:
"You know the part in 'High Flight where it talks about putting out your hand to touch the face of God? Well, when we're at speed and altitude in the SR, we have to slow down and descend in order to do that."
Edit 2: I can't help thinking that the speed record in horizontal flight is key to the original question. No other aircraft was got close to being as capable of sustained horizontal flight at anything like that speed, except Concorde??
Last edited by late developer; 31st Dec 2006 at 00:48.
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The Western sunrise is not only restricted to SR-71 and Concorde 
flights, we mere subsonic mortals can see it too. On a recent U.S.A. to East Asia flying the great circle, we watched the sun set very very slowly in the West, at a time when the Great Circle Track was towards the North-West, and thus, rate of change of Longitude was less than the Earth's rotation. As the Track became more Westerly, at Max Lat of 64°44' North, the sun rose again in the West and steadily became higher, until our rate of change of Longitude again became slower as the Great Circle Track became South-Westerly. I'd figured that at our Max Lat, the Sun was moving West at 384 Knots, against our Ground Speed of 521 Knots.
I've seen the sun set in the East in a humble F27, and on a Northerly Track. As we climbed, our Altitude increase caused a 'premature' sunrise, and, as we descended again soon after on the short sector, it sank below the horizon again in the East.
The 'oddest' sunrise that I've seen was a mid summer flight from Seoul to Vancouver, Great Circle again, the evening / morning twilight slowly moved from Left to Right , until finally it rose in a direction of True North, at LMT midnight, directly over the North Pole, as we moved North-wards on the initial part of the Great Circle Track. It continued to rise and move from Left to Right, and was then in our eyes for most of the Easterly portion of the flight.
Sunrise in the West, Sunset in the East, Sunrise over the North Pole, Sunrise at mid-night? - who said that pilot's weren't gods?
Someone spoke of being geo-stationary. Ummm, did you mean solar stationary? To achieve a geo-stationary state, you'd better join NASA.
Now, can somebody explain why I only had 5Hr:17Min of Christmas this year?
Regards, and Happy New Year,
Old Smokey
flights, we mere subsonic mortals can see it too. On a recent U.S.A. to East Asia flying the great circle, we watched the sun set very very slowly in the West, at a time when the Great Circle Track was towards the North-West, and thus, rate of change of Longitude was less than the Earth's rotation. As the Track became more Westerly, at Max Lat of 64°44' North, the sun rose again in the West and steadily became higher, until our rate of change of Longitude again became slower as the Great Circle Track became South-Westerly. I'd figured that at our Max Lat, the Sun was moving West at 384 Knots, against our Ground Speed of 521 Knots.I've seen the sun set in the East in a humble F27, and on a Northerly Track. As we climbed, our Altitude increase caused a 'premature' sunrise, and, as we descended again soon after on the short sector, it sank below the horizon again in the East.
The 'oddest' sunrise that I've seen was a mid summer flight from Seoul to Vancouver, Great Circle again, the evening / morning twilight slowly moved from Left to Right , until finally it rose in a direction of True North, at LMT midnight, directly over the North Pole, as we moved North-wards on the initial part of the Great Circle Track. It continued to rise and move from Left to Right, and was then in our eyes for most of the Easterly portion of the flight.
Sunrise in the West, Sunset in the East, Sunrise over the North Pole, Sunrise at mid-night? - who said that pilot's weren't gods?
Someone spoke of being geo-stationary. Ummm, did you mean solar stationary? To achieve a geo-stationary state, you'd better join NASA.
Now, can somebody explain why I only had 5Hr:17Min of Christmas this year?
Regards, and Happy New Year,
Old Smokey
Last edited by Old Smokey; 31st Dec 2006 at 02:44. Reason: Forgot a good bit
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A question I have always wondered :-
If you are heading west, what speed would you have to be travelling at to have the earth rotate beneath you whilst you remained stationary relative to the moving earth. Basically you take off and climb, then the earth rotates around beneath you until your destination arrives, then you decend and land.
Not sure I made that sound too clear but it's just one of those "always wondered" questions I have had and the ATPL notes don't really cover it.
If you are heading west, what speed would you have to be travelling at to have the earth rotate beneath you whilst you remained stationary relative to the moving earth. Basically you take off and climb, then the earth rotates around beneath you until your destination arrives, then you decend and land.
Not sure I made that sound too clear but it's just one of those "always wondered" questions I have had and the ATPL notes don't really cover it.
We do not live ON the earth, we live and move IN it, that is at the bottom of an ocean of gas, just like lobsters live at the bottom of an ocean of liquid. So, when we fly, we move inside that ocean, like submarine in dive, only in gas i.o liquid. However, I do understand the meaning of your question. It would equate to fly west at the equator and keep the sun stationary. Haven't got the formula in memory, but start with 15 deg/hrs times a trigonometric arc function of the earth radius plus the altitude.
Happy New Year.
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Physically speaking, you would have to climb on orbit.
We do not live ON the earth, we live and move IN it, that is at the bottom of an ocean of gas, just like lobsters live at the bottom of an ocean of liquid. So, when we fly, we move inside that ocean, like submarine in dive, only in gas i.o liquid. However, I do understand the meaning of your question. It would equate to fly west at the equator and keep the sun stationary. Haven't got the formula in memory, but start with 15 deg/hrs times a trigonometric arc function of the earth radius plus the altitude.
Happy New Year.
We do not live ON the earth, we live and move IN it, that is at the bottom of an ocean of gas, just like lobsters live at the bottom of an ocean of liquid. So, when we fly, we move inside that ocean, like submarine in dive, only in gas i.o liquid. However, I do understand the meaning of your question. It would equate to fly west at the equator and keep the sun stationary. Haven't got the formula in memory, but start with 15 deg/hrs times a trigonometric arc function of the earth radius plus the altitude.
Happy New Year.
space and time change when you travel.
People living at the equator stay younger than people living close of the poles.
so even if we we are bonded to a place , we are all some separated entities living in our own time and in our own space.
ask Einstein for more!I have to go out to buy some pop!
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Happy New Year, especially to the swathe of Pacific Islanders, Antipodeans, East Asians, and persons dancing across lines of longitude at the poles who've already been there today, so to speak
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Leezyjet, hi there. As far as remember at the equator it's 900 NM/H as per quotation above 15 DEG per hour. It does change though with latitude with COS of the angle or latitude. Lets say at 60 deg latitude the speed would be 900*cos60deg=450 As one can see it's half of the speed from the equator.
Here is the million dollar question what's the speed on the north pole? By the way isn't it the earth's rotation speed?
Happy new year to everyone!!!
Here is the million dollar question what's the speed on the north pole? By the way isn't it the earth's rotation speed?
Happy new year to everyone!!!
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Time here for a cup of tea and an early piece of cake while I try to find a way in
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not "totally" true, jump from a chair, and you will "notice", u don't land straight down but a few pico (1000th of 1000th of mm)meter offset.same theory when you travel, time contracts of a few microseconds making your self a time traveler without noticing it(travels make you younger).
space and time change when you travel.
People living at the equator stay younger than people living close of the poles.
so even if we we are bonded to a place , we are all some separated entities living in our own time and in our own space.
ask Einstein for more!I have to go out to buy some pop!
space and time change when you travel.
People living at the equator stay younger than people living close of the poles.
so even if we we are bonded to a place , we are all some separated entities living in our own time and in our own space.
ask Einstein for more!I have to go out to buy some pop!
Thank you Mr de Batz-Castelmore! I did not realize Einstein had established the Lorentz contraction and hence the Lorentz transformations. Maybe Einstein (1879-1955) suggested it to Lorentz (1853 - 1928) when he was a child?
Thread Starter
Thanks everyone, keep them coming....
Old Smokey--how did you calculate the speed of the apparent motion of the sun on your westward sector? My Chistmas was similar, about 4 hours of daylight. Saw sunrise during take-off roll, seemed almost instantly to be late afternoon and sunset west of Iceland.
GF
Old Smokey--how did you calculate the speed of the apparent motion of the sun on your westward sector? My Chistmas was similar, about 4 hours of daylight. Saw sunrise during take-off roll, seemed almost instantly to be late afternoon and sunset west of Iceland.
GF
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Hi galaxy flyer,
A nice good fun thread, thanks for starting it.
I figured the sun's ground speed as 900 Kt (Equatorial speed) X Cosine Latitude, i.e.
900 X Cos 64°44' = 384 Kt.
Sorry that you also had a short Christmas Day, it seems that you were flying East, we were going West, passed 00:00 Local time on 25th December a few hours after Takeoff. As a Westerly flight it should have lengthened Christmas day, but 5Hr:17min later crossed the International Date Line into 26th December, and we hadn't even finished hanging the mistletoe above the cockpit door
At least I'm having a 25 hour New Year's Day today, thanks to a Westerly Non-International Date Line flight.
Time travellers, that's what we are.
Regards,
Old Smokey
A nice good fun thread, thanks for starting it.
I figured the sun's ground speed as 900 Kt (Equatorial speed) X Cosine Latitude, i.e.
900 X Cos 64°44' = 384 Kt.
Sorry that you also had a short Christmas Day, it seems that you were flying East, we were going West, passed 00:00 Local time on 25th December a few hours after Takeoff. As a Westerly flight it should have lengthened Christmas day, but 5Hr:17min later crossed the International Date Line into 26th December, and we hadn't even finished hanging the mistletoe above the cockpit door
At least I'm having a 25 hour New Year's Day today, thanks to a Westerly Non-International Date Line flight.
Time travellers, that's what we are.
Regards,
Old Smokey
