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A question about GMT
- Frank Ryan
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- Super Giant
Limerick is behind London in terms of
rotation?
Eg.
if you hit a stopwatch over grenwitch
at 12:00 how long would it take for Limerick
(or its line of longitude) to pass under you.
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- Paul Evans
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Paul.
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- Frank Ryan
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My Astrophotography
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- dave_lillis
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world time -> 24hours=86400seconds
world latitude -> 360degrees=1296000seconds of arc
1296000/86400=15, so 1 second of time = 15 arcseconds of latitude.
so Limerick is 8degrees 37mwest=31020 seconds of arc
giving us, 31020/15=2068seconds=34mins 28 seconds
I didnt use an exact latitude, the more accurate you have it, the more accurate a result you get
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Carrying around my 20" obsession is going to kill me,
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- stepryan
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Dave_Lillis wrote: well think of it as a simple ratio,
world time -> 24hours=86400seconds
world latitude -> 360degrees=1296000seconds of arc
1296000/86400=15, so 1 second of time = 15 arcseconds of latitude.
so Limerick is 8degrees 37mwest=31020 seconds of arc
giving us, 31020/15=2068seconds=34mins 28 seconds
I didnt use an exact latitude, the more accurate you have it, the more accurate a result you get
also the result will vary depending where you are on the earths surface you are located. the earth is an oblate spheriod not a perfect sphere. this will also affect the result as the lines of latitude / longitude are not perfectly equal.
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- mjc
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Only the angular seperation between local meridian and any other reference meridian is needed to calculate local time.
Think about it - angular seperation from centre of Earth is equally spaced between lines of longitude - as is the corresponding distance on the ground (at any given constant latitude). Of course this distance is shorter as latitude approaches the pole - but this doesn't affect time measurement as a ring of latitude still rotates once per day.. However, the spacing on the ground *between* lines of latitude must differ slightly (at any given constant longidtude) as curvature is changing in the north-south direction. It doesn't affect the calculation of local time.
That is as per my limited understanding.
Mark C.
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