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> On May 5, 8:01 am, nos...@de-ster.demon.nl (J. J. Lodder) wrote:
> > > That causes the distance of a degree of
> > > latitude to be dependent upon the latitude in contrast to the
> > > generally accepted value of a nautical mile per degree for a spherical
> > > earth.
> > > latitude to be dependent upon the latitude in contrast to the
> > > generally accepted value of a nautical mile per degree for a spherical
> > > earth.
> > A nautical mile is 1852 meter (exactly)
> > and nothing else,
> > Jan
> > and nothing else,
> > Jan
>
> I have no problem with that definition and don't find it inconsistent
> with the historical one nautical mile per minute (thanks Roy)
> spherical earth definition. This is from Ed Williams Aviation Page
> (very famous):
>
> 'Note: the nautical mile is currently defined to be 1852 meters -
> which to be consistent with its historical definition implies the
> earth's radius to be 1.852 * (180*60/pi) = 6366.71 km, which indeed
> lies between the currently accepted ( WGS84) equatorial and polar
> radii of 6378.137 and 6356.752 km, respectively. Other choices of the
> earth's radius in this range are consistent with the spherical
> approximation and may for some specialized purposes be preferred'.
>
> I suspect the earth radius would indeed settle into cited range if we
> stopped it from turning and allowed it time to lose its 'mid-rib
> bulge'.
> I have no problem with that definition and don't find it inconsistent
> with the historical one nautical mile per minute (thanks Roy)
> spherical earth definition. This is from Ed Williams Aviation Page
> (very famous):
>
> 'Note: the nautical mile is currently defined to be 1852 meters -
> which to be consistent with its historical definition implies the
> earth's radius to be 1.852 * (180*60/pi) = 6366.71 km, which indeed
> lies between the currently accepted ( WGS84) equatorial and polar
> radii of 6378.137 and 6356.752 km, respectively. Other choices of the
> earth's radius in this range are consistent with the spherical
> approximation and may for some specialized purposes be preferred'.
>
> I suspect the earth radius would indeed settle into cited range if we
> stopped it from turning and allowed it time to lose its 'mid-rib
> bulge'.
Sure, but it is unlikely that the minute of latutude
would settle on 1852 m exactly.
It would be close though for 1852 was selected
as the integer closest to the averaage minute
along a polar quadrant.
Jan
+ nospam@de-ster.demon.nl (J. J. Lodder):
>> 'Note: the nautical mile is currently defined to be 1852 meters -
>> which to be consistent with its historical definition implies the
>> earth's radius to be 1.852 * (180*60/pi) = 6366.71 km, which indeed
>> lies between the currently accepted ( WGS84) equatorial and polar
>> radii of 6378.137 and 6356.752 km, respectively. Other choices of the
>> earth's radius in this range are consistent with the spherical
>> approximation and may for some specialized purposes be preferred'.
>>
>> I suspect the earth radius would indeed settle into cited range if we
>> stopped it from turning and allowed it time to lose its 'mid-rib
>> bulge'.
>> which to be consistent with its historical definition implies the
>> earth's radius to be 1.852 * (180*60/pi) = 6366.71 km, which indeed
>> lies between the currently accepted ( WGS84) equatorial and polar
>> radii of 6378.137 and 6356.752 km, respectively. Other choices of the
>> earth's radius in this range are consistent with the spherical
>> approximation and may for some specialized purposes be preferred'.
>>
>> I suspect the earth radius would indeed settle into cited range if we
>> stopped it from turning and allowed it time to lose its 'mid-rib
>> bulge'.
Actually, if we ignore any changes in volume due to compressibility
effects then the earth rendered stationary would become a sphere of
radius 6371.001 km, resulting in a nautical mile equal to 1853.249 m.
--
* Harald Hanche-Olsen <URL:http://www.math.ntnu.no/~hanche/>
- It is undesirable to believe a proposition
when there is no ground whatsoever for supposing it is true.
-- Bertrand Russell
Hi,
Obviously the tectonic plates move, so every nanometer of land moves over time.
Latitude is the distance from the equator. Regardless of where it is.
As Greenwich moves, so does the prime meridian and longitude.
This does bring up an interesting problem.
If a catastrophic event happen to the earth. The rotational poles & magnetic
poles moved, how would we define North?
Take Uranus for example.
It's rotational north is tilted at 97.77 degrees (points at the sun). It's
magnetic north pole is another 59 degrees counter
clockwise from the rotational pole (points down).
All other planets have their poles orientated as the Earth's. (north is up in
relation to the orbit around the sun (ecliptic))
What if this happens to the Earth?
Would we call it an ice age? Is that what an ice age is? The Earth flipping its
poles? Why do sedimentary deposits have opposite
magnetic polarity at 250000 year intervals?
How would GPS work?
Where would the datums be? (lat/long)
Since we most likely would all be dead it probably doesn't matter...
Anyone know if there is a correction built into the GPS system for such an
event? ;<)
John
>I heard an arctic paleontologist taking on the radio today. He mentioned
something about the latitude of some of his fossil finds
>not being the same number today as it would have been when the animal was
alive. The implication that I took from his statement
>is that the latitude of earth's geographic features can change over geological
time periods. I'm not taking about continental
>drift or anything like that. The man seemed to be saying that a 'stationary'
point on the earth's surface would be described by
>varying latitude numbers over very long periods of time.
> I didn't really understand this so I've been trying to do some research about
it on the web. The best I can come up with is this:
> I didn't really understand this so I've been trying to do some research about
> 1) latitude is referenced to the equator, 2) the equator is defined by the
great circle that is equidistant from the geographic
> poles, and 3) the precession of the earth's rotation changes the location of
the earth's rotation axis in space. I suppose if this
> precession changed the physical location of the earth's poles with respect to
the earth's geographical features, then the latitude
> of earth's geographic features would also change over long time periods as the
equator changed position. But I didn't think that
> the location of the axis changed because of precession; only its tilt.
> Is there I any validity in what I think this man said? Perhaps I
misunderstood what he meant. Just curious. Thanks.
> Is there I any validity in what I think this man said? Perhaps I
>
>Hi,
>Obviously the tectonic plates move, so every nanometer of land moves over time.
>Latitude is the distance from the equator. Regardless of where it is.
>As Greenwich moves, so does the prime meridian and longitude.
>This does bring up an interesting problem.
>If a catastrophic event happen to the earth. The rotational poles & magnetic
poles moved, how would we define North?
>Obviously the tectonic plates move, so every nanometer of land moves over time.
>Latitude is the distance from the equator. Regardless of where it is.
>As Greenwich moves, so does the prime meridian and longitude.
>This does bring up an interesting problem.
>If a catastrophic event happen to the earth. The rotational poles & magnetic
>Take Uranus for example.
>It's rotational north is tilted at 97.77 degrees (points at the sun). It's
magnetic north pole is another 59 degrees counter
>It's rotational north is tilted at 97.77 degrees (points at the sun). It's
>clockwise from the rotational pole (points down).
>All other planets have their poles orientated as the Earth's. (north is up in
relation to the orbit around the sun (ecliptic))
>All other planets have their poles orientated as the Earth's. (north is up in
>What if this happens to the Earth?
>Would we call it an ice age? Is that what an ice age is? The Earth flipping its
poles? Why do sedimentary deposits have opposite
>Would we call it an ice age? Is that what an ice age is? The Earth flipping its
>magnetic polarity at 250000 year intervals?
>How would GPS work?
>Where would the datums be? (lat/long)
>Since we most likely would all be dead it probably doesn't matter...
>Anyone know if there is a correction built into the GPS system for such an
event? ;<)
>How would GPS work?
>Where would the datums be? (lat/long)
>Since we most likely would all be dead it probably doesn't matter...
>Anyone know if there is a correction built into the GPS system for such an
>John
All Maps would have to be periodically re-drawn to accommodate the new
positions of landscape relative to the axis of the earth's rotation.
I suspect with hi-power computers and laser-surveying, this isn't a
really impossible challenge anymore.
But there is a difference between precision and accuracy. GPS may
continue to be precise, but it's accuracy is going to be impaired by
flaws in existing maps. It may continue to give precise coordinates,
but when you "plug those coordinates into your mapping software," you
may not be where you think you are, relative to the
terrain/landscape/geography.
Change isn't needed on the GPS side of the equation, it is needed on
the mapping side. But I suspect, since we are not moving around on
these tectonic plates all that quickly, we should still be good to go
for a human lifetime without ending up in Iowa when we wanted to go to
Minnesota instead...barring any cataclysmic event like an asteroid
impact.
Lg
> Hi,
> Obviously the tectonic plates move, so every nanometer of land moves over
> time. Latitude is the distance from the equator. Regardless of where it
> is. As Greenwich moves, so does the prime meridian and longitude.
> Obviously the tectonic plates move, so every nanometer of land moves over
> time. Latitude is the distance from the equator. Regardless of where it
> is. As Greenwich moves, so does the prime meridian and longitude.
No, the prime meridian is no longer locked to Greenwich.
The brass meridian line in the observatory is about 100 meters off.
> This does bring up an interesting problem.
>
> If a catastrophic event happen to the earth. The rotational poles &
> magnetic poles moved, how would we define North?
>
> If a catastrophic event happen to the earth. The rotational poles &
> magnetic poles moved, how would we define North?
Anyway you want.
However (unless the field goes multipolar)
the magnetic pole will always be the point where the field is vertical.
The geographic pole is always where the angular momentum vector
intersects the surface of the earth.
> Take Uranus for example.
> It's rotational north is tilted at 97.77 degrees (points at the sun).
> It's rotational north is tilted at 97.77 degrees (points at the sun).
Better: nearly lies in the ecliptic plane.
It will point near the sun only once an orbit.
> It's magnetic north pole is another 59 degrees counter
> clockwise from the rotational pole (points down).
> All other planets have their poles orientated as the Earth's.
> (north is up in relation to the orbit around the sun (ecliptic))
>
> What if this happens to the Earth?
> Would we call it an ice age? Is that what an ice age is?
> clockwise from the rotational pole (points down).
> All other planets have their poles orientated as the Earth's.
> (north is up in relation to the orbit around the sun (ecliptic))
>
> What if this happens to the Earth?
> Would we call it an ice age? Is that what an ice age is?
Certainly not.
> The Earth flipping its poles? Why do sedimentary deposits have opposite
> magnetic polarity at 250000 year intervals?
> magnetic polarity at 250000 year intervals?
Because the magnetic polarity changes once in a while.
(not periodically though, and certainly not 'at intervals')
> How would GPS work?
Of course it would work.
GPS has nothing to do with coordinates, or with any pole.
It tells you where you are in space.
(that is, wrt the constellation)
You can represent that in any coordinate system you like.
Best,
Jan
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