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Walter Banks
Guest
Tue Mar 09, 2010 10:13 pm
rickman wrote:
Quote:
I can't say this for certain, but I believe the combination of length
of day and elevation of the sun at the zenith is a unique combination
for each day of the year and latitude. So I think you can get your
latitude the same day.
It is close but not exact. The earth's orbit is not an exact number of
days. For the calendar's purpose we accumulate errors and adjust
the calendar. These adjustments are every 4 years and sometimes
on the century. There are other errors that have an impact on the
observations depending on the required accuracy.
I saw a sundial on a beach near Kobe Japan that had elaborate
error correcting instructions that was probably good to a second
after ten minutes of calculations. There were a lot of factors involved
it accounted for earths orbital period
Quote:
But I'm not sure you don't have the same two
day ambiguity. Otherwise I think the combination is unique. Even the
North-South issue can be resolved because of the eccentricity of the
Earth's orbit making things a little different in the two
hemispheres. But you may also be foiled beyond the artic/anartic
circles where the sun never sets. Then you only get one parameter,
the elevation at the zenith. But you might be able to make up for
that by measuring the time between the sun at due east and due west...
other than at the poles where there is no east or west... ;^)
Above the arctic circle the sun 24 hour path is tilted but there are other
factors that are significant. For a couple weeks around June 21 the
sun never sets as far as 80 miles or so south of the arctic circle.
Most of this is due to the optic effects of the atmosphere. Even above
the arctic circle actual and observed position of the sun has significant
differences.
Regards,
w..
--
Walter Banks
Byte Craft Limited
http://www.bytecraft.com
rickman
Guest
Tue Mar 09, 2010 10:30 pm
On Mar 9, 12:20 pm, D Yuniskis <not.going.to...@seen.com> wrote:
Quote:
Jasen Betts wrote:
So (thinking in terms of a *truly* unique hack), if you *watched*
the motion over the course of a particular day (e.g., 'yesterday'),
could you *uniquely* determine that day?
Given lattitude and longitude (or equivalent) and sufficiently good
instruments, and the right data and skills, yes.
So, a *device* that watched these things could deduce date/time (?)
How much more would it have to do to deduce location (or, at least,
latitude)? Probably just watch for a longer period of time?
I can't say this for certain, but I believe the combination of length
of day and elevation of the sun at the zenith is a unique combination
for each day of the year and latitude. So I think you can get your
latitude the same day. But I'm not sure you don't have the same two
day ambiguity. Otherwise I think the combination is unique. Even the
North-South issue can be resolved because of the eccentricity of the
Earth's orbit making things a little different in the two
hemispheres. But you may also be foiled beyond the artic/anartic
circles where the sun never sets. Then you only get one parameter,
the elevation at the zenith. But you might be able to make up for
that by measuring the time between the sun at due east and due west...
other than at the poles where there is no east or west... ;^)
Rick
D Yuniskis
Guest
Tue Mar 09, 2010 10:38 pm
Hi Walter,
Walter Banks wrote:
Quote:
I saw a sundial on a beach near Kobe Japan that had elaborate
error correcting instructions that was probably good to a second
after ten minutes of calculations. There were a lot of factors involved
it accounted for earths orbital period
I always thought a cool hack would be a motorized sundial.
(i.e., the motorization being a cleverly hidden aspect)
E.g., with nice, evenly spaced markings -- and a motor to
rotate the whole assembly such that the shadow fell
"where it should" (on this nicely marked indicator).
It;s the sort of thing that would elicit comment *only*
from someone who *knew* it was "quite impossible" to
work as it *suggests* it works...
(obviously, I like things that mess with people's heads :> )
-jg
Guest
Tue Mar 09, 2010 11:17 pm
On Mar 10, 6:20 am, D Yuniskis <not.going.to...@seen.com> wrote:
Quote:
Jasen Betts wrote:
Given lattitude and longitude (or equivalent) and sufficiently good
instruments, and the right data and skills, yes.
So, a *device* that watched these things could deduce date/time (?)
How much more would it have to do to deduce location (or, at least,
latitude)? Probably just watch for a longer period of time?
The fish-hook here is in the careful wording of
"and sufficiently good instruments, and the right data and skills,
yes"
So a smarter question, could be what is practical ?
- and using what measurement systems ?
I found this revealing page, which has real datapoints,
and a practical location (ie less than ideal)
http://www.austintek.com/astro/analemma/analemma.html
Most revealing are the nice dots-on-the-door
http://www.austintek.com/astro/analemma/images/4215.door_from_inside_rotate..jpg
and the red arcs, are snapshots of the actual path,
~4wks - note they include a dot on alternating sides
of the analemma, as the 12 arcs interlace.
This site below shows the analemma actually moves yr-yr, so that's
more data to track ;)
http://myweb.tiscali.co.uk/moonkmft/Articles/EquationOfTime.html
-jg
Paul Keinanen
Guest
Wed Mar 10, 2010 5:00 am
On Tue, 09 Mar 2010 10:20:08 -0700, D Yuniskis
<not.going.to.be_at_seen.com> wrote:
Quote:
Jasen Betts wrote:
So (thinking in terms of a *truly* unique hack), if you *watched*
the motion over the course of a particular day (e.g., 'yesterday'),
could you *uniquely* determine that day?
Given lattitude and longitude (or equivalent) and sufficiently good
instruments, and the right data and skills, yes.
So, a *device* that watched these things could deduce date/time (?)
How much more would it have to do to deduce location (or, at least,
latitude)? Probably just watch for a longer period of time?
By observing when the sum passes the meridian, one cloud free week in
the spring and one in the autumn should give a quite good resolution
for the latitude, provided that some internal time reference is
capable of measuring the number of days between the measuring periods
with at least +/-12 hour accuracy. During one week long period the sun
moves south and on he other it moves north.
Of course, there is the north/south hemisphere ambiguity, but with
additional sensors to the left and right of the meridian line should
help solve this ambiguity. After all, in order to detect meridian
passing you would have to align the device towards true north.
A camera with at least 150 degree field of view pointing directly
upwards towards zenith, should be able to detect the orientation,
latitude, date and local solar time within a year of observations.
Joe Pfeiffer
Guest
Wed Mar 10, 2010 6:29 am
Paul Keinanen <keinanen_at_sci.fi> writes:
Quote:
On Tue, 09 Mar 2010 10:20:08 -0700, D Yuniskis
not.going.to.be_at_seen.com> wrote:
Jasen Betts wrote:
So (thinking in terms of a *truly* unique hack), if you *watched*
the motion over the course of a particular day (e.g., 'yesterday'),
could you *uniquely* determine that day?
Given lattitude and longitude (or equivalent) and sufficiently good
instruments, and the right data and skills, yes.
So, a *device* that watched these things could deduce date/time (?)
How much more would it have to do to deduce location (or, at least,
latitude)? Probably just watch for a longer period of time?
By observing when the sum passes the meridian, one cloud free week in
the spring and one in the autumn should give a quite good resolution
for the latitude, provided that some internal time reference is
capable of measuring the number of days between the measuring periods
with at least +/-12 hour accuracy. During one week long period the sun
moves south and on he other it moves north.
Of course, there is the north/south hemisphere ambiguity, but with
additional sensors to the left and right of the meridian line should
help solve this ambiguity. After all, in order to detect meridian
passing you would have to align the device towards true north.
A camera with at least 150 degree field of view pointing directly
upwards towards zenith, should be able to detect the orientation,
latitude, date and local solar time within a year of observations.
The hardware for this is in the current issue of Circuit Cellar.
Different programming needed....
--
As we enjoy great advantages from the inventions of others, we should
be glad of an opportunity to serve others by any invention of ours;
and this we should do freely and generously. (Benjamin Franklin)
Jasen Betts
Guest
Wed Mar 10, 2010 11:57 am
On 2010-03-09, D Yuniskis <not.going.to.be_at_seen.com> wrote:
Quote:
Jasen Betts wrote:
So (thinking in terms of a *truly* unique hack), if you *watched*
the motion over the course of a particular day (e.g., 'yesterday'),
could you *uniquely* determine that day?
Given lattitude and longitude (or equivalent) and sufficiently good
instruments, and the right data and skills, yes.
So, a *device* that watched these things could deduce date/time (?)
How much more would it have to do to deduce location (or, at least,
latitude)? Probably just watch for a longer period of time?
6 months would be sufficient,
probably shorter periods too.
the earths's axial wobble, and orbital precession, are probably going
to make it impossible do it in less than a week.
OTOH if you can see the stars and planets at night that would help a
lot...
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