How hard is to build a processor?

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

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

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)

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 ;)

-jg

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 :> )

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....

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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