Post by mikedunlavey on Jul 8, 2017 23:11:53 GMT
I think there's a problem with your sundial construction.
1) You're mounting the gnomon perpendicular to the ground, and 2) you're only considering the shadow of the tip of the gnomon, not the gnomon as a line.
This sort-of works on a gleason map. It works in the sense that the shadow of the tip of the gnomon does indeed trace out a copy of the sun's circular path, 15 degrees per hour.
The caveat is that the shadow cast by the line of the gnomon does not move 15 degrees per hour, except at mid-day, and the base of the gnomon is not in the center, and some places even outside the circle.
And of course, it does not work on a globe, as you demonstrated. It is a sundial for flat-earth.
A sundial for a globe earth consists of a circle in 24 segments, with the gnomon mounted perpendicular to the circle, in the center of the circle.
But the gnomon is not mounted perpendicular to the ground. You point it due north at the horizon, end then elevate it by your latitude.
In the southern hemisphere, this means pointing it below the northern horizon.
When used on a globe, the shadow of the entire gnomon line points to each of the 24 segments, one per hour (except for nighttime, of course).
This is how real-world sundials are made.
Conclusion - you've invented a sundial that works on flat-earth but not a globe, and sundials used in the real world are the type that work on a globe and not on flat earth.
1) You're mounting the gnomon perpendicular to the ground, and 2) you're only considering the shadow of the tip of the gnomon, not the gnomon as a line.
This sort-of works on a gleason map. It works in the sense that the shadow of the tip of the gnomon does indeed trace out a copy of the sun's circular path, 15 degrees per hour.
The caveat is that the shadow cast by the line of the gnomon does not move 15 degrees per hour, except at mid-day, and the base of the gnomon is not in the center, and some places even outside the circle.
And of course, it does not work on a globe, as you demonstrated. It is a sundial for flat-earth.
A sundial for a globe earth consists of a circle in 24 segments, with the gnomon mounted perpendicular to the circle, in the center of the circle.
But the gnomon is not mounted perpendicular to the ground. You point it due north at the horizon, end then elevate it by your latitude.
In the southern hemisphere, this means pointing it below the northern horizon.
When used on a globe, the shadow of the entire gnomon line points to each of the 24 segments, one per hour (except for nighttime, of course).
This is how real-world sundials are made.
Conclusion - you've invented a sundial that works on flat-earth but not a globe, and sundials used in the real world are the type that work on a globe and not on flat earth.