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No, that's not quite correct. If you're at the North Pole, for example, the only direction is south. If the Sun is up, it will still be moving from east to west, thus the shadow on the sundial will move west to east ... CW in that frame of reference.
It doesn't make any difference whether the sundial is horizontal or vertical. Both variations rely on the east-to-west motion of the Sun to record time.
You are correct that, in the southern hemisphere, sundials need to face north (south of 23.5 ° latitude) to consistently cast a shadow to the south. But that shadow will then move CCW in the southern hemisphere frame of reference.
You are right about the exact point at the North Pole. At that point your shadow rotates round at your feet, CW as you look down on the earth.
At near the North Pole, you still have the same phenomenon, except there is still a north-south distinction, so the shadow rotates, like I said before, West-North-East-South-West.
Which way a sun dial should face? The horizontal style has no issue obviously. The vertical kind needs to face where the sun is, or else it just has a black face. In the northern parts, you want it to face south (though not necessarily exactly south). The tip of the rod that tells time, will cast its shadow first in West, moving lower to the bottom toward noon, then ending in East. And when you look at it while facing north (it facing south), that's a CCW rotation.
I don't think I can do much better than that.
Heimhenge said
No, that's not quite correct. If you're at the North Pole, for example, the only direction is south. If the Sun is up, it will still be moving from east to west, thus the shadow on the sundial will move west to east ... CW in that frame of reference.
If the only direction is south, the use of east and west is not just confusing, it's just plain wrong.
Let's poke a barber pole candy cane at Santa's house as a sundial.. At roughly 12:00 Zulu, the sun will appear to come from the Isle of Wight. About five hours later, it will appear to come from Lancaster. Pennsylvania. That is, the sun seems to revolve around the sundial in a clockwise manner and the shadow as well, although out of phase by pi radians.
Poke a skinny penguin in the ice of Antarctica, as another sundial. At about 05:00 Zulu, the sun will appear in the direction of Quito. About five hours later, the sun will be coming from the direction of Sydney. However, as we're on the underside of the Earth, we are looking at the sundial from underneath, which means the sun (and the out-pf-phase shadow) is still moving in a clockwise direction.
You could check it out on a computer, I suppose, but that's a bad idea, as most computers have lost 39 seconds of time since 1970.
deaconB said
Heimhenge said
No, that's not quite correct. If you're at the North Pole, for example, the only direction is south. If the Sun is up, it will still be moving from east to west, thus the shadow on the sundial will move west to east ... CW in that frame of reference.If the only direction is south, the use of east and west is not just confusing, it's just plain wrong.
Let's poke a barber pole candy cane at Santa's house as a sundial.. At roughly 12:00 Zulu, the sun will appear to come from the Isle of Wight. About five hours later, it will appear to come from Lancaster. Pennsylvania. That is, the sun seems to revolve around the sundial in a clockwise manner and the shadow as well, although out of phase by pi radians.
Poke a skinny penguin in the ice of Antarctica, as another sundial. At about 05:00 Zulu, the sun will appear in the direction of Quito. About five hours later, the sun will be coming from the direction of Sydney. However, as we're on the underside of the Earth, we are looking at the sundial from underneath, which means the sun (and the out-pf-phase shadow) is still moving in a clockwise direction.
You could check it out on a computer, I suppose, but that's a bad idea, as most computers have lost 39 seconds of time since 1970.
Heimhenge is correct.
Since Quito is on the equator, let's forget Lancaster. To one standing at the north pole, Quito is to the right of the Isle of Wight. To one standing at the south pole, Quito is to the left of the Isle of Wight. 'Righty tighty' is CW; 'Lefty loosie' is CCW.
BTW, the straight edge of the gnomon matches a line from the Southern Cross to Polaris. So gnomons at the Poles are best made by vertical poles.
Robert said: Which way a sun dial should face? The horizontal style has no issue obviously. The vertical kind needs to face where the sun is, or else it just has a black face. In the northern parts, you want it to face south (though not necessarily exactly south). The tip of the rod that tells time, will cast its shadow first in West, moving lower to the bottom toward noon, then ending in East. And when you look at it while facing north (it facing south), that's a CCW rotation.
I stand corrected regarding sundials attached to vertical south-facing walls (in the northern hemisphere above latitude 23.5 °). The shadow motion would indeed be CCW in that case. I've never see that type of sundial, but know they are in use. I have a classic horizontal sundial in my front yard. It's properly oriented and reasonably accurate. And since AZ doesn't observe daylight saving time, the sundial needs no seasonal corrections. My sundial has a series of hour-mark lines for different seasons and Sun altitudes - not a single hour-mark line like the cheap garden variety sundials you'd find at, say, Home Depot.
The problem with sundials mounted on vertical south-facing surfaces is that, after the Vernal Equinox, the Sun will set north of due west, and that vertical surface will then be in shade, rendering the sundial useless near sunrise and sunset for half the year. I'm sure they have a decorative architectural niche, but if you're serious about using a sundial, you want the classic horizontal type with multiple hour-mark lines.
Glenn, I think this "War of the Words" is over at this point. 
Tromboniator said: If I ever have occasion to construct a fantasy world it will be a requirement that Gnomon is an island.
My initial impression was that your clever non sequitur had ended this thread. Then it hit me: Could Gnomon be a peninsula?
[Younger forum members will have a tough time with that one.]
Heimhenge said
Tromboniator said: If I ever have occasion to construct a fantasy world it will be a requirement that Gnomon is an island.
My initial impression was that your clever non sequitur had ended this thread. Then it hit me: Could Gnomon be a peninsula?
[Younger forum members will have a tough time with that one.]
New Zebedee was on the lower peninsula, but it's us old geezers that are more likely to have trouble with that.
Tromboniator said: "After Bathing at Baxter's"
I figured you might be a Airplane fan.
Not a lot of room for trombones in their music, but I can follow along on a few of their songs with my electric bass. I especially like Saturday Afternoon from that album, but much of their music is pretty complex and hard to play (at least for a beginner like me). Man, this thread has really diverged from the original question. Not like this hasn't happened before, but then, that's one of the reasons I love this forum.
But to respond to your comment, I expect that, to be a peninsula, it would largely depend on who you were bathing with.
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