3 ms·

Doesn’t N or S reverse at noon? Imagine (for simplicity) that we have 6a to 6p with solar noon at 12p. Then if I put my right arm in my shadow at 6am and my o

Doesn’t N or S reverse at noon? Imagine (for simplicity) that we have 6a to 6p with solar noon at 12p. Then if I put my right arm in my shadow at 6am and my other arm 180 degrees from it, then I’ll be facing South. If I do the same thing at 11 am, I form a big wedge with my right arm on the NW side, again facing South. But at noon that changes: the sun is directly South from me, so my right arm is North and my other arm is in the same spot, so I turn around to face North. From there, my right arm is on the NE side, and my left arm makes a widening wedge as I face North — until at 6pm, I’m standing with my right arm facing East and my left arm opposite it, facing North.

HillRat 4y ago
Yes -- the article doesn't explain this, but in the morning you use the clockwise side of the hour hand to find south, and in the afternoon the counter-clockwise side (IIRC).
mckeed 4y ago
It doesn't work at 6:00 unless you know which way to face. At 11am you should have a small wedge, and your left arm should be in the shadow, in order to not point both arms straight behind you. At 1pm your right arm will be in the shadow for the same reason, so you're still facing north.
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- bigiain 4y ago
  At sunrise or sunset, it's pretty obvious which way east or west is. At least to a first approximation. For a second approximation you'll want to interpolate between the equinox and solstice and use that to approximate an allowance for the ~24 degree tilt of earths rotation axis. That second approximation error is there for all times that are not midday, but reduce to zero as you approach midday. A third approximation might be to allow to the offset between your local timezone and solar midday. Where I am (Sydney) we are fairly close to the middle of the +10 and +11 timezone boundaries, so solar noon is within a few minutes of timezones noon. Perth on the other hand is way out to the west of it's timezone, so solar noon there is almost 25 minutes off from timezone noon. So "watch north" in Perth will be about 7.5 degrees off "true north".

HillRat 4y ago

Yes -- the article doesn't explain this, but in the morning you use the clockwise side of the hour hand to find south, and in the afternoon the counter-clockwise side (IIRC).

mckeed 4y ago

It doesn't work at 6:00 unless you know which way to face. At 11am you should have a small wedge, and your left arm should be in the shadow, in order to not point both arms straight behind you. At 1pm your right arm will be in the shadow for the same reason, so you're still facing north.

deleted 4y ago
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bigiain 4y ago
At sunrise or sunset, it's pretty obvious which way east or west is. At least to a first approximation. For a second approximation you'll want to interpolate between the equinox and solstice and use that to approximate an allowance for the ~24 degree tilt of earths rotation axis. That second approximation error is there for all times that are not midday, but reduce to zero as you approach midday. A third approximation might be to allow to the offset between your local timezone and solar midday. Where I am (Sydney) we are fairly close to the middle of the +10 and +11 timezone boundaries, so solar noon is within a few minutes of timezones noon. Perth on the other hand is way out to the west of it's timezone, so solar noon there is almost 25 minutes off from timezone noon. So "watch north" in Perth will be about 7.5 degrees off "true north".