Sorry, but there was a typo in my most recent post. I didn’t want to bother you with this, but I also didn’t want to leave the typo un-corrected.
In the two paragraphs quoted below, in quotes, “h” should be replaced with “Az”: “Of course, during the negative-declination half of the year, the sun is always south of the east-west line, and h is always reckoned with respect to south. “But, during the positive-declination half of the year, of course there's part of the day when the sun is north of the east-west line. At those times, the Time-Altitude formula's h answer is with respect to north instead of south.” - --------------------------------------------------------------- At least as I use TA, both h and Az are always positive, whether they’re east or west of the north-south line. h has its usual meaning, reckoned from the meridian that crosses the south horizon-point, but Az is meant with respect to, measured from, south if the sun is south of the east-west line, and from north if the sun is north of the east-west line. In the northern hemisphere, in the north-declination half of the year, it would be necessary to know which side of the east-west line the sun is on. That is accomplished by calculating when the sun crosses the east west line. I’ll state that formula again: cos h = tan dec/tan lat. …evaluated (or estimated) once for any day when TA or AW will be used. As I said, I just didn’t want to leave the typo un-corrected. By the way, TA isn't very popular with navigators and surveyors, though they mention it, and maybe sometimes use it. That's because of the error-vulnerability introduced by the measurement of the altitude. And, when you're walking, or in a car, and don't have the opportunity to actually *measure* sec Alt or tan Alt, then that can make an error of a magnitude that matters some when hiking. But TA is simpler and briefer than the Time method (that's the familiar formula for azimuth, making use of time, latitude and declination) or the Altitude method (making use of altitude, latitude and declination), and lends itself to the convenient Altitude Watch method. Of course if you just want to know which direction is which, along a street, then you don't need great accuracy. Any determination is useful if you know or assume that it isn't off by 90 degrees (if, for example, all you need to know is which way on this street is south). Michael Ossipoff
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