A few days a go there was a discussion initiated by Steve L. about a swivel mounting. I posed a question about properly aligning the north/south tilt of a dial. There seemed to be little interest in this, but I feel obliged to post the answer as promised. The .gif attachment has the math and the derivation for anyone who is interested. It works only for sundials that measure right ascension (hour angle), such as common horizontal and equatorial dials. It works well near the solstices, but runs into errors if measuremets are done near the equinoxes. I think it could be tidied up a bit, but I don't have the energy or time to do that right now.
The truth is that it is not such an important adjustment to worry about. A north south tilt error of 2 degrees would produce a maximum error of just under 4 minutes near the solstices, and virtually no error at the equinoxes. Compare that to an east/west roational error of 2 degrees, which would cause a nearly 8 minute error (at 40 degree latitude, winter solstice, noon). This sort of stuff interests me. Bill Gottesman Burlington, VT 44.4674 N, 73.2027 W ps If anyone would prefer a more legible .dxf of this graphic, let me know. Attachment converted: Macintosh HD:NS ERRORS.gif (GIFf/JVWR) (00015425)
