I'll just offer an answer to the true north question. Instead of using Polaris, I would use the shadow method to find true north. To find the elevation of the celestial pole to use with an equatorial dial, you can derive this most easily by getting your latitude from a map.
The shadow method I prefer is to set up a stick in the ground so that it's perfectly plumb. Observe the shadow it casts at any time during the morning. Tie a string to the base of the stick, put a peg into the ground at the tip of the shadow and adjust the string (e.g. make a loop in the far end) so that it just reaches the peg. Using the loop and another peg, trace out an arc in the direction that the shadow will travel -- from northwest to northeast. Go away and come back in the afternoon. As the day wears on, the shadow will shorten until noon and then will begin to lengthen. At the same number of minutes PM as you took the reading AM -- for example 10:00 AM and 2:00 PM... or 10:00 and 4:00 during the summer -- the lengthening shadow will again cross the arc you traced out earlier. Actually you don't really have to trace out the arc if you have the string and peg ready for the second reading. If you mark the spot where the afternoon shadow is the same length as the string, you will then have three points: two pegs and the shadow-casting stick forming an angle. If you bisect that angle you will have a line pointing due north. Jack At 12:00 PM 10/3/99 -0600, rodandkellyheil wrote: > > Hello all, > > As a newcomer to this list, I beg your forgiveness if my questions have > already been hashed out on this list dozens of times. I have not been > lurking long enough to see what kinds of questions are appropriate. > > I am what you might call an "enthusiast." My wife calls me "obsessed." I > just have a very intense interest in sundials. > > My first question is What meridians require no longitudinal adjustment? In > other words, are time zones constructed so that the sun is directly over the > center of the time zone when the whole time zone is said to be at 12:00? I > live in the Rocky Mountain time zone, which seems to run from about 100 deg. > W. to 115 deg. W longitude. When it's noon here, is the sun directly over > 107.5 deg. W.? > > Secondly, how does one construct a gnomon for an equitorial sundial which > adjusts for the equation of time? > > Third, what clever ways have you discovered for pointing a gnomon at the > north star? I am wondering how I can aim it with precision when I can't > sight down the edge of it, as it is mounted on the base of my horizontal > sundial. > > Last, is there any significant difference between the north star and true > north, and do I need to adjust for this? > > Thanks in advance, > > Rod Heil > Enthusiast
