I would point out that the sun is not always moving 15" in azimuth per second of time as some have said here. It is moving the quickest in azimuth when transiting the meridian, and that is definitely not the best time to observe for several reasons. The lower the sun gets to the east (when rising) or west (when setting), the slower it appears to move in azimuth. In my experience/opinion, unless you are using an instrument with dual compensators, or carefully level up using the bubble, the mislevelment of the instrument can be the largest error source, and is not removed by D/R observations. This also is affected to a larger degree when the sun is higher (m*Tan V), where m is mislevelment in seconds and V is the vertical angle.?ÿ?ÿ
Here are some velocities in azimuth for my location Pittsburgh today...
just after sunrise: 9.6"/s
mid morning: 9.7"/s (30?ø above horizon)
later in the morning: 10.9"/s (40?ø above the horizon)
near local noon: 40.7"/s (69.5?ø above the horizon)
near sunset: 9.6"/s
That is why observations on Polaris at elongation are easy to do because the star is hardly moving in azimuth for several minutes, and time is not critical.?ÿ
If you ever observe the moon you will notice that, depending on where it is, it can appear to really be moving, due not only to earth rotation but also the moon in its ~28 day orbit.?ÿ
Whenever I've done solar's in the past I've used the hour angle method setting my timepiece out of Boulder, Colorado.?ÿ
I was reading the link above about the Altitude method (something I've never used) and I was thinking it would probably be better to use the stars if one would use the altitude method.?ÿ
What do you guys think?
