NavList:

Bill Lionheart, you wrote:
"I suppose a practical use is we want to understand what navigational stars we might be able to use at dawn/dusk. Presumably the procedure is that you find a star near your zenith at a specific time and location and then pop a ring on the sphere of a suitable radius for your horizon (or a sensible altitude above the horizon)."

The best procedure for setting a star globe to the proper orientation is to set it for sunrise or sunset. This suggests that the ecliptic, labeled with dates, should be required on a star globe. Of course we set by latitude based on tilt relative to the local horizon (altitude of Polaris equals latitude or dec below pole touching the horizon should be 90-lat). Then the orientation in hour angle follows by placing the Sun on the horizon. The clock time of the event might be known or calculated, but do we really need it? For example, suppose I want to shoot stars in evening twilight, and I want to plan ahead. I can place the Sun right on the horizon using the ecliptic on a star globe, and then I can rotate the globe 7.5° more to advance to half an hour after sunset. Then I can read off those approximate directions and altitudes. Assuming this is tonight and my latitude is 53°N, I would be able to read off altitudes and azimuths to the nearest 5° (easily to 5°) as follows: Vega azm 290° alt 35°, Capella azm 65° alt 40°, and maybe Diphda azm 165° alt 20°. I could put a dot for Venus on the globe, too, if I have current almanac data, but Venus is easy to find even before sunset. I don't really need a star globe for that.

Frank Reed