A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Tibor Miseta
Date: 2021 Mar 4, 09:48 -0800
"why do you mark the stars (transparent) overlay for latitudes?"
Because they are different for each latitude! For better readability the starwheel is clipped to the range of visible stars only (plus some margin), and magnified to fit into the available working space. This makes all of them different. I attach a Lat 60N version, you will see the difference immediately (the very last page shows if it were built together).
"The fact that the end of the declination scale points to 165° is irrelevant, right?"
Exactly! Its more natural position would be at 0°or 180°, but at those positions it would mess up either the analemma or the altitude marks, none of them would be readable. It disturbs the less here (or may be around 195°), although it somewhat messes the 350°azimuth. But there are big trees in this direction preventing the free view, so I could sacrifice it easily.
"the Analemma's axis is aligned with the local meridian - pointing to 180°, right?"
The analemma's position is in relation with the date scale, and they are rotated together that the equinoxes are at 0° and 180° (approximately, see later). This way if you rotate the index to a selected date, the ecliptic will intersect the analemma at the Sun's midday (12.00 UT) position. With the same settings the arrow of the index on the hour angle scale will show the approximate GHA of Aries at 00:00 UT on the same day. (The error varies from year to year in the range of +/- 0.4° and is not constant around the scale.) I still need to figure out the best aligmnet that would produce the less average error. But this is good enough to set up the planets and the Moon for this application.