Part IV · The fix · Page 6 of 6
Penciling in the planets
The stars keep their places on the base for years. The planets wander along the zodiac, so every navigator marks them in pencil before a passage and rubs them out when they have moved. All it takes is the almanac and one subtraction.
- SHA of the planet = GHA of the planet − GHA ♈︎, both from the daily page for the same time (0h UT is fine). Add 360° if it comes out negative. The almanac also lists each planet’s SHA at the foot of the stars column.
- The rim reading is 360° − SHA. (The base is laid out by 360° − SHA, which astronomers call right ascension.)
- The declination is on the same daily page. Go out from the center to it along the line to that rim reading: the dashed circles are every 30°, and the equator is the solid one.
- Mark it with a small cross and the planet’s name, in pencil.
Jupiter, March 10, 2027, 0h UT. GHA Jupiter 25°54.3', GHA ♈︎ 167°27.0', Dec N 16°13.0'.
SHA = 25°54.3' − 167°27.0' + 360° = 218°27.3'.
Rim: 360° − 218°27.3' = 141°32.7'. Out to N 16°13.0', and mark it.
How often? Jupiter and Saturn move a few degrees a month, so one plot does for a passage. Venus and Mars move faster: re-plot every couple of weeks. The Moon moves about 13° a day, so it is never penciled in.
Try it
October 30, 2026. From the daily page, at 0h UT: GHA Saturn 28°37.3', GHA ♈︎ 38°19.7', Saturn’s declination N 1°15.4'. Pencil Saturn onto the star base.
degrees and minutes, like 51 35.6
degrees and minutes, like 51 35.6
- Find that reading on the rim, then go in toward the center (or out) to the declination, using the dashed declination circles, and tap the base to pencil it in.