The real books · Page 4 of 5
Pub. 249 Vol. 1: the selected stars
Vol. 1 is built for one job: the twilight star fix. It is entered with just two numbers, your AP latitude and LHA Aries, and gives seven stars, chosen because they are bright and well spread round the horizon at that place and moment. For each it gives Hc, and the true bearing Zn directly: no Z rules, no declination, no Table 5.
LAT 35° N. Three rows: each is 1° of LHA Aries, about 4 minutes of time. ◆ marks the three for a quick fix. The table scrolls sideways.
| LHA Aries | ◆ Kochab | ◆ REGULUS | PROCYON | SIRIUS | RIGEL | ◆ ALDEBARAN | CAPELLA | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Hc | Zn | Hc | Zn | Hc | Zn | Hc | Zn | Hc | Zn | Hc | Zn | Hc | Zn | |
| 120 | 30°09′ | 018 | 52°35′ | 120 | 59°50′ | 190 | 35°23′ | 202 | 32°01′ | 230 | 41°25′ | 261 | 57°49′ | 302 |
| 121 | 30°24′ | 018 | 53°17′ | 121 | 59°41′ | 192 | 35°04′ | 203 | 31°23′ | 231 | 40°37′ | 262 | 57°08′ | 302 |
| 122 | 30°39′ | 018 | 53°59′ | 122 | 59°30′ | 193 | 34°44′ | 204 | 30°44′ | 232 | 39°48′ | 263 | 56°26′ | 302 |
The printed volume makes its own choice of seven stars for each row; these are chosen by this course’s rule (bright, 15°–70° high, spread round the horizon), for practice in reading the layout. Positions for 2026-10-15.
Reading it
- A section for each degree of latitude, north and south, with a row for every degree of LHA Aries.
- LHA Aries = GHA Aries ± your AP longitude (east +, west −), with the AP longitude chosen so the minutes cancel, as for any body. The almanac gives GHA Aries.
- Star names in capitals are the brightest. ◆ marks the three that give the best three-star fix: shoot those first.
- The altitudes are true, not observed: correct your sextant altitudes for index error, dip and refraction (the stars column of the altitude corrections) before comparing.
Planning with it
It doubles as a star finder. Before twilight, work out LHA Aries for the time you plan to start, read the row, and preset the sextant to each star’s Hc; face its Zn and sweep the horizon. Each row down is 1° of LHA Aries, about 4 minutes later. Compare Planning a twilight fix: Choosing the stars in the course.
Its limits
- Only those seven stars. For any other star, a planet, the Sun or the Moon, use Vols. 2 and 3.
- It ages. The stars drift slowly against the sky (precession and nutation), so each edition is computed for an epoch and is meant for about five years. A small table corrects the fix for the years either side; left out, the error stays within a couple of miles over the edition’s life. Use the edition for the year you are in.