Latitude from a sun altitude taken near (but not exactly at) meridian passage. Handy when cloud closes in at LAN.
Formula
$$ H_\text{mer} = H_o + \frac{\cos L \cos \delta (1 - \cos h)}{\cos(L - \delta)} $$
Symbol legend
| Symbol | Meaning | Unit | Source |
|---|---|---|---|
| $H_o$ | Observed altitude | ° | sextant |
| $δ$ | Declination | ° | Almanac |
| $L$ | DR latitude | ° | estimate |
| $h$ | Local hour angle | ° | Almanac + longitude |
| $H_\text{mer}$ | Adjusted meridian altitude | ° | derived |
Sources
- Bowditch - American Practical Navigator.