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Ex-Meridian Latitude

Latitude from a sun altitude taken near (but not exactly at) meridian passage. Handy when cloud closes in at LAN.

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Formula, assumptions, and limits

Hmer=Ho+cosLcosδ(1cosh)cos(Lδ)H_\text{mer} = H_o + \frac{\cos L \cos \delta (1 - \cos h)}{\cos(L - \delta)}
SymbolMeaningUnit
HoH_oObserved altitude°
δδDeclination°
LLDR latitude°
hhLocal hour angle°
HmerH_\text{mer}Adjusted meridian altitude°

Source: Bowditch - American Practical Navigator

In short

Latitude from a sun altitude taken near (but not exactly at) meridian passage.

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