Meridian Passage (Mer Pass, Local Apparent Noon)

Definition

At the instant of transit the body bears due north or due south, the altitude is at maximum, and latitude follows from zenith distance and declination without any need for exact time. Sun meridian passage is tabulated in the almanac as a GMT value at the Greenwich meridian; correct for longitude at four minutes per degree to get local timing. In practice the observer begins measuring a few minutes early and follows the sun until it stops rising.