Michael Hotka's
Activity 14 - Location - Measure Your Local Latitude Results

Clocks weren’t accurate enough to do this during our time period but its easy and fun to do

1. Note the clock time as the Sun crosses the meridian you’ve established in prior activities. Convert it to UT. Determine your longitude based on the time difference between local noon at the Greenwich, UK Observatory (0.000 degrees and 12:00 p.m. assuming no equation of time correction) and that the sun moves at 15 degrees/hr (mean solar time). The same equation of time correction would apply to both, so it can be ignored.

2. Before the ability to find longitude sea travel involved sailing until the correct latitude was reached and then sailing east or west to the destination. It made voyages much longer and dangerous. It wasn’t until after Harrison’s invention of the marine chronometer in 1761 that longitude determination became practical. Even then it took years for the practice to become established. It was extremely important for the clock to be set to the correct time. Ships headed down the Thames would set their clocks by watching for the time ball to drop every hour at the Greenwich Observatory. The ball still drops but primarily for the visitors at the Observatory. There is an excellent book & video called Longitude that details Harrison’s efforts to develop the marine chronometer.

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