Celestial navigation glossary
Date line
The 180th meridian, where zone descriptions +12 and −12 meet: crossing it westward, the ship's calendar jumps a day forward.
Where the course teaches it
Crossing the date line, in the module Angles, time and UT. Convert between arc and time, and turn zone time into UT.
Taught alongside it
- Universal Time (UT)
- The time at Greenwich, used for every almanac lookup.
- Zone description (ZD)
- Hours to add to zone time to get UT: +5 in the US east coast winter zone, for example.
- Watch error
- How fast or slow the watch is against UT. Each second of time is 15″ of longitude.
- Watch rate
- How much the watch gains or loses a day, used to work out the error since the last time check.