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CHAPTER 5
Basics of Time
Introduction
In this chapter you will be introduced to the basics of time. You may be
asking yourself what part time plays in the practice of navigation. You
may be surprised to find out how important time actually is. For
example, when we use time to mark the exact second of celestial
observation an error of a few seconds could result in a fix error of many
miles from the correct fix position.
Objectives
The material in this chapter will enable the student to:
Define the terms apparent and mean solar time.
Match the following kinds of time with their definitions:
a. Greenwich mean time (GMT)
b. Universal time (UT)
c. Local mean time (LMT)
d. Zone time (ZT)
e. Zone description (ZD)
State why standard time zones are used and how they are measured.
Calculate ZD from ship’s longitude.
State the procedures for adjusting a ship’s time and date at sea.
Convert ZT to GMT.
Convert GMT to ZT.
Identify the equivalent values for arc and time.
Convert time to arc and arc to time manually.
Convert arc to time using The Nautical Almanac.
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