This B.A. thesis deals with the topic "Chronometer and time in astronomical navigation". The first part of the work refers to a chronometer and it deals with history, construction, handling and other chronometer related activities. There was a problem of determining the latitude of ship position on sea until a chronometer invention, which is being studied from the historical point of view in this work. Part of work about the chronometer construction depicts Spring Tension Chronometer and Quartz Chronometer. After that, maintenance procedures, suitable location on ship for this instrument and various influences affecting the chronometer are depicted. Finally, the method of determining the chronometer condition and the chronometer logging procedure is described. The second part deals with time in astronomical navigation. It deals with the concept of time, history of time measurement, time equation, and time zones. In addition to the theoretical part, the second part of the work involves several mathematical examples of time conversion and determination of longitude in astronomical navigation.