Time signalA time signal is a visible, audible, mechanical, or electronic signal used as a reference to determine the time of day. Church bells or voices announcing hours of prayer gave way to automatically operated chimes on public clocks; however, audible signals (even signal guns) have limited range. Busy seaports used a visual signal, the dropping of a ball, to allow mariners to check the chronometers used for navigation.
Radio navigationRadio navigation or radionavigation is the application of radio waves to determine a position of an object on the Earth, either the vessel or an obstruction. Like radiolocation, it is a type of radiodetermination.
History of longitudeThe history of longitude describes the centuries-long effort by astronomers, cartographers and navigators to discover a means of determining the longitude (the east-west position) of any given place on Earth. The measurement of longitude is important to both cartography and navigation. In particular, for safe ocean navigation, knowledge of both latitude and longitude is required, however latitude can be determined with good accuracy with local astronomical observations.
Marine chronometerA marine chronometer is a precision timepiece that is carried on a ship and employed in the determination of the ship's position by celestial navigation. It is used to determine longitude by comparing Greenwich Mean Time (GMT) and the time at the current location found from observations of celestial bodies.
Time ballA time ball is a large, wooden or metal ball that moves up and down a pole, and which is dropped at a predetermined time of day. Because precise timekeeping is essential to the determination of longitude at sea, time balls were principally erected to allow navigators aboard nearby ships to synchronize their marine chronometers with a reference time standard controlling the ball.
TimeTime is the continuous progression of existence that occurs in an apparently irreversible succession from the past, through the present, and into the future. Time dictates all forms of action, age, and causality, being a component quantity of various measurements used to sequence events, to compare the duration of events or the intervals between them, and to quantify rates of change of quantities in material reality or in conscious experience.
Frame synchronizationIn telecommunications, frame synchronization or framing is the process by which, while receiving a stream of fixed-length frames, the receiver identifies the frame boundaries, permitting the data bits within the frame to be extracted for decoding or retransmission. When packets of varying length are sent, it is necessary to have an instantly recognizable packet-end delimiter (e.g., Ethernet's end of stream symbol).
Satellite navigationUse of satellite signals for navigation or geo-spatial positioning The US Space Force's Global Positioning System was the first global satellite navigation system and the first to be provided as a free global service.Asynchronous systemThe primary focus of this article is asynchronous control in digital electronic systems. In a synchronous system, operations (instructions, calculations, logic, etc.) are coordinated by one, or more, centralized clock signals. An asynchronous system, in contrast, has no global clock. Asynchronous systems do not depend on strict arrival times of signals or messages for reliable operation.
Time and frequency transferTime and frequency transfer is a scheme where multiple sites share a precise reference time or frequency. The technique is commonly used for creating and distributing standard time scales such as International Atomic Time (TAI). Time transfer solves problems such as astronomical observatories correlating observed flashes or other phenomena with each other, as well as cell phone towers coordinating handoffs as a phone moves from one cell to another.
SystemA system is a group of interacting or interrelated elements that act according to a set of rules or set of constraints to form a unified whole. A system, surrounded and influenced by its environment, is described by its boundaries, structure and purpose and is expressed in its functioning. Systems are the subjects of study of systems theory and other systems sciences.Frame synchronization (video)In video, frame synchronization is the process of synchronizing display pixel scanning to a synchronization source. When several systems are connected, a synchronization signal is fed from the synchronization source to the other systems in the network, and the video signals are synchronized with each other. A sync generator produces a central timing reference (usually a color black signal, also known as a black and burst) that is distributed throughout a facility.
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