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Latitude and Longitude The Earth is a sphere, and in order to know our location on it, it has been divided it up into a pattern of intersecting lines called the graticule: Those running north to south are called "meridians" or lines of "Longitude" Those running East and West are called "parallels" or lines of "Latitude" So to identify your location on Earth, we can use a coordinate as an intersection of Latitude and Longitude Latitude is measured in degrees, minutes and seconds from the Equator (0 degrees) to the poles (90 degrees N or S) while Longitude is measured in degrees, minutes, and seconds from the Prime Meridian (0 degrees) in Greenwich England to 180 degrees at the International Date Line. There are 60 minutes in a degree, and 60 seconds in a minute. Time in Aviation The Earth rotates about its own axis, and therefore time is very different at different places on earth based on their longitude. To provide a convenient method of measuring time an imaginary sun called the "mean sun" is assumed to travel at a uniform rate of speed throughout the year. The interval between two successive transits of the mean sun is called a "mean solar day" The mean solar day is divided into 24 equal hours The mean time on any particular meridian is called the "Local Mean Time" (LMT} for universal reference, a standard time has been established, known as "Coordinated Universal Time" (UTC) It is also known as "Z time" or "Zulu time" In aviation, in order to be clear, times are most commonly referenced and reported in UTC (including by ATC and on weather reports) UTC is the local mean time at the Prime Meridian The LMT of a place East of the Prime Meridian will be ahead of UTC The LMT of a place West of the Prime Meridian will be behind UTC Definitions Heading - is the direction the aircraft is pointing Bearing - is the angle (clockwise) between North and the direction to an object or location Relative Bearing - the angle (clockwise) between the aircraft's heading and an object or location Track - is the actual path of travel of the aircraft over the ground Course - is the desired or planned path of travel of the aircraft Drift - is caused by wind and is the angle between the aircraft's heading and its track Wind Velocity - is the direction and speed of the wind Airspeed - is the speed of the aircraft relative to the air it is flying through Groundspeed - is the speed of the aircraft relative to the ground