To indicate a course to be followed in flight, draw a line on the chart from the point of departure to the destination and measure the angle which this line forms with a meridian. This makes a difference of exactly 1 hour between each zone.īy using the meridians, direction from one point to another can be measured in degrees, in a clockwise direction from true north. The standard practice is to establish a time zone for each 15° of longitude. Noon is the time when the sun is directly above a meridian to the west of that meridian is morning, to the east is afternoon. Since the day is divided into 24 hours, the Earth revolves at the rate of 15° an hour. A day is defined as the time required for the Earth to make one complete rotation of 360°. The meridians are also useful for designating time zones. Chicago is approximately 42° N latitude, 88° W longitude. Washington, D.C., for example, is approximately 39° N latitude, 77° W longitude. The arrows in the figure above labeled “Longitude” point to lines of longitude.Īny specific geographical point can be located by reference to its longitude and latitude. The 48 conterminous states of the United States are between 67° and 125° W longitude. The “Prime Meridian” which passes through Greenwich, England, is used as the zero line from which measurements are made in degrees east (E) and west (W) to 180°. Meridians of longitude are drawn from the North Pole to the South Pole and are at right angles to the Equator. Meridians and parallels–the basis of measuring time, distance, and direction.