Figure 16-5.  Time zones in the conterminous United States.  flying eastward from one time zone to another, or perhaps  even when flying from the western edge to the eastern edge  of the same time zone. Determine the time of sunset at the  destination by consulting the flight service station (FSS) and  take this into account when planning an eastbound flight.  In most aviation operations, time is expressed in terms of  the 24-hour clock. ATC instructions, weather reports and  broadcasts, and estimated times of arrival are all based on  this system. For example: 9 a.m. is expressed as 0900, 1 p.m.  is 1300, and 10 p.m. is 2200.  Because a pilot may cross several time zones during a flight, a  standard time system has been adopted. It is called Universal  Coordinated Time (UTC) and is often referred to as Zulu  time. UTC is the time at the 0° line of longitude which passes  through Greenwich, England. All of the time zones around  the world are based on this reference. To convert to this time,  a pilot should do the following:  For Daylight Saving Time, 1 hour should be subtracted from  the calculated times.  By using the meridians, direction from one point to another  can be measured in degrees, in a clockwise direction from  true north. 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 that this line forms with  a meridian. Direction is expressed in degrees, as shown by  the compass rose in  Figure 16-6.  Because meridians converge toward the poles, course  measurement should be taken at a meridian near the midpoint  of the course rather than at the point of departure. The course  measured on the chart is known as the true course (TC). This  is the direction measured by reference to a meridian or true  north (TN). It is the direction of intended flight as measured  in degrees clockwise from TN.  As shown in  Figure 16-7,  the direction from A to B would be  a TC of 065°, whereas the return trip (called the reciprocal)  would be a TC of 245°.  16-5  Measurement of Direction  Eastern Standard Time ..........Add 5 hours Central Standard Time ..........Add 6 hours Mountain Standard Time.......Add 7 hours Pacific Standard Time...........Add 8 hours 105°  120°  90°  75°  Mountain standard time  Central standard time  Eastern standard time Pacific standard time 