Figure 16-3.  World aeronautical chart. The standard practice is to establish a time zone for each  15° of longitude. This makes a difference of exactly 1 hour  between each zone. In the conterminous United States,  there are four time zones. The time zones are Eastern (75°),  Central (90°), Mountain (105°), and Pacific (120°). The  dividing lines are somewhat irregular because communities  near the boundaries often find it more convenient to use time  designations of neighboring communities or trade centers.  Figure 16-5  shows the time zones in the conterminous United  States. When the sun is directly above the 90th meridian, it  is noon Central Standard Time. At the same time, it is 1 p.m.  Eastern Standard Time, 11 a.m. Mountain Standard Time,  and 10 a.m. Pacific Standard Time. When Daylight Saving  Time is in effect, generally between the second Sunday in March and the first Sunday in November, the sun is directly  above the 75th meridian at noon, Central Daylight Time. These time zone differences must be taken into account  during long flights eastward—especially if the flight must  be completed before dark. Remember, an hour is lost when  Figure 16-4.  Meridians and parallels—the basis of measuring time, distance, and direction.  16-4   $^{ }$ $^{L}$o n $^{g}$i t u d e  L a t i t u d e  aatto orr  ° N N  6 0 ° N N  4 N N  3 0 ° N N  ° S S  ° S S  ° S S  ° S S  1 5 0 ° W 1 3 5 ° W W  1 2 0 ° W W  1 0 5 ° W W  9 0 ° °W W 6 0 0 °°W W  44 55 ° ° W W  33 00 °° W W  11 55 °° W W  PP r i mm e e  mm ee rr ii dd ii aa n n  90°N 90°N  ° N N  7 5 5° °W W 7 5 5 ° 1 5 EEqq uu 1 5 3 0 4 5 6 0