Answer: Longitudes determine the current time of one location compared to the current time of other locations.
Explanation: To be able to standardize time around the world, diplomats considered the following:
- The Earth is a sphere. Therefore, when it rotates, it rotates 360º.
- Those 360º can be divided evenly into 24 hours and make 15º per hour.
- In other words, for every 15º of rotation, one hour passes.
The world was consequently divided into longitudes of 15º for every hour - time zones. Time zone 0 was the Greenwich Meridian. Every longitude to the east of the Greenwich Meridian is +1 time zone. Similarly, every longitude to the west of the Greenwich Meridian is -1 time zone.
As a result of the establishment of time zones using longitudes, times in different locations can be compared to one another. To illustrate, when a friend in New York says, "Let's call at 8:00 AM my time," to his friend in Los Angeles, the friend in Los Angeles can object and say, "8:00 AM Eastern Standard Time is 5:00 AM Pacific Time. I'm sleeping then, you inconsiderate baboon!"