Final answer:
When it's 12 noon at your location on the Prime Meridian, moving 15 degrees east or west will change the local time by one hour because the Earth rotates 15 degrees every hour. The Prime Meridian at 0 degrees longitude is the reference for Universal Time, and time differences are used to determine longitude. AM and PM indicate whether the time is before or after the Sun has crossed the local meridian.
Step-by-step explanation:
Understanding the concept of time zones and lines of longitude is crucial in geography. When it is 12 noon at your location and you are situated on the Prime Meridian, moving 15° to the east will place you in a time zone where it is 1 p.m., because that meridian faced the Sun an hour ago. Conversely, if you move 15° to the west, the local time will be 11 a.m., as the Sun will reach that meridian in an hour. This system continues every 15°, adding or subtracting an hour accordingly, because the Earth rotates 15° every hour. The Prime Meridian, defined at 0° longitude, runs through the Royal Observatory in Greenwich, England, and serves as the reference point for Universal Time (UT). If it is noon where you are and you have a clock set to Greenwich time, you can determine your longitude by checking the clock at the moment the Sun passes your local meridian. For example, if it is Greenwich time 3 p.m. when it's noon by your local time, you're located at 45° west longitude (15° for each hour difference). The distinction between AM and PM is that AM signifies the time before midday (ante meridiem), when the Sun has not yet reached the local meridian, while PM indicates the time after the Sun has crossed the local meridian (post meridiem).