The full forms of AM and PM come from Latin and are used to distinguish between the time periods of the day in the 12-hour clock system.
Full Form and Meaning
1. AM: Ante Meridiem
Ante: Before
Meridiem: Midday (or noon)
Together, AM means “before midday.”
It refers to the time from midnight (12:00 AM) to 11:59 AM, covering the late night and morning hours.
2. PM: Post Meridiem
Post: After
Meridiem: Midday (or noon)
Together, PM means “after midday.”
It refers to the time from noon (12:00 PM) to 11:59 PM, covering the afternoon, evening, and night hours.
12-Hour Clock System
The 12-hour clock divides the 24-hour day into two periods of 12 hours each:
The first 12-hour period (midnight to noon) is marked as AM.
The second 12-hour period (noon to midnight) is marked as PM.
This system is commonly used in countries like the United States, Canada, and others, as opposed to the 24-hour clock system, which does not use AM/PM.
Historical Origin
The terms AM and PM originated from the Latin language.
The Roman Empire used sundials to track time, which divided the day into two 12-hour periods based on the position of the sun:
The AM period started when the sun rose and continued until noon (the sun was at its peak).
The PM period began after noon and lasted until the sun set and midnight followed.
Key Points to Remember
1. AM (Ante Meridiem):
Midnight to before noon.
Commonly associated with nighttime and morning.
2. PM (Post Meridiem):
Noon to just before midnight.
Commonly associated with afternoon, evening, and nighttime.
3. The 12-hour system requires the use of AM and PM to avoid confusion, unlike the 24-hour system which does not.
By using AM and PM, the 12-hour clock system provides a clear distinction between the two halves of the day.