We commonly use A.M. and P.M. to express time, but do you know what these abbreviations stand for and how they originated? In simple terms, A.M. refers to the time before noon, while P.M. represents the time after noon. However, the history behind these terms is much more fascinating and rooted in ancient astronomical observations.
The Earth’s Rotation and the Concept of Day and Night
The division between A.M. and P.M. is closely tied to the Earth’s rotation on its axis. As the Earth rotates, the part facing the sun experiences daylight, while the other side remains in darkness, experiencing night. This cycle begins when the sun rises in the east, marking the start of the day, and ends when the sun sets in the west. At noon, when the sun is directly overhead, it marks the midpoint of the day, or what we refer to as afternoon.
How Ancient Civilizations Determined Time
In ancient times, people relied on the sun’s position to measure time. By observing the sun’s journey across the sky, they could roughly estimate the time of day. At night, stars were used as celestial guides for timekeeping. Over time, the concepts of A.M. and P.M. developed based on the sun’s position relative to an imaginary line in the sky known as the meridian.
What Is the Meridian?
The meridian is an imaginary line that runs from the North to the South in the sky. When the sun reaches this line at its highest point, it signifies noon. Before the sun crosses this line, it is morning, or A.M. (Ante Meridian). Once the sun moves westward after crossing the meridian, the time is classified as P.M. (Post Meridian).
The Latin Origins of A.M. and P.M.
The term “meridian” comes from the Latin word Meridies, which means “middle of the day.” The abbreviation A.M. stands for Ante Meridian, meaning “before the meridian,” while P.M. stands for Post Meridian, meaning “after the meridian.” These terms help us divide the day into two distinct halves: the morning (from midnight to noon) and the afternoon (from noon to midnight).
The Practical Use of A.M. and P.M.
In modern timekeeping, A.M. is used for the hours between 12 midnight and 12 noon, while P.M. covers the hours from 12 noon to 12 midnight. This simple system has been passed down through centuries, helping us accurately describe and manage time in our daily lives.
By understanding the origins and meanings behind A.M. and P.M., we can appreciate how ancient knowledge of the sun and the stars continues to shape the way we measure time today.
