The term "Meridian" taken from the celestial sphere gives its name to a.m. and p.m.
Here's why:
1. Meridian is an imaginary line that runs from the North Pole to the South Pole passing through the observer's zenith (the point directly overhead). This line marks the highest point the sun reaches in the sky.
2. The term "a.m." stands for "ante meridiem" in Latin, which means "before noon." When the sun crosses the observer's meridian, it is midday, marking the start of p.m. hours.
3. Conversely, the term "p.m." stands for "post meridiem" in Latin, which means "after noon." After the sun crosses the observer's meridian, it is afternoon, indicating p.m. hours.
Therefore, the concept of the meridian, representing the sun's highest point in the sky for an observer, gives rise to the terms a.m. and p.m. to distinguish between the hours before and after midday.
