Everybody uses the expression “am” and “pm” lo indicate before noon and after noon. But do you know exactly what they mean, and how these terms came into being?
As you know. the turning of the earth makes the sun and the sars seem to move across the sky. Daylight, of course, begins when the sun rises in the east and ends when it sets in the west. When the sun is high in the sky, between these two positions, half of the daylight hours have been spent.
Therefore, by noticing where the sun stood in the sky, early man knew he could tell the time of day. At night, die motion of the stars served the same purpose.
The importer thing in keeping time is to know the exact moment of noon. for each of us, wherever we are, noon is when the sun is directly overhead. Think of an imaginary line, a meridian drawn across the sky stitching from the north point of you horizon down to die south point.
When the sun crosses your meridian, it is noon for you. While the sun is still east of this line or meridian, it is morning. After die sun has crossed meridian. So “am” is an abbreviation for ante meridian, or before midday. “pm” is the abbreviation for post meridian, or after midday. Each of the world’s time zones is about fifteen degrees wide in longitude, which is about the distance the sun moves through the sky. in an hour. Everyone who lives in the same time zone observes noon at the same moment. In tiffs way, the time differs by one hour as you move through each time zone.