What does am and pm mean,when did it come into effect?

Question

Since am and pm are used everyday pretaining to the time you'd think the answer would be easy to find.

Answer 1

The 12-hour clock is a timekeeping convention in which the 24 hours of the day are divided into two periods called ante meridiem (a.m., Latin from most idiomatic to most literal "forenoon" "before noon", "before midday", "before the middle of the day", "before the meridian", and "before the middle day") and post meridiem (p.m., Latin for "afternoon", "after noon", etc.) Each period consists of 12 hours numbered 12 (acting as a zero), 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11. The a.m. period runs from midnight (inclusive) to just before noon (exclusive), while the p.m. period runs from noon (inclusive) to just before midnight (exclusive). The most common convention is to assign 12 a.m. to midnight and 12 p.m. to noon, defining both half days to have a closed (inclusive) beginning and open (exclusive) end.


History and usage
The 12-hour clock originated in Egypt. However, the lengths of their hours varied seasonally, always with 12 hours from sunrise to sunset and 12 hours from sunset to sunrise, the hour beginning and ending each half-day (four hours each day) being a twilight hour. An Egyptian sundial for daylight use[1] and an Egyptian water clock for nighttime use found in the tomb of Pharaoh Amenhotep I,[2] both dating to c. 1500 BC, divided these periods into twelve hours each. The Romans also used a twelve-hour clock: the day was divided into twelve equal hours (of, thus, varying length throughout the year) and the night was divided into three watches.

The Romans numbered the morning hours originally in reverse: for example, "3 a.m.", or 3 hours ante meridiem meant "three hours before noon", compared to the modern meaning of "three hours after midnight".

Early medieval clock faces used the 12 hour numbering scheme (using Roman numerals), but showed both a.m. and p.m. sequences simultaneously. This is known as the Double-XII system, and can be seen on surviving medieval clock faces, such as those at Ottery St Mary, Wells, and Venice.

Today, most analog clocks use the 12-hour clock dial, where the hour hand (shorter and sometimes thicker) commonly rotates once every 12 hours. These are used even in cultures where the 24-hour notation is otherwise preferred. Some 12-hour dials show the numbers 13 to 23 written inside the primary 1 to 12 ring.

Although it has largely been replaced today by the 24-hour notation around the world, especially in written communication, the 12-hour notation with a.m./p.m. suffix is common in some parts of the world.

Answer 2

I can't tell you when it came into effect, but Am and Pm stand for Ante Meridian and Post Meridian. They are based on when the Prime Meridian, Zero degrees longitude is closest to the sun. So AM is when you are heading toward high noon and PM is when you are past high noon.

Answer 3

Am Pm Stand For

Answer 4

AM = ante meridem
PM = post meridem

The meridem, or "meridian," is an imaginary line that divides the sky into two hemispheres. During the AM the sun is "ante meridem," or before (east of) the meridian; in the PM the sun is "post meridem," or after (west of) the meridian.

Answer 5

Ante Meridian and Post Meridian. The meridian is considered to be the point when the sun has reached its highest point in the sky. It actually varies over the year, but noon is accurate enough.

Answer 6

AM means ante meridian and PM means post meridian, this originates from Latin, meaning before midday and after midday.
First referred to in english literature in about 1883.

Answer 7

AM=aftermidnight, PM=postmidnight. N=noon

Answer 8

After Midnight, Post Midnight.

Answer 9

ante meridian and post meridian. It came into effect after the establishment of Greenwhich mean time.

Answer 10

We see in the Acts of the Apostles that they met both on Saturdays and Sundays but Sundays became the main day to commemorate the Lord's Resurrection which we consider the Christian Sabbath and the reason for our beliefs and salvation . This does by no means negate our obligation to obey the commandments for by obeying the third commandment we attend Liturgy on the Christian Sabbath which goes from sunset on Saturday night to sunset on Sunday night like the Jews from Friday night to Saturday night at sunset.