A.M. and P.M.

A.M. = ante meridiem
P.M. = post meridiem

Literally, "before-mid-day" and "after-mid-day"

Okay, so is 12 a.m. midnight or noon? I think most people would say midnight, and I agree that 12 and one second a.m. is one second after midnight. But I think the moment of midnight itself should be 12 p.m., because it is the last number in the counting series of post meridiem hours.

ante meridian (before noon)
post meridian (after noon)

Equus, this is an old puzzle. Midnight is both 12 p.m. and 12 a.m., while noon is neither, since it is "m." itself. Maybe that's why the military use 2359 to mean midnight at the end of the evening on a stated day, and 0001 to mean midnight at the start of a new day.

a long thread there
http://www.able2know.com/forums/viewtopic.php?t=30773

Holy Crow!! People in these forums just seem to like to hear themselves talk (I might qualify by posting this). Why did anyone post after the first person answered the question perfectly? Especially saranac74 ... he/she obviously didn't read what was posted before :Op

I thought I was having deja vu.


The solution is to write 12:OO M for midnight and 12:00 N for noon.



Joe

In the twelve-hour system, the abbreviations AM and PM mean, respectively, ante meridiem (before noon), and post meridiem (after noon). Thus 12:01 PM is 1 minute after noon, and 12:01 AM is 1 minute after midnight. In English-language IBM manuals, AM and PM are not used in connection with midnight and noon; instead, noon (or 12 noon), and midnight (or 12 midnight) are used. The meaning of 12:00 is undefined and remains ambiguous.

In the ISO/IEC twenty-four-hour system, 24:00 is midnight at the end of a day, and 00:01 is one minute after midnight of the next day. The sequence is 23:59, 24:00, 00:01. In ISO/IEC standard 8601, both 24:00 and 00:00 are allowed to indicate midnight, with 24:00 indicating the end of the day and 00:00 indicating the start of the next day.

I agree 100% "noon" and "midnight" should be used instead of "12 a.m" or "12 p.m" which are ambiguous.

However ambiguous 12:00 is, in daily life here in the US, 12 a.m. is used to indicate midnight, and 12 p.m. to indicate noon. This is often seen on invitations/announcements, and on digital clockfaces. I think it is true on my a2k and computer desktop pages as well.