AM and PM | Greenwich Mean Time
Greenwich Means Time to the World

A.M. and P.M.

What is Noon and Midnight?

A.M. and P.M. start immediately after Midnight and Noon (Midday) respectively.

This means that 00:00 A.M. or 00:00 P.M. (or 12:00 A.M. and 12:00 P.M.) have no meaning.

Every day starts precisely at midnight and A.M. starts immediately after that point in time e.g. 00:00:01 A.M. (see also leap seconds )

To avoid confusion timetables, when scheduling around midnight, prefer to use either 23:59 or 00:01 to avoid confusion as to which day is being referred to.

It is after Noon that P.M. starts e.g. 00:00:01 PM (12:00:01)

A.M. abbreviation ante meridiem

P.M. abbreviation post meridiem

Main Entry: an·te me·ri·di·em
Pronunciation:
"an-ti-m&-'ri-dE-&m, -dE-"em
Function: adjective
Etymology: Latin
Date: 1563
Meaning: being before noon
Abbreviation a.m.





 

Main Entry: post me·ri·di·em
Pronunciation:
-m&-'ri-dE-&m, -"em
Function: adjective
Etymology: Latin
Date: 1647
Meaning: being after noon
Abbreviation p.m.