Obviously one minute after midnight is 12:01 AM.  But is midnight
12:00 AM or 12:00 PM?

Hi there!

Midnight is...midnight.  It is neither AM nor PM!

At least, that's what the Random House Dictionary of the English
Language (2nd Edition) and several other sources say:

"The period from midnight until noon is a.m. One minute before noon is
11:59 a.m. One minute after noon is 12:01 p.m. Many people distinguish
between noon and midnight by saying 12 noon and 12 midnight. Noon and
midnight are neither a.m. nor p.m."

"Boston Public Library FAQ"
[ http://www.bpl.org/research/telref/faqs.htm ]

"GreenwichMeanTime.com"
[ http://greenwichmeantime.com/info/noon.htm ]

"Useless Knowledge.com"
[ http://www.uselessknowledge.com/explain/time.shtml ]

"Time Questions and Answers from NIST"
[ http://physics.nist.gov/News/Releases/questions.html ]

"Where Do Noon And Midnight Fall?"
[ http://www.freewarenet.com/features/12am-pm/ ]

Perhaps this is why the military uses the 24 hour clock - to avoid
confusion?

Best regards!

missy-ga

Thank you.  However I find it discomforting that humanity can't get
together to simply agree that midnight will be called 12 AM (or 12 PM)
regardless of what AM and PM technically mean.  I would prefer
midnight to be 12 AM so that when the eleven changes to a twelve on a
clock, the PM would change to AM at the same time and not an
infintessimally small moment later.  The people who make alarm clocks
and computers need to be notified that they are incorrect at
indicating the time at noon and midnight!

a.m. is an abbreviation for Ante Meridiem (before noon,)the passage of
the sun through the local meridian, and so Midnight, 12 hours before
that event, is 12:00 a.m. It logically follows that midday becomes
12:00 p.m., a practice universally used when publishing train, buses
and airline time tables.

Translating it out makes it seem that it less "logically follows...":
12:00 p.m. equals 12:00 post meridiem equals 12:00 after noon - which
might not seem synonymous with Noon. The original answer seems best.

It may be hard to assign "P.M." to Noon, but it becomes easier to
understand if you think that very few events happen at 12:00:00.0000
exactly. If you assign "Noon" to mean the specific moment at midday
that all three hands of the clock are straight up, then the first
fraction of a second after noon is, by definition, after noon and
well-qualified to be called P.M. 11:59:59.99 (ad infinitum with those
9's) is clearly before the Noon moment, and therefore well-described
as A.M.

An accurate-to-the-second digital clock will read "11:59:59 AM"
followed next by "12:00:00 PM" because during the one-second period
"12:00:00 PM" is on the display, that "Noon moment" has already
passed.

Missy's answer is exactly correct, I think.

I would also claim that in common usage, by convention, midnight is
12:00 AM and noon is 12:00 PM. Partly this is for the reason that
lostcluster gives. But also, again by convention, midnight is the
point at which the date advances. If midnight were called 12:00 PM,
two disjoint portions of a single day would both be "PM". I suppose
there is no reason this could not be the case, except that it would be
even more confusing.

Obviously the 24 hour, 00:00 - 23:59, clock is superior. But in a 12
hour system, it would make a lot more sense to me if midnight and noon
were called 1:00. We start counting at 1, after all.

In response to blossom's comment:
 
"Obviously the 24 hour, 00:00 - 23:59, clock is superior. But in a 12
hour system, it would make a lot more sense to me if midnight and noon
were called 1:00. We start counting at 1, after all."

I would definitely agree with you that 00:00 - 23:59 is superior.

I would bring to your attention, however, that '12' takes the place of
'0' in the twelve hour clock.  Because in many cases, we don't start
counting at 1 (and IMO, in others, we do but shouldn't).  Notice the
inconsistency with starting a 1:00.  The hour would start a 1, but the
minutes would start at zero.  It's best to think of the 12 as a zero. 
This leads to a consitent counting of how many hours and minutes _have
passed since_ midnight or noon.

My own idiosyncratic, contrarian opinion is that our calendar should
work this way, too.  Rather than counting from the _1st_ day of the
_1st_ month (counting ordinally) I think we should write the date of
New Year's Day as 00/00/year, zero months and zero days having passed
since the beginning of the year.  Actually, I really think we should
write New Years as year.00(month).00(day) to be consistent about
having larger denominations on the left.

Then comparing dates would be easy and uniform, just a matter of
subtract numbers!  Unfortunately it would require re-writing all
reference material, oh well.

The convention 12AM for noon and 12PM for midnight has a little twist:

12 AM < 1 AM

For me, it is more "natural"  12PM for midnight.

" If midnight were called 12:00 PM, two disjoint portions of a single
day would both be "PM".

I do not see the point here, the day starts just after midnight.

I must admit to considerable amusement at the discussion here.  Not
that I find it silly - quite the contrary - but because, being a
chronic insomniac, it's never made a difference to me whether one is
AM/PM/whathaveyou.

Time just runs all together for some of us.  You folks that can tell
the difference are lucky.

missy-ga

There is an International Standard for Date and Time. It is known as
ISO 8601.

It defines the length of the second, minute, hour, day, week, month,
year, and so on.

It defines date formats like:
YYYY-MM-DD, Year-Month-Day
YYYY-DDD, Year and DayOfYear
YYYY-Www-DD, Year-WeekOfYear-DayOfWeek

It uses the 24-hour format for clock time, and defines the Base Time
Zone as being UTC (previously known as GMT).

The ISO 8601 Standard has been adopted in ALL Western nations, as well
as by most of the rest of the world (see ANSI X3.30 and NIST FIPS 4-1
in the US, CSA Z234.5 in Canada, EN 28601 in Europe, JIS X 0301 in
Japan, etc).


ISO 8601 has been adopted as RFC 3339 for use on the Internet.