12点到底是 a.m. 还是 p.m. ？这么多年你搞清楚了吗？

很多人都知道“am”代表上午
“pm”代表下午
可是中午或者午夜12点是“am”还是“pm”呢?
脑子是不是突然卡壳了?
和小编一起搞清楚如何表达吧

首先我们认识一下12小时制

The 12-hour system divides the 24 hours of a day into two periods lasting 12 hours each. The first 12-hour period is designated as am. It runs from midnight to noon. The second period, marked pm, covers the 12 hours from noon to midnight.
12小时制将一天中的24小时分为两个时段，每个时段都有12小时。第一个12小时时段指定为am（上午）：从午夜开始到中午。第二个时段标为pm（下午），从中午到午夜。

The abbreviations am and pm derive from Latin:
am和pm是从拉丁语缩写来的

AM = Ante meridiem : Before noon
意思是在中午前

PM = Post meridiem : After noon
意思是在中午后

meridiem /mə'ridi:əm/ n.正午

Ante meridiem is commonly denoted as AM, am, a.m., or A.M.; post meridiem is usually abbreviated PM, pm, p.m., or P.M.

Ante meridiem通常会写成AM, am, a.m., 或者是A.M.
post meridiem会缩写为PM, pm, p.m., 或 P.M.

Like many other sources, timeanddate.com uses am and pm, but the other variants are equally correct and widely used.

大多数的时间书写，就像世界日期及时间网一样是使用am和pm的，但其他变体也同样正确并被广泛使用。

那么
中午12点、
午夜的12点
分别该怎么表示?

The main weakness of the 12-hour system is a widespread confusion about which abbreviation should be used for noon and midnight: neither moment can logically be identified as before noon (am) or after noon (pm). For example, the moment of midnight occurs precisely 12 hours after noon on the previous day and 12 hours before noon on the following day.

12小时制的主要缺点是人们普遍混淆了正午和午夜的缩写：从逻辑上讲，这两个时刻都不能被定义为正午之前(am)或正午之后(pm)。例如，子夜的时刻发生在前一天中午12小时后，第二天中午12小时前。

However, most digital clocks and most sources, including timeanddate.com, designate midnight as 12 am and noon as 12 pm. Although the precise moment of noon falls in neither category, the hour succeeding it, from 12:00:01 to 12:59:59, is clearly after noon.

然而，大多数数字时钟和大多数时间源，包括世界日期及时间网，都将午夜定为12 am，中午定为12 pm。虽然恰好中午的那个时间点好像哪个类别都并不属于，但从12:00:01到12:59:59的连续时间显然是在正午之后。

To avoid any confusion when referring to the precise moment of noon or midnight, we recommend using the designations 12 noon and 12 midnight instead.

为了避免在提到中午或午夜对准确时刻产生混淆，我们建议使用12 noon和12 midnight来代替。

所以

中午或正午 (noon) 通常叫做
12:00 p.m.
子夜或午夜 (midnight) 叫做
12:00 a.m.

美国国家标准与技术研究所
(National Institute of Standards and Technology，NIST)
给出答案：
meridiem 就是 noon，
正午十二点应该表达为12:00 noon ，
而午夜十二点可以表达为12:00 midnight，
以方便区分。

不过，
12:00 midnight 的用法也比较模棱两可，
因为它无法区分是某一天开始的午夜，
还是结束的午夜。
要想解决这个问题，
可以用00:00(zero o'clock)
来表示某一天开始的午夜。