What's the difference between AM and PM? You're really not the first world traveler to have to look it up again. It's a time indication that we're in here The Netherlands do not or hardly use it, so after a while you often forget it again. If you want to know what the difference is, then you are certainly not alone! In this article we explain exactly what the difference between AM and PM is, but we also give practical information about the countries that use it, and where the difference comes from.
AM is Ante Meridiem and is valid from 12 midnight to 12 noon. You can easily remember this by thinking of “After Midnight† The night starts at 12 o'clock in the morning. As long as your AM = “After Midnight” but remember you also automatically know what PM should be.
PM stands for Post Meridiem. In other words after the afternoon† It's not a disaster if you forget what it literally stands for. This time applies from 12 noon to 12 noon. You can easily remember that PM stands for "Pass Noon". This is the one thing you need to remember to never go wrong again!
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More handy mnemonics
- The letter A (from AM) occurs earlier in the alphabet than the P (from PM)
- AM = At Morning, then you know that everything else is PM.
- Bad morning (AM) and nice afternoon (PM)
Difference AM and PM – Why important?
This is mainly used in English speaking countries. In European countries, the 24-hour time format is used everywhere. When you read articles online to, for example, prepare your vacation, you may come across the time indications. When exactly does your flight arrive? It is useful to know when you will arrive, especially if you fly to different time zones. You will be the first (and not the last) to book a hotel on the wrong day because a mistake was made in the day in combination with AM and PM.
Where is the 12-hour format (AM and PM) used?
Most countries around the world today use the 24-hour system. However, the 12-hour format, including AM and PM, is officially used in only a few countries, including:
- United States
- Canada (except Quebec)
- New Zealand
Midnight / Midnight Confusion
Another source of confusion is the lack of a date stamp in the 12-hour system, which makes it impossible to logically identify an accurate time when only a date and noon (midnight) are specified.
Imagine being asked to pick up a friend from the airport at 13 noon on April 12.00. Would you go there between April 12 and April 13 at midnight? Or 24 hours later?
One way to solve this problem is to sacrifice accuracy for clarity. Your friend may ask you to be at the airport at 13:12 PM on April 01 or, if the following midnight is meant, 23:59 PM on April 13. Alternatively, the 24-hour format can be used. Here 0:00 refers to midnight at the beginning of the day while 24:00 is midnight at the end of the day.
Why does the day have 24 hours?
It is thought that the Egyptians are responsible for dividing the day into 24 equal parts. One story suggests that the Egyptians were fond of counting in base twelve (instead of base 10 commonly used today).
This is thought to be because they counted finger joints instead of fingers. Each of your fingers has three joints, so if you count by pointing your thumb at finger joints, you can count to twelve for each hand. This may seem arbitrary, but it's really just weird to count in base ten, simply because we have ten digits, digits that anyone ever made up.
The Egyptians divided the clock into 12 hours during the day and 12 hours at night (or alternatively 10 hours between sunrise and sunset, one hour for each twilight period, and 12 hours of darkness). This is known for several sundials from the period marked with hours. Interestingly, this means that hours started to change in length with the seasons (as the amount of daylight versus darkness changes).
Seen a mistake? Ask? Remark? Let us know in the comments!