I started taking for granted that most people were like pilots, able to understand the 24-Hour Clock and Universal Time. I, unfortunately, was mistaken and so therefore present:
My little primer on converting your time to everyone else's time. Or, AM/PM to GMT Instructions.
When I was in first grade, I was taught to tell time as 1 o'clock in the morning and two-thirty p.m. When my mom became a travel agent, I learned to tell time as 0100 and 1430. I also think I learned what "AM" and "PM" stood for (ante and post-meridian, before and after the half of the day). Fascinating, :p lets move on.
Exercise 1= Converting AM/PM to 24-Hour
24-Hour Time (otherwise known as Military Time) is written as 4 digits. The first two digits represent the hours (00 - 24, since there are 24 hours in the day, go figure), and the last two represent the minutes. There are 60 minutes in every hour, the world around. The first twelve hours relate directly to AM time. Therefore, 0800 is 8 o'clock in the morning, 8:00 AM. So, just put a colon in between the two sets of numbers, and you have you standard time format. However, to translate afternoon hours into your PM time, first take the hour digits and subtract 12. Then insert colon. If I gave you a time of 1855, that would work out to be 6:55 PM. (18-12=6) Get it?
Historical Factoid #429
In writing 24-Hour time, the leading zero is always added to make the four digits. Speaking the time is done in "hundred hours". So, 0900 is said as "oh-nine-hundred-hours", and 0430 is "oh-four-thirty", contemporarily known as "oh-dark-thirty".
1200 = The crack of noon, good time to wake up.
0000 and 2400 are the same time (Midnight). A common confusion is which is noon in the AM/PM format? (Military Time summarily solves this issue). 12:00 AM is Midnight, 12:00 PM is Noon. So please don't ask me to have lunch at 12 AM, I won't be hungry.
The Second Testament.
Now that you can write and tell time, what time is it where you live? I have no idea, but I can tell you what it is at my house, then give you a reference to figure out your own time. This idea is known as Univeral Time Coordinate, or UTC.
UTC, as a matter of fact, is located in Greenwich, England, the home of GMT, Greenwich Mean Time. Most written reports for aviators (Weather METARs, TAFs, most NOTAMs, etc) are referenced by UTC. This is done so anyone in the world can read the report, and calculate what time this would apply to them. However, sometimes the information is very regional, and thus time is given with the suffix "Local". For example, the sun sets in Los Angeles at 6:45 pm Local, or 1845 Local Pacific Time, or 0245 UTC. No, the sun didn't set at three different times during the day, just referenced three different ways.
There are, believe it or not, 24 distinct time zones in the world. The international dateline resides somewhere between Japan and Hawaii. England is precisely 12 hours either direction of that International Dateline (IDL). Accordingly, just to the left of Hawaii you'll find time beginning, and just to the right of Japan, you'll find time ending. It is quite possible to be standing on a boat, or perhaps hovering an aircraft, at the IDL with one pilot sitting in tonight, and the other pilot sitting in tomorrow! Now that's weird. Also strange, the world is truly round (not the stange part), science is exact, and yet the time zones were set by political means. Some parts of the world, though lying on the same longitude, are in several different time zones.
To calculate your local time from UTC, you'll need to know how many time zones you are away from England. California is 8 time zones before Greenwich, and New York is 5. So for right now, take a UTC time, say 0800 UTC to make it easy, and its 0000 PST, or midnight in San Francisco. Of course in New York its already 3 in the morning.
Even better, in the summer some of us get Daylight Savings, where some time zones get advanced by one hour. In this case, California is now just 7 time zones before England, represented as "-7", also the mathematical function to convert the time.
Appendix XXL. Why even bother?
Well, for one thing, human beings are not nocturnal. Our bodies function and react to sunlight. Therefore, it wouldn't be beneficial to tell everyone on the planet that it's 1 o'clock. Some would be sleeping while others are taking a lunch break. :laugh: This could get confusing if you move, say, a thousand miles to the east. You might lose your reference. So we each keep our own clock.
But to tell my buddy in Abu Dhabi that I'll call him at 6 pm, is that my time or his? For Abu, that would be like maybe 5 in the morning? How rude! But either way, I'd need to specify if that was 6 "my" time, or 6 pm "his" time. With no real way to know how many time zones away from me his is, I could tell him "I'll call you at 0200 UTC". In theory, stated above, he'll know what time to expect my call, even though I have no idea what his wristwatch is telling him. All I need to know is that I'm here in San Francisco, and that's -8 UTC. So I'll add 8 hours to 6 PM, and get 0200.
Btw, for you math freaks, time is calculated partly on a Base-24 count. If you add 8 hours to 1800 (above example), you get 2600, which doesn't exist. Subtract 24 from this number to get the correct time for the next day.
Final Test and Review.
I hope this helps. If not, hope it was fun to read!
Visit World Time Zones to figure out your place in the universe.
Until then, ta-ta! See you at 2100 UTC! :D
Oops! Totally forgot...
UTC and GMT are also known as Zulu Time, often written as 0930 Z.
Geeze, wrote all that and forgot the best part!