Converting Local time to UTC

From The WB7TJD Wiki

^{Larry, WB7C}

You are a radio amateur, active on HF, making contacts across the country and around the world.  Very likely, you keep a log of your contacts and keep time in UTC, the worldwide Coordinated Universal Time.

There are ways of keeping track of the time, ranging from keeping two clocks on the wall, one set to local time and one set to UTC to memorizing the time conversion.

My Dad used to keep a 12-hour clock on the wall, with numbers 13 through 24 marked on the face of the clock alongside the 1 through 12, for 24-hour time.

I used to operate several times each week in the evening hours, so I became very familiar with the time conversion over a period of about six hours, and needed only glance at the local time at 7:14 PM and know at once that it was 0214 UTC tomorrow.  I sometimes fired up the rig at the other end of the day, at some time when I was not usually on, and I had to do some figuring!

A chart to convert local time to UTC

Here is a chart to convert your local time into Coordinated Universal Time, or UTC.  "UTC," by the way is derived from the French words for the English "Coordinated Universal Time."

Because we use Mountain Standard Time here in Arizona, my conversion will use Mountain Standard Time plus seven hours to arrive at UTC.

Midnight is 12 AM and noon is 12 PM.

12 AM or 0000 MST becomes 0700 UTC. Start of a new day locally, same day UTC.
01 AM or 0100 MST becomes 0800 UTC.
02 AM or 0200 MST becomes 0900 UTC.
03 AM or 0300 MST becomes 1000 UTC.  Pronounced Ten Hundred.
04 AM or 0400 MST becomes 1100 UTC.
05 AM or 0500 MST becomes 1200 UTC. 

06 AM or 0600 MST becomes 1300 UTC.
07 AM or 0700 MST becomes 1400 UTC.
08 AM or 0800 MST becomes 1500 UTC.
09 AM or 0900 MST becomes 1600 UTC.
10 AM or 1000 MST becomes 1700 UTC.
11 AM or 1100 MST becomes 1800 UTC.

12 PM or 1200 MST becomes 1900 UTC.
01 PM or 1300 MST becomes 2000 UTC.
02 PM or 1400 MST becomes 2100 UTC.
03 PM or 1500 MST becomes 2200 UTC.
04 PM or 1600 MST becomes 2300 UTC.
05 PM or 1700 MST becomes 0000 UTC tomorrow.

06 PM or 1800 MST becomes 0100 UTC tomorrow.
07 PM or 1900 MST becomes 0200 UTC tomorrow.
08 PM or 2000 MST becomes 0300 UTC tomorrow.
09 PM or 2100 MST becomes 0400 UTC tomorrow.
10 PM or 2200 MST becomes 0500 UTC tomorrow.
11 PM or 2300 MST becomes 0600 UTC tomorrow.

0000 UTC or 2400 UTC?

With regard to 0000 UTC and 2400 UTC, they are both the same point in time, but 2400 UTC is the end of today and 0000 UTC is the start of tomorrow.  So, because a log book usually only has one date entry per line and space for start and end times on each line, I would take some liberty to end something at 2400 today and start something new at 0000 tomorrow.

If a contact stretched past 2400, I just added those minutes to today, signing someone out at 2442 UTC.  It is understood that 2442 UTC is 0042 UTC the next day!

If someone else joined us after 2400, it would go into the log on a new line under tomorrow's date, after 0000 UTC.

Of course, if ever I forwarded that information to other people, I would convert my 2400+ times into the correct date and time!

International Date Line

There are 25 time zones around the world.  The International Date Line zig-zags across the width of the zone that is 12 hours removed from UTC, making some areas in the Western Hemisphere that are minus 12 hours behind UTC, and due north or south of other places in the Eastern Hemisphere that are plus 12 hours ahead of UTC.  Depending on which side of the line your point of view is taken, at midnight local time, it is the start of a new day today and tomorrow, or the start of a new day today and yesterday.  Or today is just getting started as today is coming to an end!

Here in Arizona, and in most places in the world, stations to our east are later in the day, while stations to the west are earlier.

As you cross the Date Line going west, it gets to be earlier and earlier in the day, but the date advances to tomorrow.  In this respect, the USA is behind most of the world, for we Americans are among the last people on Earth to experience today.  Especially up in Alaska, where we look upon the Russia of tomorrow!