The Date/Time Conundrum

Previously, while we were in Maipiti, Mickey’s brother was searching the Internet for the time difference between Grand Junction and Maupiti.  He got two different answers.   Maupiti was either -3 hours behind or +21 hours ahead. Which is correct? The answer is that both can be correct in some ways but while we were in Maupiti neither was correct.  

How can this be?  Grand Junction is considered to be +7 hours Standard Time deviation from the Greenwich Meridian at 0 degrees Longitude, which designates the baseline for Global Standard Time, and Maupiti is +10 hours.  There is a three hour difference thus Maupiti is -3 hours Standard Time behind Grand Junction.  Remember the sun travels west and any time zone measured west of a location is considered - hours or earlier while time zones measured going east would be + hours or later.

If however we count the hour difference going east, Maupiti would be 24 - 3 or +21 hours ahead of Grand Junction (Note - there are 24 time zones in the world).

Why are both of these calculations wrong while we were in Maupiti?  Because they each are based on both locations adhering to Standard Time and during many months, including August and September, Colorado along with most of the US observes Daylight Savings Time which actually creates an Adjusted Standard Time for Grand Junction of +6 hours.  The actual time difference then makes Maupiti -4 hours behind Grand Junction, when properly counting going west.

Now on to the International Date Line and our current location Tonga.  The International Date Line is in the middle of the 12th Standard Time zone at 180 degrees Longitude, which can be either +12 or -12 hours depending on which side of the Date Line the location is located.  Per Standard Time Zone definitions the Tonga Islands would be considered to be +11 hours, on the same side of the Date Line and day as Grand Junction.  

However there was a competition between island groups in the South Pacific to make the claim for being the first place on earth to officially change days. Tonga changed its Standard Time Zone definition from +11 hours to -13 hours, thereby moving the Date Line to the east of the island group.  

When we arrived in Tonga today we needed to adjust our clocks one hour earlier and because we passed Tonga’s adjusted International Date Line we also had to move a day ahead, meaning today is Friday September 15th and because of the date change we count time zone hours to the east and are now +20 hours ahead of Grand Junction, not -5 hours behind.

Confused Yet?  Here is a diagram that may help.  Note that Tonga lost the battle to be the first nation to change days as Kiribati officially changed its Standard Time Zone definition to -14 hours moving the Date Line an hour earlier than Tonga to the east of the Kiribati island group.