# Timezones

## 1937 Time Zones

The basic information for this table is found in Randy Jacobson's work, "Time Zones for Earhart Radio Message Database."

From local to GMT
To determine how to get back to GMT time from a local time, always add the offsets given below to get GMT time.
From GMT to local
Subtract the value of the offset from GMT to get the local time.
Math reminders
• When we add negative numbers, the result is the same as subtracting the absolute value of the number from the base.
0000 GMT + (-1) = 0000 - 0100 = 2300
• When we subtract negative numbers, the result is the same as adding the absolute value of the number to the base.
0000 GMT - (-1) = 0000 + 0100 = 0100
Dateline
If your calculation is crossing the dateline, add a day if transiting east to west; subtract a day if the your calculation is transiting west to east.
In the case of their last flight, Earhart and Noonan took off at 1000 hours on 2 July in Lae, which was 0000 GMT on 2 July in Greenwich. After flying for 14 hours from west to east, the aircraft would pass the midnight hour from July 2 to July 3 with respect to Lae, but when it crossed the dateline, it would then be "back" on July 2nd.
Time Zone Conventions

The convention used in this table for Time Zone values is the opposite of the current UTC convention. Jacobson followed the convention used by navigators and the Navy. Time zones are positive because "they are interested in finding GMT, also known as GCT, UTC and Z (Zulu time), starting from the local time shown on the onboard clocks." In this convention, add the offset to the local time to derive Zulu (UTC) time.[1]

To convert to the UTC convention, change all of the positive offsets to negative numbers and all of the negative offsets to positive numbers.

Ship/Place Time of TZ Change Time Zone offset from GMT
Baker 11
Honolulu 10.5
Howland 10.5
Jarvis 10.5
Lae (-10)
San Francisco 8
Washington, DC 5
London (-1)
American Samoa 11
CINCUS 8
COMINBATFOR 10.5
COMDESCOFOR 8
COMAIRBASEFOR 8
COMBATSHIPS 8
COMAIRBATFOR 8
Duane 13 Jan 1937 10.5
15 Jan 0530 11
24 Jan 1300 10.5
Shoshone March 10, 0700 10.5

(stays 10.5 for duration of first attempt)

Itasca 19 June 0000 10.5
20 June 1400 11
22 June 1400 11.5
12 July 1400 12
14 July 0000 11.5
20 July 1400 11
23 July 0800 10.5
Ontario 17 June 1937 0700 11
18 June 0000 12
20 June 1100 (-12)
22 June 1800 (-11)
5 July 0800 -12
7 July 1500 12
9 July 1500 11
Swan 1 July 0000 11
6 July 1300 11.5
10 July 0300 11
10 July 1700 11.5
12 July 1900 12
15 July 0000 (-12)
Colorado 3 July 1400 10.5
4 July 4 1300 11
7 July 1300 11.5
14 July 1300 10.5

Lexington
Drayton
Cushing
Lamson

1 July 1937 8
5 July 1600 9
7 July 1600 10
8 July 1030: 10.5
12 July 11.5
21 July 10.5

## International Date Line

Wikipedia, "International Date Line":
The International Date Line (IDL) is an imaginary line on the surface of the Earth, running between the north and south poles, that demarcates one calendar day from the next. It passes through the middle of the Pacific Ocean, roughly along the 180° longitude, opposite the Prime Meridian, but it is drawn with diversions to pass around some territories and island groups.
In conjunction with the moving imaginary line opposite the sun corresponding to midnight, the IDL separates the two calendar days being used somewhere on earth most of the time, 22 hours out of each 24. Three different calendar days are in simultaneous use during a two-hour period between 10:00 and 11:59 (UTC) each day, due to the use of additional date-shifted time zones in a few areas affected by substantial deviations of the date line from the 180th meridian. The use of these additional time zones also precludes the possibility of the entire planet observing only a single date at the instant when midnight crosses the IDL.
In the absence of a simultaneous time zone change, a traveler crossing the IDL eastbound subtracts one day, or 24 hours, so that the the calendar date to the west of the line is repeated. Crossing the IDL westbound results in 24 hours being added, advancing the calendar date by one day. The line is necessary in order to have a fixed, albeit arbitrary, boundary on the globe where the calendar date advances in the westbound direction.

### Meditation on the Date Line

• A day represents one rotation of the earth around its own axis.
• There are only 24 hours in a day.
• Each hour on the clock represents a "time zone" covered on the face of the earth by the apparent movement of the sun over that region or by the logical "movement" of a timeline circling the earth at the rate of 24 hours per day. One hour of time = one time zone on the map.
• The apparent motion of the sun around the earth is from east to west. Comparing any two time zones that are side-by-side, the eastern time zone will be ahead of the western time zone by one hour. The eastern time zone gets the sun (or midnight) one hour before the time zone to the west of it.
• No matter where one chooses to begin the count of 24 hours and 24 time zones, the 24th time zone will always end up right next to the first time zone. In terms of the apparent motion of the sun or the logical "motion" of midnight, the 24th time zone is only one hour ahead of the first time zone on the clock, but it is 24 hours behind the first time zone on the calendar.
• The International Date Line divides the UTC+12 (or UTC-12) time zone into two parts. On the western side of the line (UTC+12), it is one full calendar day (24 hours) ahead of the eastern side of the line (UTC-12).
• The time of day is the same, but the date is different. People who cross the line from west to east do not have to change their clocks; they do have to change the day's date,
For example:
3 July 0000 UTC+12, west of the dateline = 2 July 0000 UTC-12, east of the dateline

## 24 hours, 25 time zones

The UTC convention actually has 25 time. Twelve are west of Greenwich (UTC ± 0), UTC-1 .. UTC -12. Twelve are east of Greenwich, UTC+1 .. UTC+12.

12 west + 12 east + 1 at 0 = 25 time zones.

UTC-12 gives the same time of day as UTC+12. If it is 0000 UTC, then it is 1200 (noon) at UTC-12 and 1200 (noon) at UTC+12. As noted above, that time zone is divided by the date line, so that even though it is the same time of day at UTC-12 and UTC+12, it is a different day of the week and a different date on the calendar. UTC+12 is exactly one full day ahead of UTC-12.

To get the UTC time from a local time zone, subtract the offset from the local time.

• Monday 2020 EST - (-5) = 0120 Tuesday UTC. I know it is the next day because my calculation took me past midnight. Tuesday arrives in the Zulu time zone before it gets here five hours later.
• Monday 0920 Lae - 10 = Sunday 2320 UTC on the previous day. I know it is the day before because I had to cross midnight heading in the other direction from my first example. Monday arrives in Lae 10 hours before it reaches the Zulu time zone.

To get to a local time zone from UTC, add the offset from the UTC time.

• Wednesday 1400 UTC + (-5) = Wednesday 0900 EST
• Wednesday 1400 UTC + 10 = Thursday 0000 Lae.
Name Includes Offset
M/Y UTC-12
X-ray UTC-11
Whiskey UTC-10
Victor UTC-9
Uniform

PST--Pacific Standard Time

• Seattle
• San Francisco
• Los Angeles
• Oakland
UTC-8
Tango

MST--Mountain Standard Time

• Phoenix
• Salt Lake City
• Denver
UTC-7
Sierra

CST--Central Standard Time

• Chicago
• Houston
• New Orleans
UTC-6
Romeo

EST--Eastern Standard Time

• Detroit
• New York
• Miami
• D.C.
UTC-5
Quebec UTC-4
Papa UTC-3
Oscar UTC-2
November UTC-1
Zulu
• Greenwich
• GCT--Greenwich Common Time
• GMT--Greenwich Mean Time
• UTC--Coordinated Universal Time[2]
UTC±00
Alpha UTC+1
Bravo UTC+2
Charlie UTC+3
Delta UTC+4
Echo UTC+5
Foxtrot UTC+6
Golf UTC+7
Hotel UTC+8
India
• Tokyo, Japan
UTC+9
Kilo

Port Moresby, Papua New Guinea

• Lae, New Guinea
UTC+10
Lima UTC+11
M/Y UTC+12

## Selected table of times and dates

GMT Lae UTC+10 Itasca UTC-11.5 PST UTC-8 EST UTC-5
06-29 0500 GMT 06-29 1500 Lae 06-28 1730 Ita 06-28 2100 PST 06-29 0000 EST
06-29 0600 GMT 06-29 1600 Lae 06-28 1830 Ita 06-28 2200 PST 06-29 0100 EST
06-29 0700 GMT 06-29 1700 Lae 06-28 1930 Ita 06-28 2300 PST 06-29 0200 EST
06-29 0800 GMT 06-29 1800 Lae 06-28 2030 Ita 06-29 0000 PST 06-29 0300 EST
06-29 0900 GMT 06-29 1900 Lae 06-28 2130 Ita 06-29 0100 PST 06-29 0400 EST
06-29 1000 GMT 06-29 2000 Lae 06-28 2230 Ita 06-29 0200 PST 06-29 0500 EST
06-29 1100 GMT 06-29 2100 Lae 06-28 2330 Ita 06-29 0300 PST 06-29 0600 EST
06-29 1200 GMT 06-29 2200 Lae 06-29 0030 Ita 06-29 0400 PST 06-29 0700 EST
06-29 1300 GMT 06-29 2300 Lae 06-29 0130 Ita 06-29 0500 PST 06-29 0800 EST
06-29 1400 GMT 06-30 0000 Lae 06-29 0230 Ita 06-29 0600 PST 06-29 0900 EST
06-29 1500 GMT 06-30 0100 Lae 06-29 0330 Ita 06-29 0700 PST 06-29 1000 EST
06-29 1600 GMT 06-30 0200 Lae 06-29 0430 Ita 06-29 0800 PST 06-29 1100 EST
06-29 1700 GMT 06-30 0300 Lae 06-29 0530 Ita 06-29 0900 PST 06-29 1200 EST
06-29 1800 GMT 06-30 0400 Lae 06-29 0630 Ita 06-29 1000 PST 06-29 1300 EST
06-29 1900 GMT 06-30 0500 Lae 06-29 0730 Ita 06-29 1100 PST 06-29 1400 EST
06-29 2000 GMT 06-30 0600 Lae 06-29 0830 Ita 06-29 1200 PST 06-29 1500 EST
06-29 2100 GMT 06-30 0700 Lae 06-29 0930 Ita 06-29 1300 PST 06-29 1600 EST
06-29 2200 GMT 06-30 0800 Lae 06-29 1030 Ita 06-29 1400 PST 06-29 1700 EST
06-29 2300 GMT 06-30 0900 Lae 06-29 1130 Ita 06-29 1500 PST 06-29 1800 EST
06-30 0000 GMT 06-30 1000 Lae 06-29 1230 Ita 06-29 1600 PST 06-29 1900 EST
06-30 0100 GMT 06-30 1100 Lae 06-29 1330 Ita 06-29 1700 PST 06-29 2000 EST
06-30 0200 GMT 06-30 1200 Lae 06-29 1430 Ita 06-29 1800 PST 06-29 2100 EST
06-30 0300 GMT 06-30 1300 Lae 06-29 1530 Ita 06-29 1900 PST 06-29 2200 EST
06-30 0400 GMT 06-30 1400 Lae 06-29 1630 Ita 06-29 2000 PST 06-29 2300 EST
06-30 0500 GMT 06-30 1500 Lae 06-29 1730 Ita 06-29 2100 PST 06-30 0000 EST
06-30 0600 GMT 06-30 1600 Lae 06-29 1830 Ita 06-29 2200 PST 06-30 0100 EST
06-30 0700 GMT 06-30 1700 Lae 06-29 1930 Ita 06-29 2300 PST 06-30 0200 EST
06-30 0800 GMT 06-30 1800 Lae 06-29 2030 Ita 06-30 0000 PST 06-30 0300 EST
06-30 0900 GMT 06-30 1900 Lae 06-29 2130 Ita 06-30 0100 PST 06-30 0400 EST
06-30 1000 GMT 06-30 2000 Lae 06-29 2230 Ita 06-30 0200 PST 06-30 0500 EST
06-30 1100 GMT 06-30 2100 Lae 06-29 2330 Ita 06-30 0300 PST 06-30 0600 EST
06-30 1200 GMT 06-30 2200 Lae 06-30 0030 Ita 06-30 0400 PST 06-30 0700 EST
06-30 1300 GMT 06-30 2300 Lae 06-30 0130 Ita 06-30 0500 PST 06-30 0800 EST
06-30 1400 GMT 07-01 0000 Lae 06-30 0230 Ita 06-30 0600 PST 06-30 0900 EST
06-30 1500 GMT 07-01 0100 Lae 06-30 0330 Ita 06-30 0700 PST 06-30 1000 EST
06-30 1600 GMT 07-01 0200 Lae 06-30 0430 Ita 06-30 0800 PST 06-30 1100 EST
06-30 1700 GMT 07-01 0300 Lae 06-30 0530 Ita 06-30 0900 PST 06-30 1200 EST
06-30 1800 GMT 07-01 0400 Lae 06-30 0630 Ita 06-30 1000 PST 06-30 1300 EST
06-30 1900 GMT 07-01 0500 Lae 06-30 0730 Ita 06-30 1100 PST 06-30 1400 EST
06-30 2000 GMT 07-01 0600 Lae 06-30 0830 Ita 06-30 1200 PST 06-30 1500 EST
06-30 2100 GMT 07-01 0700 Lae 06-30 0930 Ita 06-30 1300 PST 06-30 1600 EST
06-30 2200 GMT 07-01 0800 Lae 06-30 1030 Ita 06-30 1400 PST 06-30 1700 EST
06-30 2300 GMT 07-01 0900 Lae 06-30 1130 Ita 06-30 1500 PST 06-30 1800 EST
07-01 0000 GMT 07-01 1000 Lae 06-30 1230 Ita 06-30 1600 PST 06-30 1900 EST
07-01 0100 GMT 07-01 1100 Lae 06-30 1330 Ita 06-30 1700 PST 06-30 2000 EST
07-01 0200 GMT 07-01 1200 Lae 06-30 1430 Ita 06-30 1800 PST 06-30 2100 EST
07-01 0300 GMT 07-01 1300 Lae 06-30 1530 Ita 06-30 1900 PST 06-30 2200 EST
07-01 0400 GMT 07-01 1400 Lae 06-30 1630 Ita 06-30 2000 PST 06-30 2300 EST
07-01 0500 GMT 07-01 1500 Lae 06-30 1730 Ita 06-30 2100 PST 07-01 0000 EST
07-01 0600 GMT 07-01 1600 Lae 06-30 1830 Ita 06-30 2200 PST 07-01 0100 EST
07-01 0700 GMT 07-01 1700 Lae 06-30 1930 Ita 06-30 2300 PST 07-01 0200 EST
07-01 0800 GMT 07-01 1800 Lae 06-30 2030 Ita 07-01 0000 PST 07-01 0300 EST
07-01 0900 GMT 07-01 1900 Lae 06-30 2130 Ita 07-01 0100 PST 07-01 0400 EST
07-01 1000 GMT 07-01 2000 Lae 06-30 2230 Ita 07-01 0200 PST 07-01 0500 EST
07-01 1100 GMT 07-01 2100 Lae 06-30 2330 Ita 07-01 0300 PST 07-01 0600 EST
07-01 1200 GMT 07-01 2200 Lae 07-01 0030 Ita 07-01 0400 PST 07-01 0700 EST
07-01 1300 GMT 07-01 2300 Lae 07-01 0130 Ita 07-01 0500 PST 07-01 0800 EST
07-01 1400 GMT 07-02 0000 Lae 07-01 0230 Ita 07-01 0600 PST 07-01 0900 EST
07-01 1500 GMT 07-02 0100 Lae 07-01 0330 Ita 07-01 0700 PST 07-01 1000 EST
07-01 1600 GMT 07-02 0200 Lae 07-01 0430 Ita 07-01 0800 PST 07-01 1100 EST
07-01 1700 GMT 07-02 0300 Lae 07-01 0530 Ita 07-01 0900 PST 07-01 1200 EST
07-01 1800 GMT 07-02 0400 Lae 07-01 0630 Ita 07-01 1000 PST 07-01 1300 EST
07-01 1900 GMT 07-02 0500 Lae 07-01 0730 Ita 07-01 1100 PST 07-01 1400 EST
07-01 2000 GMT 07-02 0600 Lae 07-01 0830 Ita 07-01 1200 PST 07-01 1500 EST
07-01 2100 GMT 07-02 0700 Lae 07-01 0930 Ita 07-01 1300 PST 07-01 1600 EST
07-01 2200 GMT 07-02 0800 Lae 07-01 1030 Ita 07-01 1400 PST 07-01 1700 EST
07-01 2300 GMT 07-02 0900 Lae 07-01 1130 Ita 07-01 1500 PST 07-01 1800 EST
07-02 0000 GMT 07-02 1000 Lae 07-01 1230 Ita 07-01 1600 PST 07-01 1900 EST
07-02 0100 GMT 07-02 1100 Lae 07-01 1330 Ita 07-01 1700 PST 07-01 2000 EST
07-02 0200 GMT 07-02 1200 Lae 07-01 1430 Ita 07-01 1800 PST 07-01 2100 EST
07-02 0300 GMT 07-02 1300 Lae 07-01 1530 Ita 07-01 1900 PST 07-01 2200 EST
07-02 0400 GMT 07-02 1400 Lae 07-01 1630 Ita 07-01 2000 PST 07-01 2300 EST
07-02 0500 GMT 07-02 1500 Lae 07-01 1730 Ita 07-01 2100 PST 07-02 0000 EST
07-02 0600 GMT 07-02 1600 Lae 07-01 1830 Ita 07-01 2200 PST 07-02 0100 EST
07-02 0700 GMT 07-02 1700 Lae 07-01 1930 Ita 07-01 2300 PST 07-02 0200 EST
07-02 0800 GMT 07-02 1800 Lae 07-01 2030 Ita 07-02 0000 PST 07-02 0300 EST
07-02 0900 GMT 07-02 1900 Lae 07-01 2130 Ita 07-02 0100 PST 07-02 0400 EST
07-02 1000 GMT 07-02 2000 Lae 07-01 2230 Ita 07-02 0200 PST 07-02 0500 EST
07-02 1100 GMT 07-02 2100 Lae 07-01 2330 Ita 07-02 0300 PST 07-02 0600 EST
07-02 1200 GMT 07-02 2200 Lae 07-02 0030 Ita 07-02 0400 PST 07-02 0700 EST
07-02 1300 GMT 07-02 2300 Lae 07-02 0130 Ita 07-02 0500 PST 07-02 0800 EST
07-02 1400 GMT 07-03 0000 Lae 07-02 0230 Ita 07-02 0600 PST 07-02 0900 EST
07-02 1500 GMT 07-03 0100 Lae 07-02 0330 Ita 07-02 0700 PST 07-02 1000 EST
07-02 1600 GMT 07-03 0200 Lae 07-02 0430 Ita 07-02 0800 PST 07-02 1100 EST
07-02 1700 GMT 07-03 0300 Lae 07-02 0530 Ita 07-02 0900 PST 07-02 1200 EST
07-02 1800 GMT 07-03 0400 Lae 07-02 0630 Ita 07-02 1000 PST 07-02 1300 EST
07-02 1900 GMT 07-03 0500 Lae 07-02 0730 Ita 07-02 1100 PST 07-02 1400 EST
07-02 2000 GMT 07-03 0600 Lae 07-02 0830 Ita 07-02 1200 PST 07-02 1500 EST
07-02 2100 GMT 07-03 0700 Lae 07-02 0930 Ita 07-02 1300 PST 07-02 1600 EST
07-02 2200 GMT 07-03 0800 Lae 07-02 1030 Ita 07-02 1400 PST 07-02 1700 EST
07-02 2300 GMT 07-03 0900 Lae 07-02 1130 Ita 07-02 1500 PST 07-02 1800 EST
07-03 0000 GMT 07-03 1000 Lae 07-02 1230 Ita 07-02 1600 PST 07-02 1900 EST
07-03 0100 GMT 07-03 1100 Lae 07-02 1330 Ita 07-02 1700 PST 07-02 2000 EST
07-03 0200 GMT 07-03 1200 Lae 07-02 1430 Ita 07-02 1800 PST 07-02 2100 EST
07-03 0300 GMT 07-03 1300 Lae 07-02 1530 Ita 07-02 1900 PST 07-02 2200 EST

## Ric's Cheatsheet

-12 -11.5 -11 -10.5 -8 -7 -6 -5 ±0 +9 +10 +11 +12
Date Line Itasca Baker Honolulu Oakland Denver Chicago NYC Greenwich Darwin Lae Wake Tarawa
Howland PST MST CST EST UTC
12:00 12:30 13:00 13:30 16:00 17:00 18:00 19:00 00:00 09:00 10:00 11:00 12:00
13:00 13:30 14:00 14:30 17:00 18:00 19:00 20:00 01:00 10:00 11:00 12:00 13:00
14:00 14:30 15:00 15:30 18:00 19:00 20:00 21:00 02:00 11:00 12:00 13:00 14:00
15:00 15:30 16:00 16:30 19:00 20:00 21:00 22:00 03:00 12:00 13:00 14:00 15:00
16:00 16:30 17:00 17:30 20:00 21:00 22:00 23:00 04:00 13:00 14:00 15:00 16:00
17:00 17:30 18:00 18:30 21:00 22:00 23:00 00:00 05:00 14:00 15:00 16:00 17:00
18:00 18:30 19:00 19:30 22:00 23:00 00:00 01:00 06:00 15:00 16:00 17:00 18:00
19:00 19:30 20:00 20:30 23:00 00:00 01:00 02:00 07:00 16:00 17:00 18:00 19:00
20:00 20:30 21:00 21:30 00:00 01:00 02:00 03:00 08:00 17:00 18:00 19:00 20:00
21:00 21:30 22:00 22:30 01:00 02:00 03:00 04:00 09:00 18:00 19:00 20:00 21:00
22:00 22:30 23:00 23:30 02:00 03:00 04:00 05:00 10:00 19:00 20:00 21:00 22:00
23:00 23:30 00:00 00:30 03:00 04:00 05:00 06:00 11:00 20:00 21:00 22:00 23:00
00:00 00:30 01:00 01:30 04:00 05:00 06:00 07:00 12:00 21:00 22:00 23:00 00:00
01:00 01:30 02:00 02:30 05:00 06:00 07:00 08:00 13:00 22:00 23:00 00:00 01:00
02:00 02:30 03:00 03:30 06:00 07:00 08:00 09:00 14:00 23:00 00:00 01:00 02:00
03:00 03:30 04:00 04:30 07:00 08:00 09:00 10:00 15:00 00:00 01:00 02:00 03:00
04:00 04:30 05:00 05:30 08:00 09:00 10:00 11:00 16:00 01:00 02:00 03:00 04:00
05:00 05:30 06:00 06:30 09:00 10:00 11:00 12:00 17:00 02:00 03:00 04:00 05:00
06:00 06:30 07:00 07:30 10:00 11:00 12:00 13:00 18:00 03:00 04:00 05:00 06:00
07:00 07:30 08:00 08:30 11:00 12:00 13:00 14:00 19:00 04:00 05:00 06:00 07:00
08:00 08:30 09:00 09:30 12:00 13:00 14:00 15:00 20:00 05:00 06:00 07:00 08:00
09:00 09:30 10:00 10:30 13:00 14:00 15:00 16:00 21:00 06:00 07:00 08:00 09:00
10:00 10:30 11:00 11:30 14:00 15:00 16:00 17:00 22:00 07:00 08:00 09:00 10:00
11:00 11:30 12:00 12:30 15:00 16:00 17:00 18:00 23:00 08:00 09:00 10:00 11:00
12:00 12:30 13:00 13:30 16:00 17:00 18:00 19:00 00:00 09:00 10:00 11:00 12:00

## References

1. Gary LaPook, Forum.
2. "Coordinated Universal Time (UTC)." "UTC" is an arbitrary name created to avoid relying on any particular language for the acronym.