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.

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 International Date Line	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	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 International Date Line	UTC+12

Selected table of times and dates

GMT	Lae UTC+10	Itasca UTC-11.5	PST UTC-8	EST UTC-5
29-6 0500 GMT	29-6 1500 Lae	28-6 1730 Ita	28-6 2100 PST	29-6 0000 EST
29-6 0600 GMT	29-6 1600 Lae	28-6 1830 Ita	28-6 2200 PST	29-6 0100 EST
29-6 0700 GMT	29-6 1700 Lae	28-6 1930 Ita	28-6 2300 PST	29-6 0200 EST
29-6 0800 GMT	29-6 1800 Lae	28-6 2030 Ita	29-6 0000 PST	29-6 0300 EST
29-6 0900 GMT	29-6 1900 Lae	28-6 2130 Ita	29-6 0100 PST	29-6 0400 EST
29-6 1000 GMT	29-6 2000 Lae	28-6 2230 Ita	29-6 0200 PST	29-6 0500 EST
29-6 1100 GMT	29-6 2100 Lae	28-6 2330 Ita	29-6 0300 PST	29-6 0600 EST
29-6 1200 GMT	29-6 2200 Lae	29-6 0030 Ita	29-6 0400 PST	29-6 0700 EST
29-6 1300 GMT	29-6 2300 Lae	29-6 0130 Ita	29-6 0500 PST	29-6 0800 EST
29-6 1400 GMT	30-6 0000 Lae	29-6 0230 Ita	29-6 0600 PST	29-6 0900 EST
29-6 1500 GMT	30-6 0100 Lae	29-6 0330 Ita	29-6 0700 PST	29-6 1000 EST
29-6 1600 GMT	30-6 0200 Lae	29-6 0430 Ita	29-6 0800 PST	29-6 1100 EST
29-6 1700 GMT	30-6 0300 Lae	29-6 0530 Ita	29-6 0900 PST	29-6 1200 EST
29-6 1800 GMT	30-6 0400 Lae	29-6 0630 Ita	29-6 1000 PST	29-6 1300 EST
29-6 1900 GMT	30-6 0500 Lae	29-6 0730 Ita	29-6 1100 PST	29-6 1400 EST
29-6 2000 GMT	30-6 0600 Lae	29-6 0830 Ita	29-6 1200 PST	29-6 1500 EST
29-6 2100 GMT	30-6 0700 Lae	29-6 0930 Ita	29-6 1300 PST	29-6 1600 EST
29-6 2200 GMT	30-6 0800 Lae	29-6 1030 Ita	29-6 1400 PST	29-6 1700 EST
29-6 2300 GMT	30-6 0900 Lae	29-6 1130 Ita	29-6 1500 PST	29-6 1800 EST
30-6 0000 GMT	30-6 1000 Lae	29-6 1230 Ita	29-6 1600 PST	29-6 1900 EST
30-6 0100 GMT	30-6 1100 Lae	29-6 1330 Ita	29-6 1700 PST	29-6 2000 EST
30-6 0200 GMT	30-6 1200 Lae	29-6 1430 Ita	29-6 1800 PST	29-6 2100 EST
30-6 0300 GMT	30-6 1300 Lae	29-6 1530 Ita	29-6 1900 PST	29-6 2200 EST
30-6 0400 GMT	30-6 1400 Lae	29-6 1630 Ita	29-6 2000 PST	29-6 2300 EST
30-6 0500 GMT	30-6 1500 Lae	29-6 1730 Ita	29-6 2100 PST	30-6 0000 EST
30-6 0600 GMT	30-6 1600 Lae	29-6 1830 Ita	29-6 2200 PST	30-6 0100 EST
30-6 0700 GMT	30-6 1700 Lae	29-6 1930 Ita	29-6 2300 PST	30-6 0200 EST
30-6 0800 GMT	30-6 1800 Lae	29-6 2030 Ita	30-6 0000 PST	30-6 0300 EST
30-6 0900 GMT	30-6 1900 Lae	29-6 2130 Ita	30-6 0100 PST	30-6 0400 EST
30-6 1000 GMT	30-6 2000 Lae	29-6 2230 Ita	30-6 0200 PST	30-6 0500 EST
30-6 1100 GMT	30-6 2100 Lae	29-6 2330 Ita	30-6 0300 PST	30-6 0600 EST
30-6 1200 GMT	30-6 2200 Lae	30-6 0030 Ita	30-6 0400 PST	30-6 0700 EST
30-6 1300 GMT	30-6 2300 Lae	30-6 0130 Ita	30-6 0500 PST	30-6 0800 EST
30-6 1400 GMT	1-7 0000 Lae	30-6 0230 Ita	30-6 0600 PST	30-6 0900 EST
30-6 1500 GMT	1-7 0100 Lae	30-6 0330 Ita	30-6 0700 PST	30-6 1000 EST
30-6 1600 GMT	1-7 0200 Lae	30-6 0430 Ita	30-6 0800 PST	30-6 1100 EST
30-6 1700 GMT	1-7 0300 Lae	30-6 0530 Ita	30-6 0900 PST	30-6 1200 EST
30-6 1800 GMT	1-7 0400 Lae	30-6 0630 Ita	30-6 1000 PST	30-6 1300 EST
30-6 1900 GMT	1-7 0500 Lae	30-6 0730 Ita	30-6 1100 PST	30-6 1400 EST
30-6 2000 GMT	1-7 0600 Lae	30-6 0830 Ita	30-6 1200 PST	30-6 1500 EST
30-6 2100 GMT	1-7 0700 Lae	30-6 0930 Ita	30-6 1300 PST	30-6 1600 EST
30-6 2200 GMT	1-7 0800 Lae	30-6 1030 Ita	30-6 1400 PST	30-6 1700 EST
30-6 2300 GMT	1-7 0900 Lae	30-6 1130 Ita	30-6 1500 PST	30-6 1800 EST
1-7 0000 GMT	1-7 1000 Lae	30-6 1230 Ita	30-6 1600 PST	30-6 1900 EST
1-7 0100 GMT	1-7 1100 Lae	30-6 1330 Ita	30-6 1700 PST	30-6 2000 EST
1-7 0200 GMT	1-7 1200 Lae	30-6 1430 Ita	30-6 1800 PST	30-6 2100 EST
1-7 0300 GMT	1-7 1300 Lae	30-6 1530 Ita	30-6 1900 PST	30-6 2200 EST
1-7 0400 GMT	1-7 1400 Lae	30-6 1630 Ita	30-6 2000 PST	30-6 2300 EST
1-7 0500 GMT	1-7 1500 Lae	30-6 1730 Ita	30-6 2100 PST	1-7 0000 EST
1-7 0600 GMT	1-7 1600 Lae	30-6 1830 Ita	30-6 2200 PST	1-7 0100 EST
1-7 0700 GMT	1-7 1700 Lae	30-6 1930 Ita	30-6 2300 PST	1-7 0200 EST
1-7 0800 GMT	1-7 1800 Lae	30-6 2030 Ita	1-7 0000 PST	1-7 0300 EST
1-7 0900 GMT	1-7 1900 Lae	30-6 2130 Ita	1-7 0100 PST	1-7 0400 EST
1-7 1000 GMT	1-7 2000 Lae	30-6 2230 Ita	1-7 0200 PST	1-7 0500 EST
1-7 1100 GMT	1-7 2100 Lae	30-6 2330 Ita	1-7 0300 PST	1-7 0600 EST
1-7 1200 GMT	1-7 2200 Lae	1-7 0030 Ita	1-7 0400 PST	1-7 0700 EST
1-7 1300 GMT	1-7 2300 Lae	1-7 0130 Ita	1-7 0500 PST	1-7 0800 EST
1-7 1400 GMT	2-7 0000 Lae	1-7 0230 Ita	1-7 0600 PST	1-7 0900 EST
1-7 1500 GMT	2-7 0100 Lae	1-7 0330 Ita	1-7 0700 PST	1-7 1000 EST
1-7 1600 GMT	2-7 0200 Lae	1-7 0430 Ita	1-7 0800 PST	1-7 1100 EST
1-7 1700 GMT	2-7 0300 Lae	1-7 0530 Ita	1-7 0900 PST	1-7 1200 EST
1-7 1800 GMT	2-7 0400 Lae	1-7 0630 Ita	1-7 1000 PST	1-7 1300 EST
1-7 1900 GMT	2-7 0500 Lae	1-7 0730 Ita	1-7 1100 PST	1-7 1400 EST
1-7 2000 GMT	2-7 0600 Lae	1-7 0830 Ita	1-7 1200 PST	1-7 1500 EST
1-7 2100 GMT	2-7 0700 Lae	1-7 0930 Ita	1-7 1300 PST	1-7 1600 EST
1-7 2200 GMT	2-7 0800 Lae	1-7 1030 Ita	1-7 1400 PST	1-7 1700 EST
1-7 2300 GMT	2-7 0900 Lae	1-7 1130 Ita	1-7 1500 PST	1-7 1800 EST
2-7 0000 GMT	2-7 1000 Lae	1-7 1230 Ita	1-7 1600 PST	1-7 1900 EST
2-7 0100 GMT	2-7 1100 Lae	1-7 1330 Ita	1-7 1700 PST	1-7 2000 EST
2-7 0200 GMT	2-7 1200 Lae	1-7 1430 Ita	1-7 1800 PST	1-7 2100 EST
2-7 0300 GMT	2-7 1300 Lae	1-7 1530 Ita	1-7 1900 PST	1-7 2200 EST
2-7 0400 GMT	2-7 1400 Lae	1-7 1630 Ita	1-7 2000 PST	1-7 2300 EST
2-7 0500 GMT	2-7 1500 Lae	1-7 1730 Ita	1-7 2100 PST	2-7 0000 EST
2-7 0600 GMT	2-7 1600 Lae	1-7 1830 Ita	1-7 2200 PST	2-7 0100 EST
2-7 0700 GMT	2-7 1700 Lae	1-7 1930 Ita	1-7 2300 PST	2-7 0200 EST
2-7 0800 GMT	2-7 1800 Lae	1-7 2030 Ita	2-7 0000 PST	2-7 0300 EST
2-7 0900 GMT	2-7 1900 Lae	1-7 2130 Ita	2-7 0100 PST	2-7 0400 EST
2-7 1000 GMT	2-7 2000 Lae	1-7 2230 Ita	2-7 0200 PST	2-7 0500 EST
2-7 1100 GMT	2-7 2100 Lae	1-7 2330 Ita	2-7 0300 PST	2-7 0600 EST
2-7 1200 GMT	2-7 2200 Lae	2-7 0030 Ita	2-7 0400 PST	2-7 0700 EST
2-7 1300 GMT	2-7 2300 Lae	2-7 0130 Ita	2-7 0500 PST	2-7 0800 EST
2-7 1400 GMT	3-7 0000 Lae	2-7 0230 Ita	2-7 0600 PST	2-7 0900 EST
2-7 1500 GMT	3-7 0100 Lae	2-7 0330 Ita	2-7 0700 PST	2-7 1000 EST
2-7 1600 GMT	3-7 0200 Lae	2-7 0430 Ita	2-7 0800 PST	2-7 1100 EST
2-7 1700 GMT	3-7 0300 Lae	2-7 0530 Ita	2-7 0900 PST	2-7 1200 EST
2-7 1800 GMT	3-7 0400 Lae	2-7 0630 Ita	2-7 1000 PST	2-7 1300 EST
2-7 1900 GMT	3-7 0500 Lae	2-7 0730 Ita	2-7 1100 PST	2-7 1400 EST
2-7 2000 GMT	3-7 0600 Lae	2-7 0830 Ita	2-7 1200 PST	2-7 1500 EST
2-7 2100 GMT	3-7 0700 Lae	2-7 0930 Ita	2-7 1300 PST	2-7 1600 EST
2-7 2200 GMT	3-7 0800 Lae	2-7 1030 Ita	2-7 1400 PST	2-7 1700 EST
2-7 2300 GMT	3-7 0900 Lae	2-7 1130 Ita	2-7 1500 PST	2-7 1800 EST
3-7 0000 GMT	3-7 1000 Lae	2-7 1230 Ita	2-7 1600 PST	2-7 1900 EST
3-7 0100 GMT	3-7 1100 Lae	2-7 1330 Ita	2-7 1700 PST	2-7 2000 EST
3-7 0200 GMT	3-7 1200 Lae	2-7 1430 Ita	2-7 1800 PST	2-7 2100 EST
3-7 0300 GMT	3-7 1300 Lae	2-7 1530 Ita	2-7 1900 PST	2-7 2200 EST

Ric's Cheatsheet

-12	-11.5	-11	-10.5	-8	-7	-6	-5	Greenwich	+9	+10	+11	+12
Date Line	Itasca	Baker	Honolulu	Oakland	Denver	Chicago	NYC	UTC	Darwin	Lae	Wake	Tarawa
			Howland	PST	MST	CST	EST
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

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