Time and longitude
One of the by-products of modern technology is that international events from around the
world are reported on television as they are happening. These invents compete with local
or national news or other programming for our attention. Whether it is a sports event, a
natural disaster or any other major event, it is promptly reported on some television
channel and beamed around the world. Hearing about events that are already happening
tomorrow can be confusing. Keeping track of what day and time it is where these events
occur can be essential to an understanding of the event. It is, therefore, important to
understand world time zones, the role of the International Date Line and how these
concepts relate to location (the longitude of a place).
Procedure:
Use the approximate longitude for each city listed below, a world map or globe and the
time and longitude computer to answer the following questions:
City
London
New York
Los Angeles
Calcutta
Shanghai
Osaka
Actual
0°07’W
73°58’W
118°14’W
88°22’E
121°27’E
135°27’E
Approximate
0°
75°W
120°W
90°E
120°E
135°E
1. How many degrees difference in longitude are there between the following cities? (Be
sure to note the direction of travel)
Starting at:
Los Angeles
London
New York
Direction of Travel
Eastward
Westward
__________
__________
__________
__________
__________
__________
Ending at:
Shanghai
Osaka
Calcutta
2. How many hours difference are there between the following cities? (Again, note the
direction of travel)
Starting at:
Los Angeles
London
New York
Direction of Travel
Eastward
Westward
_______hrs
_______hrs
_______hrs
_______hrs
_______hrs
_______hrs
Ending at:
Shanghai
Osaka
Calcutta
The Prime Meridian is an imaginary north-south line of longitude that extends from pole
to pole through the Royal Observatory in Greenwich, a suburb of southeastern London.
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Distances are measured from zero to 180° west of the Prime Meridian and from zero to
180° east. Opposite the Prime Meridian on the globe is the International Date Line,
where the date changes, and where each new day begins. The International Date Line
follows the 180° meridian for much of its length, with some deviations for political units.
Use the Time and Longitude Computer for the following questions. To use the Time and
Longitude Computer, attach the smaller, longitude dial to the larger, time dial using a
brass tab (be sure to align the crosses in the center of the two dials). Then spin the inner
dial so that a desired longitude aligns with a given time on the outer dial (ideally, the
longitude lines and the lines on the time dial should match up exactly – move the inner
dial slightly so that they do). Now (without moving the dials) read the time at any other
longitude value (your answer will always be a whole hour). Note that there are two (2)
locations on the Time and Longitude Computer where the day of the week changes –
Midnight and at the International Date Line. When moving clockwise across midnight,
the day always goes back (For Example: You move from 1:00 AM on Saturday to 11:00
PM on Friday). Conversely, when moving counter-clockwise across midnight, the day
always goes forward. Arrows on the longitude dial tell you whether to advance or go
back a day when crossing the International Date Line. At MOST, there can be only TWO
DAYS on the Earth at any given time – NEVER any more than that. Every day there is
one instant in which there is only ONE day on the Earth.
3. If it is 12:00 noon on Monday in Los Angeles (120°W):
What is the time of day in Osaka (135°E)?
What is the day of the week in Osaka (135°E)?
What is the longitude of midnight?
Monday covers how many degrees of longitude?
Tuesday covers how many degrees of longitude?
__________
__________
__________
__________
__________
4. If it is 8:00 AM on Saturday in Shanghai (120°E):
What is the time of day in Los Angeles (120°W)?
What is the day of the week in Los Angeles (120°W)?
What is the longitude of midnight?
Friday covers how many degrees of longitude?
Saturday covers how many degrees of longitude?
__________
__________
__________
__________
__________
__________
5. If it is 6:00 PM on Thursday in Calcutta (90°E):
What is the time of day in Los Angeles (120°W)?
What is the day of the week in Los Angeles (120°)?
What is the longitude of midnight?
Thursday covers how many degrees of longitude?
Wednesday covers how many degrees of longitude?
__________
__________
__________
__________
__________
Do not use the Time and Longitude Computer for the following questions.
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6. If two places are separated by 0° of latitude and 90° of longitude, how many hours of
time separate these two places?
7. If two places are separated by 45° of latitude and 0° of longitude, how many hours of
time separate these two places?
8. If each hour to time is equal to 15° of longitude, what portion of a degree of longitude
is equal to one (1) second of time?
9. At the equator, how far (in miles) does one travel in five (5) minutes of time, due to
the rotation of the Earth? (Hint: Look for the circumference of the Earth in your text or
lecture notes).
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