Time and Date Lab
Time is indefinite. It is defined as the interval between two events or
occurrences. For example, a lifetime – from birth to date, the growing season – from
the last killing frost of spring until the first killing frost of fall, and a year – time for the
Earth to travel from one point in its orbit around the sun and return.
Our time is based on the speed of the Earth’s rotation and the relationships of the
meridians to the sun. The Earth rotates 360 degrees in 24 hours, or 15 degrees in one
hour or one degree every four minutes.
Our ancestors used a sundial to tell time. It indicated time in relation to the
shadow of an arm as the sun moved across the sky. When the sun is over any
meridian, it is noon sun time on that meridian. The sun time of other meridians is found
by the distance in degrees between the meridian and the meridian under the sun,
divided by the speed of the Earth’s rotation. The Earth rotates at an average speed of
1020 miles per hour at the equator.
Try this example: if the sun is on the prime meridian (12 noon), what time is it in
York, PA (76 degrees west longitude)?
The distance between the two places is 76 degrees, divided by 15 degree/hour.
The speed of the Earth’s rotation is 5 hours with 1 degree as the remainder. One
degree multiplied by 4 minutes (4 minutes per degree) is 4 minutes. Thus, York’s sun
time is 5 hours and 4 minutes before noon or 6:56 A.M.
Please try the following:
1. If the vertical sun is directly over the meridian that passes through York, what sun
time would it be in London?
2. The time at Leningrad (30 degrees east longitude) is 5:00 P.M. sun time. What
sun time would it be at 60 degrees west longitude?
3. If it is 12 noon at 75 degrees west (Philadelphia), what sun time is it in York?
The time wheel is a device for telling time anywhere in the world. It is a
representation of the Earth (the center wheel), turning in relation to the vertical sun.
The center of the wheel would represent the North Pole and the circumference, the
equator. Notice the direction of the Earth’s rotation (W to E).
Orient the time wheel so that the prime meridian is at noon.
When it is noon at 0 degrees longitude, what is the time at the following
longitudes? 180 degrees (4); 90 degrees East (5); 90 degrees West (6)?
When it is midnight at 0 degrees longitude, what is the time at the following
longitudes? 180 degrees (7); 90 degrees East (8); 90 degrees West (9)?
Sun time worked fine for our early ancestors, but as travel became faster and life
more complex, a problem developed as every village had a different sun time.
American railroads, about 1870, introduced a standardized system covering
considerable belts of territory. This was further complicated by the railroads themselves
as each kept a different time. The obvious solution was a standard time, based on a
sun time of a central meridian, which would be given wide strips of country on both
sides. It is evident that if central meridians were placed 15 degrees apart, adjacent
zones would have standard times differing by exactly one hour.
The present system of standard time in the United States was placed in
operation in 1883, but it was not until 1918 that Congress passed legislation setting up
the boundaries between the time zones.
Eastern standard time
Central standard time
Mountain standard time
Pacific standard time
Alaska standard time
Hawaii standard time
75th meridian
90th meridian
105th meridian
120th meridian
150th meridian
150th meridian
Theoretically, the system would have resulted in belts exactly 7 ½ degrees east
and west of each central meridian. However, because of local zones of influence,
natural boundaries, or state lines, the lines are irregular. (See the time zone maps of
the world and the United States.)
In Clarion, PA (79 degrees West), our watches (standard time) are off 16 minutes
from the sun time. When it is 12 noon in Philadelphia (75 degrees West), what is the
sun time in Clarion (79 degrees West)? The differences between Clarion and
Philadelphia is 4 degrees and as the Earth takes 4 minutes to turn one degree, the time
difference is 16 minutes and it would be 11:44 A.M. when our watches show 12 noon
standard time.
Work the following:
10. If it is 12-noon sun time at Clarion (79 degrees West longitude), what time would
our watched show?
11. When it is 3:00 P.M. standard time in Honolulu (150 degrees West), what time
(standard) is it in Clarion?
12. The time is 2:00 P.M. standard time December 31, in York. What time is it in
Singapore (105 degrees East longitude)?
Few of us wonder where a given date first comes into or finally goes out of existence.
They all first appear and finally disappear at the International Date Line. Locate the
International Date Line on the globe. What meridian does it approximate? At any
location, however, all dates (days) begin and end at midnight.
Using the time wheel, follow a day (Sunday) around the Earth:
a. At one instant after midnight the beginning of Sunday emerges from the AM side
if midnight (180 degree meridian).
b. As other places pass midnight, they will also pass from Saturday to Sunday.
c. Turn the time wheel until 165 degrees East is at midnight. Sunday is now
between midnight and the International Date Line. The rest of the Earth still has
Saturday.
d. Continue the Earth’s rotation (W to E) until the 180 degree meridian is at noon.
Sunday now is from 0 degrees to 180 degrees of the eastern hemisphere. Half
of the Earth has Sunday and the other half Saturday.
e. Continue the Earth’s rotation until 180 degree meridian returns to midnight.
Sunday now has arrived everywhere on the Earth, but as the 180 degree
meridian passes midnight Monday begins.
f. How long has Sunday been somewhere on Earth? (13)
g. How long will it take Sunday to disappear and every place to have Monday?(14)
h. How long is any one day or date on Earth? (15)
To find time and date at any location when the time and date is know at one location,
find the distance in degrees between them and divide by the speed of the Earth’s
rotation (15 degrees/hour). (If using standard time, use the central meridian of the
time zones.) This will give the difference in time between the locations and it will
then be necessary to add or subtract depending on their relative positions. If the
new time is past midnight, then the date becomes the next day.
16. When it is 9:00 A.M. watch time (standard time) December 31 in York, what
time and date is it in Calcutta, India (90 degrees east longitude)?
17. If your friend in Viet Nam (120 degree East) wanted to call you here at school
(75 degree) and had written that he would at 3 P.M. Sunday his time, at what
time could you expect the call?
18. A plane leaves New York for a five hour flight to Los Angeles at 9:00 P.M.,
December 31. At what time and date will it arrive in CA?
19. The pope is planning on broadcasting a message to the world at noon standard
time on Christmas day from Rome (12 degree East). At what time could we
tune in our short wave radio to hear it?
20. A military transport is flying to Tokyo (135 degrees East) from San Francisco
(120 degrees West). If it leaves San Francisco at 7:00 A.M., January 1, and the
flight duration is 10 hours, at what time and date will it arrive in Tokyo?
21. In traveling from the United States to Japan, I cross the International Date Line
at 6 P.M. Tuesday December 31. What does new time and date become?
22. In traveling from Japan to the United States, I cross the International Date Line
at 6 A.M. Wednesday, January 1. What does my new time and date become?
Name:
Date:
TIME AND DATE LABORATORY ACTIVITY
ANSWER SHEET
(Please record your answers clearly and completely. Thank you)
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