Lab Exercise Three: Time, Radiation, Temperature

1. a).The distance around the earth at the equator is approximately 24,900 miles. Since the earth makes one rotation in about 24 hours, a person on the equator is moving with the earth at what speed (in miles per hour)?

b).Persons living anywhere other than the equator would be traveling at a lesser speed. Why?

c).At the latitude of Memphis (35˚ N), one degree of longitude is known to be approximately 57 miles. At what velocity is Memphis moving with earth rotation (in miles per hour)?

d). Although places on earth at different latitudes have different rotational velocities, they nevertheless all have the same angular velocity, because they rotate through 360 degrees of longitude in 24 hours. Therefore they have an angular velocity of how many degrees per hour?

2. The time of day is determined by earth rotation. The meridian of longitude that is turned directly toward the sun is at the noon position. The meridian directly opposite is at the midnight position. The time where you are depends on where you are in the earth’s rotation. The angular velocity of the earth’s rotation is such that the earth spins through 15 degrees in 24 hours.

a).How many minutes does it take for the earth to spin through one degree of longitude?

b) Local or solar time is based on the position of the sun and differs for each degree of longitude. Therefore, if we used solar time as our time method, every single place with a different longitude would be experiencing a different time. Using the solar time system, indicate in Figure One the boundaries of daylight, when the sun is vertically overhead at the equator at 0˚longitude. To do so, mark and label the longitude experiencing sunrise and the longitude experiencing sunset.

c). On Figure One, what is the local/solar time at each of the following longitudes?

90˚E?10˚W ?

90˚W? 1˚E ?

108˚E?Duluth?

d) Suppose that one hour passed. Where would the boundaries of day and night be?

3. To avoid the havoc of every single degree of longitude having its own unique time of day, world time was standardized into a system whereby each fifteen degrees of longitude is in a time zone. The time of day is the same throughout the time zone. This type of time is called standard time.Standard time within each time zone is based on the solar/local time of the Central Meridian of the time zone. All longitudes in the time zone therefore have the same time as the solar time of the Central Meridian.

a) What time is it on our clocks (standard time) in Duluth when it is noon(solar) at the Central Meridian for our time zone?

b) What time is it on our clocks in Duluth when it is solar noon in Duluth?

c) Since each time zone is fifteen degrees wide, how many time zones are there?

d) Using the time zone map in your textbook and an atlas if necessary, determine the time AND day for the following place, given the time in the second city listed.

*Hour and day in San Francisco when it is 2pm Saturday in Bogota, Colombia

* Hour and day in New York when it is 8 am Monday in London?

* Hour and day in Turkey when it is 7 pm Wednesday in Cuba?

* Hour and day in Hawaii when it is 3 am Friday in Moscow?

* Hour and day at a place out of town where you have a friend (or family) when it is right now in Duluth?

e) On Figure Two, fill in the 20 blanks with the hour and day for each. (On the Figure, I.D.L. stands for International Date Line, and the dotted lines are Central Meridians.

4. Using Figure 3 and a ruler, draw and label on each of the 4 diagrams :
a. North and South Poles
b. Equator
c. Tropics of Cancer and Capricorn
d. Circle of Illumination(Shade in the portion of Earth experiencing darkness) .
e. Arctic and Antarctic Circles

5. For each of the following dates, list the latitudes at which the direct and tangent rays touch the earth?
a. June Solstice
b. September Equinox
c. December Solstice
d. March Equinox

6. Using the following equation, calculate the sun angle on June Solstice for the 3 locations below.

Sun angle = 90 - (degree difference between latitude and subsolar point)

a. Bogota, Colombia: latitude 4.5 degrees North
b. Duluth: latitude 46.5 degrees North
c. Johannesburg, South Africa: latitude 26 degrees South

7. The analemma (Figure 4) graphs the subsolar point for each day of the year. The declination is the latitude of the subsolar point. Use the analemma to determine the subsolar point for today's date.

8. Now, use the equation from #6 and the analemma to answer the following:

a. What is the subsolar point on January 21? What is the angle of the noon sun on January 21 at 49 degrees South?

b. If, on November 23, the angle of the noon sun at a certain location is 80 degrees, what is the latitude of that location?

9. a)Following your instructor's directions, make an isotherm map of the temperature data which are plotted on Figure 5 , a map of eastern North America. A 60 degree isotherm has been drawn on the map for you. Draw isotherms of 30, 40, 50, 60, and 70 degrees and label all isotherms. (Notice that some isotherms may be repeated on the map. For example, you may have two 60 degree isotherms). After completing the map, answer the following questions.

b)What season do you think this map represents? Why?

c)Where is the strongest temperature gradient on your map? Where is the weakest temperature gradient ?