Plotting
the Sun’s Path
Directions: Use the table to plot the path of the Sun on a particular date. The angular values represent, in order, the altitude and azimuth of the Sun as seen by an observer from latitude 36°N and longitude 84°W (i.e. from Knoxville). Choose a column and plot each value increasing in time of day on the given chart. Connect the points with a smooth curve.
|
Local time (EST) |
9/23/99 |
12/22/99 |
3/20/00 |
6/21/00 |
|
5 am |
-18°, 77° |
|
-21°, 74° |
-4°, 57° |
|
7 am |
6°, 95° |
-9°, 113° |
3°, 92° |
18°, 74° |
|
9 am |
30°, 115° |
12°, 131° |
27°, 112° |
42°, 89° |
|
11 am |
49°, 146° |
27°, 156° |
47°, 140° |
65°, 114° |
|
1 pm |
53°, 193° |
30°, 187° |
54°, 187° |
77°, 202° |
|
3 pm |
40°, 233° |
21°, 216° |
42°, 229° |
57°, 258° |
|
5 pm |
18°, 256° |
4°, 237° |
21°, 254° |
33°, 277° |
|
7 pm |
-7°, 275° |
-18°, 254° |
-3°, 273° |
9°, 292° |
|
9 pm |
|
|
|
-11°, 310° |
Compare the Sun’s path for the different dates. Imagine yourself at the center, inside the dome looking out at the Sun on those dates. Do the paths plotted seem right from your experience? Answer the following questions:
1. Which of the dates given has the most daylight hours? And approximately how many daylight hours are there on this date?
2. Which of the dates given has the least daylight hours? And how many daylight hours does this date have?
3. How many daylight hours are on the other given dates?
4. Approximately how many degrees does the Sun move along its path per hour?
5. What is the significance of each date given in terms of the four seasons?
6. Does the Sun ever pass directly through the zenith as seen from Knoxville?
7. What is the greatest altitude attained by the Sun for the paths shown? At what date and time does this occur?
8. By how much does the altitude of the Sun differ at noon on each of these days?
9. Determine the approximate sunrise and sunset times for these dates.
10. When is daylight savings time in effect? What is the purpose and how is it related to the Sun’s paths through the sky?
11. What are the points on the horizon when the Sun is farthest north? Farthest south? At what dates and times do these events occur?
On this chart:
Altitude is in increments of 10°; bold line is the horizon and center is zenith
Azimuth is in increments of 15°;
north is up.
Answers
1. June 21 – 14 hrs
2. Dec 22 – 9 hrs
3. about 12 hrs
4. 15°
5. Each date is the first day of one of the seasons, in order autumn, winter, spring summer
6. no
7. 78°, on June
21, at about
8. about 23° difference from one to the next
9. Sept
23 – 6:40 am to 6:20 pm
Dec 22 – 8:00 am to 5:20 pm
Mar 20 – 6:30 am to 6:30 am
Jun 21 – 5:40 am to 7:40 pm
10. DST is in
effect mainly in summer and fall.
Purpose is to get the most use out of the daylight hours. By setting clocks ahead we do not “waste”
sunlight hours that would otherwise occur before about
11. Farthest
north on June 21 at azimuths of 60° and 300°
Farthest south on December 22 at azimuths of 120° and 240°