Name
Class
Partner
PHYS1411/1403
The Seasons
Objective
In this Lab activity, we will explore how seasons on Earth occur and what factors control the change in seasons
by collecting data in the planetarium. Please review the relevant text we discussed on seasons.
Data Collections and Measurements:
1. Your SI will show you the Sun on the 21st of each month going from Sunrise to Sunset. He / She will
bring up the Cardinal points, Equatorial grid, Alt-AZ grid. Learn how to read the positon of the Sun on
both grids as it rises, crosses the meridian and sets in the west.
2. Record the following data in Table 1.
a. The azimuthal position of the Sun at Sunrise and Sunset. Record the data in degrees north (N)
or south (S) of east for Sunrise and degrees north or south of west for Sunset.
b. The noon time altitude of the Sun.
c. The noon time declination of the Sun (degrees above or below the equator).
Making Graphs:
1. Complete column DN using information from column DM, the number of days past the first day of
January.
2. Using your data from Table 1. Plot the altitude of the noon Sun for 21 st of each month on graph A (DN
vs A). Note down your local latitude as well.
3. Using your data from Table 1. Plot the declination of the Sun for 21 st of each month on graph B (DN vs
D).
4. On graph B label the date for vernal equinox, autumnal equinox, summer solstice and winter solstice.
Data Analysis:
1. Using your data on sunrise and sunset, on when does the longest day occur. When does, the shortest
day occur?
1
2. What is the difference in degrees between the sunrise positon on the longest day and sunrise positon
on shortest day?
3. Using graph A, find the direction in which the Sun appears to move. Why do we call it “appear”?
4. Determine the amplitude in both graph A and B. Amplitude is the difference between high and low
points divided by 2.
5. What is the significance of amplitude?
6. What is the amplitude if Earth axis tilt was 10 degrees?
2
7. What is the amplitude if the Earth’s N axis always pointed away from the Sun?
8. If the Earth’s axis is always pointing away from the Sun, what would be its consequences on the
seasons? Explain.
9. Subtract the declination of each month from its latitude (A-D = X). What do you find? What might be the
significance of this number?
10. Now subtract X from 90. What is the significance of this number?
3
Table 1
Date -21st
day
Of Month
Days in
Month
(DM)
January 2016
February
March
April
May
June
July
August
September
October
November
December
January 2017
February
2017
March 2017
31
29
31
30
31
30
31
31
30
31
30
31
31
Number
of Days
passed
(DN)
21
Altitude (A)
at noon
Declination
(D)
at noon
Sunrise
Position
Sunset
Position
52
28
31
Average X =
4
A-D =X
Graph A
90
80
70
Altitude
60
50
40
30
20
10
0
0
50
100
150
200
250
Days
5
300
350
400
450
500
Graph B
90
80
70
Declination
60
50
40
30
20
10
0
0
50
100
150
200
250
Days
6
300
350
400
450
500