Starry Night-The Seasons
In this laboratory, you will explore the patterns of the Sun in our sky and determine which
factors are important, or unimportant, in creating our seasons.
What causes our seasons? In this lab you will examine three of the factors involved in
determining when seasons take place. These factors are distance from the Sun, the height of the
Sun in our sky, and the length of daytime. We’ll be focusing on the seasons in Los Angeles.
1. The orbit of the Earth around the Sun is not exactly spherical, but is slightly elliptical.
Therefore there is a point in the Earth’s orbit closest to the Sun, perihelion, and a point in the
Earth’s orbit farthest from the Sun, aphelion.
2. Because the Earth’s rotation axis is tilted with respect to the axis of revolution by 23.5º, the
height of the Sun in our sky changes throughout the year.
3. This tilt also causes parts of the Earth to experience longer times of daylight than others.
While all of these factors will affect our seasons in some ways, which factors are more important
than others? Or are they all three equally important?
Figure 5.1 shows a graph of average high and low temperatures for each month in Northridge.
Record the average high temperatures (orange row) for each month in the temperature column.
We’ll this quantity to describe the seasonal changes.
Open a web browser to the Solar Data Website.
Scroll down to the large table of data below. Set the month to January and the year to the current
As an EXAMPLE: highlight the 4th which will expand the information. The online table should
look much like that in Figure 5.2 for January of 2019.
Graph of average high and low temperatures for each month for Northridge.
Solar Data Table for January 2019.
1. The length of the day, DAYLENGTH, is found under the Daylength column. No surprise
there. It is listed in hours and minutes. We will round these to the nearest minute, thus the
Daylength would be recorded 9:58.
2. The ALTITUDE of the Sun at noon is under the Solar Noon column. It is shown in
parenthesis after the time when the Sun crosses the meridian. We want to record the decimal
point as well for these so the Altitude would be recorded as 33.3º.
3. The DISTANCE to the Sun at noon is also listed in this column to the right of the time and
altitude. The distances are given in Millions of Miles. We will use all the decimals here so
we would record this number as 91.404 Mil. mi.
Once you are familiar with how the website works record the Daylength, Altitude, and Distance,
in your data table for the 15th of each month in the current year.
Once you are finished. Highlight your birthday from this year use the information to answer the
question at the bottom of the data page.
ANALYSIS: On your data table. Do not include your birthday for this part.
1. Examine the temperatures column to find the highest and lowest values. Color in the highest
temperature red and the lowest temperature blue. These are the times of the actual seasons we
experience in Los Angeles. The hottest month is mid-summer and the coolest month is midwinter.
2. We expect more hours of daylight in hotter months. Examine the daylengths. Circle the
longest time in red and the shortest time in blue.
3. We expect the sun to be higher in the hotter months. Examine the altitudes. Circle the highest
altitude in red and the lowest altitude in blue.
4. We expect the sun to be closer during hotter months the closer the Sun the smaller the
distance. Examine the distances. Circle the smallest distance in red and the largest distance in
Use your data table to answer the following questions.
Which month is our mid-summer?
How many months before mid-summer do each of the three studied factors favor heating?
Which month is our mid-winter?
How many months before mid-winter do each of the three studied factors favor cooling?
Based on these answers, which of these three factors are the main causes of our seasons, and
which are not?
Once you are done, put your data table in a word file and submit it for grading.
1. During which month is it mid-summer (hottest temperatures) in Northridge?
2. How many months before do each of the three studied factors favor heating?
3. During which month is it mid-winter (lowest temperatures) in Northridge?
4. How many months before do each of the three studied factors favor cooling?
5. Based on your answers, which of these three factors are the main causes of our seasons, and
which are not?
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