Seasons worksheet
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University of Michigan *
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105
Subject
Geography
Date
Dec 6, 2023
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docx
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Uploaded by BarristerKingfisher3714
The Seasons: Worksheet
In this activity, you will explore how the Sun's position and apparent motion vary seasonally and depend on the observer's
latitude. Before class, please review Figure 1 in the introduction and the following terms from the Coordinate Systems
activity.
You will be using the local sidereal time (LST; see the Timekeeping and Telescopes at the Detroit Observatory Activity) as
an approximation of solar time. In the planetarium, the LST is determined by reading the RA on the equator that is
crossing the meridian (see Figure 1). There are tick marks every 10 minutes, with longer marks for the hour and half hour.
The date is based on the Sun's position on the ecliptic. In the planetarium, the ecliptic is labeled with the calendar dates,
but watch the direction: the Sun moves eastward through the stars! Note that the position of the Sun is only accurate to
about 2 days (e.g., the computer may set the Sun's position for March 21, but the Sun may actually appear to sit on March
19.) When asked for the date, record the position of the Sun that you observe, but keep this inaccuracy in mind when
doing the activity.
The cardinal directions (N, E, S, W) are azimuthal directions on the horizon, where the north and south cardinal points are
defined by the intersection of the meridian with the horizon (Figure 1). East and west are defined to be 90 and 270 degrees
clockwise on the horizon, when facing north, which is 0 degrees azimuth. When facing down toward the Earth, east is to
the right of north. However, when facing the sky, east will appear to the left of north, instead of to the right!
Azimuth is measured in degrees from the north cardinal point on the horizon (0 degrees azimuth), toward east. It is
represented by the horizontal arrow in Figure 1. The azimuthal direction can be given roughly, using the cardinal
directions. For example, an object's azimuthal direction can be estimated as north-northeast (NNE), or west-southwest
(WSW). In this activity, the azimuthal direction is used to determine rising and setting directions for celestial objects.
Altitude is measured in degrees above the horizon, and is represented by the vertical arrow in Figure 1. It is most easily
measured when an object is on the meridian because the meridian is exactly perpendicular to the horizon. In the
planetarium, it is conveniently marked in degrees. Please note: The wall in the planetarium cuts off the horizon 2 degrees
above the true horizon.
Page 1 of 5
Part 1: Navigating the Planetarium
The questions in this first part are meant to help you understand how to get the information you need for the rest of the
activity. Please think about
how
you get the answers as you go.
Sunrise
1.
What is the local sidereal time?
2.
From what azimuthal direction is the Sun rising?
Local noon
3.
What is the date?
4.
Is the Sun
above
,
below
, or
on
the celestial equator? (circle one)
5.
What is the altitude of the Sun when it is on the meridian?
6.
Fill in the appropriate row in Table 1.
Table 1: Observing the Sun from Ann Arbor
Rise time
Rise position
(azimuthal
direction)
Date
Altitude at
noon
Set position
(azimuthal
direction)
Set time
Hours of
daylight
March
Equinox
June
Solstice
September
Equinox
December
Solstice
Part 2: Ann Arbor
Page 2 of 5
8.
Your GSI will show the Sun's motion on key seasonal dates. Use the same methods that you used in Part 1 to fill
out the remaining rows in Table 1.
9.
From Table 1, compare the azimuthal directions where the sun rises and sets for the equinoxes versus solstices.
10.
Which season starts on each date in Table 1, in Ann Arbor?
March Equinox:_____________
September Equinox:_____________
June Solstice:_____________
December Solstice:_____________
Part 3: Other Latitudes
The GSI will now present the sky from other latitudes at noon on the June solstice. Record the position at which you see
the Sun at each location in Table 2.
Table 2: Observing the Sun on the June solstice
Latitude
Altitude at noon
Azimuthal direction at sunrise
Azimuthal direction at sunset
North Pole
Arctic Circle
Tropic of Cancer
Equator
Tropic of Capricorn
10.
Which season starts on each date in Table 1, in Santiago, Chile?
March Equinox:_____________
September Equinox:_____________
June Solstice:_____________
December Solstice:_____________
Concluding Questions:
Complete any sections of Table 1 that have not been filled in. Figures 2 and 3 in the Introduction may be helpful in
answering some of the following questions.
Page 3 of 5
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1.
Reviewing your answers to Part 3, how does your latitude affect the observed maximum altitude of the Sun in the
sky on the summer solstice? Be as specific as you can. Explain how this relates to the average temperatures at the
equator and poles.
2.
Compare the number of daylight hours in Ann Arbor in summer and winter. Together with your answer to the
previous question, explain how these factors are related to the average temperature in these seasons.
3.
If you are standing on the North Pole on the December solstice at noon, can you see the Sun? Explain.
4.
Which latitude has the least variation in the length of day and night, throughout the year: the equator, Tropic of
Cancer, or arctic circle? Which has the most? Explain.
Page 4 of 5
5.
Using Figure 3 in the Introduction, show how to find the latitudes of the arctic and antarctic circles, in degrees.
Please copy the relevant parts of Figure 3 below and explain clearly, showing the results.
Last updated 02/18/21 MSO.
Copyright Regents of the University of
Michigan
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