Introduction to Physical Geography
Instructor/Chaddock
Homework Assignment #2
Page 15
Homework Assignment #2:
Tracking the Sun: Earth—Sun Relations as Experienced in San Diego
Part 1:Tracking the Sun
In this exercise we are going to look at seasonal variation in the timing and relative
position on the horizon of sunrises and sunsets. This exercise is designed to give you a practical
experience in understanding seasonal Earth—Sun relationships across space and time.
Once a week, for four weeks, you are to record the timing and relative horizontal position
of 4 sunsets or sunrises. If you choose to do sunrises, please only watch sunrises, do not mix and
match.
Choose a viewing area that has a clear sight to the horizon. Make sure there are some
permanent fixtures such as hills, buildings, cell towers, or trees on the horizon to act as points of
reference. The ocean is not a good horizon for this exercise. A better choice might be
somewhere like the top of Mt. Helix where there is a clear sight to the horizon, and the coastline
and downtown skyline make for good points of reference (Cuyamaca College also serves as a
good observation site, especially for sunrises.)
At sunset (or sunrise) note the time and make a sketch of the sunset (or sunrise) from
your vantage point. You should make your observations at a oblique angle—DO NOT LOOK
DIRECTLY AT THE SUN AS THIS CAN BE HARMFUL TO YOUR EYES. Be sure to
make your observations from the same spot each time, do not move around. The time of sunset
(or sunrise) should change each week, as should the relative position of the sun with regard to the
horizon. For the best results, you should space out your observations at least 4-5 days apart;
anything less than that and the changes you are tracking may not be as readily observable.
Please get started as soon as possible as you only have 6 weeks to make 4 observations and there
will most likely be some cloudy days when observations are not possible; if you miss a day, just
make your observation on the following day—as long as there are at least 4-5 days in between
observations you should be ok. Please record the time of sunset (or sunrise) and make your
sketch in the boxes provided on page 2. Follow the example below, and please do not hesitate to
make an appointment to see me if you need any help with this assignment.
Example: Week 2: Date ___1/27_____ Time:___5:15 pm __am/pm Location:___Suncrest_
Introduction to Physical Geography
Instructor/Chaddock
Homework Assignment #2
Page 25
Week 1: Date ____________ Time:___________ __am/pm Location:___________________
Week 2: Date ____________ Time:___________ __am/pm Location:___________________
Week 3: Date ____________ Time:___________ __am/pm Location:___________________
Week 4: Date ____________ Time:___________ __am/pm Location:___________________
Introduction to Physical Geography
Instructor/Chaddock
Homework Assignment #2
Page 35
After completing all four observations, please answer the following questions:
1.
In terms of the timing and relative position of the sunset (or sunrise), please describe the
changes that have occurred through your 4 observations (i.e. does the sunset or sunrise occur
progressively earlier or later through your 4 observations?; and does the sun’s position at the
horizon migrate to the south or the north through your 4 observations?)
2.
In terms of Earth revolution, axial tilt, and seasonal migration of the subsolar point,
please explain why the timing and relative position of the sunset (or sunrise) changed through
your 4 observations.
Part II: Noon Sun Angles
As we saw in Part I, the sun’s position relative to the horizon at sunrise and sunset
changes on a daily basis. At the same time the maximum noon sun able is also changing. In this
exercise we will calculate the maximum noon sun angle on the same 4 days as our sunrise/sunset
observations in Part I. Below is the equation for calculating the maximum noon sun angle for
any day of the yar at any location on Earth, as well as two sample problems using Denver, CO
as an example.
To calculate noon sun angles we will use the attached analemma on page 5. The
analemma shows the solar declination (the latitude at which the sun is 90˚ above the horizon at
solar noon, also known as the subsolar point) for each calendar day of the year. We will use
Denver as an example for calculating the noon sun angle on October 21 and May 15. The
equation we need is given below:
90˚ - [the distance in degrees between your latitude and the solar declination (subsolar point)]
If you are in Denver on October 21 the noon sun angle can be calculated as follows:
90˚ - (50˚) = 40˚
>>The solar declination on October 21 is 10˚ S. Latitude and Denver is 40˚ N. Latitude, so the
distance in degrees between the two locations is 50˚.
If you are in Denver on May 15 the noon sun angle can be calculated as follows:
90˚ - (22˚) = 68˚
>>The solar declination on May 15 is 18˚ S. Latitude and Denver is 40˚ N. Latitude, so the
distance in degrees between the two locations is 22˚.
*See information in your textbook for further discussion on the use of the analemma.
Introduction to Physical Geography
Instructor/Chaddock
Homework Assignment #2
Page 45
Using the same method as above, please calculate the noon sun angle to within 0.5˚ for the 4
days you made your sunrise/sunset observations (use a latitude of 33˚ for all San Diego
observations; please show your work in the space provided.)
Observation #1
Date:__________________________
Noon Sun Angle:________________
Observation #2
Date:__________________________
Noon Sun Angle:________________
Observation #3
Date:__________________________
Noon Sun Angle:________________
Observation #4
Date:__________________________
Noon Sun Angle:________________
After calculating the noon sun angle for your 4 observation days, please answer the question
below:
In terms of the noon sun angle and the solar declination, please describe the changes that
occurred over the course of your 4 observations, and please explain why these changes
occurred (i.e. did the noon sun angle increase or decrease through your 4 observations?;
did the solar declination move north or south through your 4 observations, and why was
this significant in the changes you observed?)
Introduction to Physical Geography
Instructor/Chaddock
Homework Assignment #2
Page 55