Why Is Alaska So Cool? Sunlight Intensity Accumulator
Activity 8: Investigation in Sunlight IntensityPart 1: Collecting Data
Guiding Question
Why is Alaska so cool (with all that daylight)?
Prediction of results
Why do you think Alaska is so cool?
Objectives
After completing this investigation, a student will be able to describe a procedure by which sunlight intensity may be measured, recorded, and modeled mathematically; and will infer a provisional answer to the guiding question.
Materials
TI-83 Plus, CBL, light sensor, 1 m wooden dowel or other stick, electrical or plastic tape, daily log, program CBL/CBR already in the calculator.
Introduction
In this investigation, students from various locations will collect solar intensity data by means of a TI-83 Plus calculator and CBL unit. The data will be collected at noon on the equinox (or as near to that date as possible considering weather) from various stations, and will be correlated with latitude and weather conditions. The reason for collecting data on the equinox is that this mitigates duration variation.
Variable conditions we anticipate affecting solar intensity include the following: weather (degrees of cloudiness and of haze), latitude, relative distance from the sun (to a minor degree), and distance of light travel through earth’s atmosphere.
As we apply computational science to the collected data, we expect to discover a mathematical model that reasonably accounts for the data, and that will adequately predict intensity for other latitudes.
General Plan
1. A week before the equinox: Complete a trial run of the investigation following the instructions exactly, in order to know what to expect from your equipment and to eliminate problems for the day of the actual investigation. You will use the CBL to collect sunlight intensity samples automatically for two hours, from one hour before through one hour after solar noon. Use the determination of solar noon that you found from the Solar Angle investigation. You will also record data for the solar angle and observation of sky conditions during the time you are sampling the sunlight data.
a. Record your activities in your daily log, and also indicate any difficulties you had in following the procedure.
b. Record the data in a table as described on page 110.
2. On the first sunny day after within a week of the equinox, compete the following.
a. Two hours before solar noon – Gather the instruments you will be using, and set up your equipment so that you are ready to conduct sunlight intensity data collection for a two hour period.
b. One hour before solar noon – begin collecting sunlight intensity data following the instructions below beginning with the section title Rate of Sampling. Continue collecting the data through solar noon until one hour after solar noon.
c. Measure the solar angle at the beginning of your data collection, at the midpoint of the data collection, and at the end of the data collection.
d. Observe and record the sky conditions at the beginning of your data collection and every 15 minutes during the data collection, or as necessary as the conditions change.
e. One hour after solar noon – stop collecting solar intensity data, disassemble and pack equipment.
f. In your daily log, summarize what you have done today.
g. Record the data in a table as described on page 110.
3. On the day of the equinox (or first clear day after it):
a. Repeat steps a-g above.
b. Determine which set of data best represents the sunlight intensity on a clear day and use that data.
4. Keep a daily log for the course of the data collection. Include the date, the chronological time you began the collection, the times when you re-aimed the light sensor, and sky conditions (clear, hazy, cloud passing by, and so on).
5. After data from all stations has been collected, your teachers will distribute the information. You will then analyze the collected and compiled data, performing a regression analysis on it, answering questions, and reaching appropriate conclusions.
Rate of Sampling
When you collect samples of data at different times or places of the same phenomenon, this is called “sampling.” You will be taking samples of sunlight intensity over a period of time, every so often. In the course of setting up the calculator’s sampling program, you will need to indicate the number of samples you will take and the time interval in seconds between data samples.
In order to help make sure that the data are not spurious or inappropriate, you will take a number of samples, one sample every five (5) minutes over a two (2) hour span. How many samples will you take, and what is the time interval in seconds between samples, then? The following equations solve the questions:
Number of samples = 2 hr x 60 min/hr / 5 min = 120 min / 5 min = 24;
Time interval in seconds = 5 min x 60 s/min = 300 s.
So, you will take 24 samples with a time interval of 300 seconds between samplings. When the sampling is completed, you will record your data and find the average of the values of your samples for the light intensity at solar noon.
Equipment Setup
Please gather the equipment indicated in the materials section on the first page of this lesson plan.
Aiming the Light Sensor to the Sun
1. This investigation needs to take place in direct sunlight, without any shadows whatever throughout the duration of the data collection (if at all possible). Conduct the data collection in a place where you will have unobstructed view of the sun for the two hour time interval. Do not conduct it through window glass, though you might be able to use an open, unscreened window. The better location is outside in an open area. If you live in a place where the sun does not shine directly, go to a nearby place such as a park or field.
2. Throughout the sampling time for sunlight intensity, you will need to have the light sensor aimed as directly toward the sun as you can. The sun will appear to be moving through the sky (through a small arc, however) over the two hours, so you will need to make periodic adjustments to the light sensor’s orientation toward the sun. CAUTION: Do not look directly at the sun! One way to help make sure the light sensor is at the best aim is to have the light sensor create the smallest shadow possible at a given height from the ground.
3. To accomplish this, you may use a wooden dowel or suitable stick; a wiener roast type of stick would be fine as long as it is rigid enough not to bend. See Figure 1. If the ground is soft enough, press the dowel into the ground. Otherwise support it so that it will stay in an upright position. Aim the light sensor toward the sun, and tape it to the dowel in that position. You can fine tune the aim by pivoting the sensor up or down as necessary and by turning the dowel right or left. The smaller the shadow, the more directly it is aimed to the sun.
4. Once the data collection has begun, please do not change the height of the sensor on the dowel. You may turn the dowel or pivot the light sensor, however.
5. During the sampling process, check to see that the light sensor is aimed appropriately every fifteen (15) minutes.
6. You do not need to hold the CBL unit and calculator in your hands the whole time, but please do not place them directly on the ground. Moisture is not a friend to electronic equipment. You may place your equipment on a plastic sheet on the ground or a table if one is handy.
7. Do not leave your equipment unattended. Stay with your equipment until you have completed data collection and have placed your equipment in its storage area.
Readying the Calculator and CBL
As you have connected the calculator and CBL in other investigations, please do so again. You will run the APPS program called CBL/CBR in order to collect sunlight intensity data. (This application is described in the TI-83 Plus Manual on pages 14-16 through 14-26.)
1. Turn on the calculator, and press twice, then press the blue key. You have usually used the PRGM key to find programs, but this is a different type of program. It works as other ones you have used. Your screen should look like the following:
2. Choose 2:CBL/CBR, and the next screen is:
3. Follow the instructions, and the next screen is:
4. Since we are planning to log data over a period of time, choose 2:DATA LOGGER, and the next screen shows (your screen may have different values):
5. You have several parameters to set on this screen.
a. Press the cursor key to choose Light and press .
b. Press cursor key to #SAMPLES:, and type 24, press . The cursor drops automatically to the next line.
c. At the INTRVL(SEC) line, type 300. Press . The cursor automatically drops two lines.
d. At the PLOT line, choose RealTime and press .
e. On the DIRECTNS: line, choose ON, and .
The cursor drops to GO…, and the resulting screen must look like the following:
If your screen has other values or other selections than the screen above, then move the cursor (up or down), select and enter the parameters (selections and numbers) as described in Item 5 a-e, above.
6. When all the values and choices are correct, press . Follow the connection instructions as you have in other investigations.
7. When the connections between the probe, CBL, and calculator are complete and you have received the STATUS: O.K. message, press . The next screen is:
8. You are now ready to begin collecting light intensity samples.
Sampling Light Intensity
1. When the time is right (one hour before solar noon on the summer solstice), do as the message summons you to do: Press . The screen changes to show a coordinate plane, and nothing else seems to be happening. But in fact, the program is running and you are collecting sunlight intensity samples, one every 300 seconds for the next two hours.
2. In your daily log, note the actual date and chronological time you pressed the Enter key to start sampling.
3. Note that the CBL unit will show values in its screen that will be updated every five minutes, and it will flash the word SAMPLING for the entire time. You may also see a short moving line in the upper right hand of the calculator screen, to indicate that it is working. Periodically, a dot appears on the coordinate plane corresponding to the sampled light intensity. You will have 24 of these dots in place by the end of the sampling period. They will appear in a graph on the screen. (The program sets up Plot 1 to plot these points as they are collected.)
4. What if the CBL or the calculator is not doing what the last paragraph said? If things are not working properly, turn everything OFF, and start over with “Readying the CBL and Calculator” in Item 1 above. Be sure to note in your daily log that you had to start over, and log the time when you actually began the sampling properly.
5. When your data collection is completed, please turn off the CBL and disconnect it from the calculator. Place the CBL, light sensor, and link cable in the protective case. You will not need to use the CBL unit or light sensor. Indeed, you have now completed all the activities in which these are used. If the calculator still shows the moving dots in the upper right corner of the screen, press to stop the program from running.
6. Did your collection go well? If so, congratulations – good job!
Recording and Sending Collected Data
When the program collected the sunlight intensity, it stored the data in two lists named LIGHT and TLGHT (for “light intensity” and “time interval,” respectively). You cannot see these lists directly, but you can copy them to L1 and L2 lists, and then you can see them.
The following procedure will step you through the process so that you can read the lists. These instructions will not explain why you are doing the procedure, only that these are the steps to take. If steps are not self-evident, and you are curious about them, you may read the TI-83 Plus Manual, page 12-11, for an explanation of Entering a List Name in the Stat List Editor.
1. Turn on the calculator and press . You are in the list editor screen and it will look something like the following, but may have different values in the lists:
2. Press to move the cursor up to highlight the list name L1. Press to access the LIST NAMES menu and the screen shows: