Students conduct a simple experiment to investigate reflection and absorption of visible light by dark and light materials. They learn that the term albedo refers to the ratio of how much incoming light is reflected by a substance and explore the albedo values of different types of surfaces on Earth. Based on the results of the experiment, they make inferences about the important role that snow plays in regulating Earth’s climate.
Importance of snow: Cooling the planet. 2020. Our Winter World website. http://ourwinterworld.org/importance-of-snow/
Snow science: Optical properties of snow. 2020. Our Winter World website. http://ourwinterworld.org/snow-science/properties-of-snow/#optical-properties
Changing Albedo Values. My NASA Data. https://mynasadata.larc.nasa.gov/basic-page/changing-albedo-values. Includes links to:
- Earth’s Energy Budget Includes Albedo (Why does the Sun Matter for Earth’s Energy Budget? video)
- When do albedo values change? (Climate Bits: Albedo video)
- Why does NASA study albedo? (Global temperature anomalies from 1880 to 2018 video)
Albedo – Terrestrial Albedo. 09.03.2021. Wikipedia. https://en.wikipedia.org/w/index.php?title=Albedo&oldid=1042141005
Earth’s Energy Balance (online interactive simulation). 2021. University Corporation for Atmospheric Research (UCAR) Center for Science Education. https://scied.ucar.edu/interactive/earths-energy-balance
Included in kits unless otherwise noted
Kits include enough materials so that four groups of students can do the experiment at the same time.
● Black felt pockets (4)
● White felt pockets (4)
● Dial stem thermometers (8)
● Clamp on lamps with reflector shades (4)
● 60 Watt Incandescent light bulbs (4)
● Schools might need to provide extension cords and/or power strips for lamps.
1. Experiment set up
Set up four stations. For each station, you will need a desk, table, or other flat surface; 1 black felt pocket; 1 white felt pocket; and 1 clamp lamp with light bulb.
Lamps should be positioned so that they shed light on the surface below them, upon which the two felt pockets will be placed side by side. The lamps should be centered over the surface so that each pocket receives the same amount and intensity of light. If there are no good options for affixing the clamp lights above desk/table height, you can clip them to the edge of the desk and set up the felt pockets on the seat of a chair underneath.
Felt pockets should be oriented so that the thermometer dial can be read easily while the thermometer stem is inserted into the pockets.
Check to make sure the two thermometers at each station read within a degree or two of each other. If they don’t, refer to the instructions on the packaging to calibrate them so that they start at the same temperature.
2. Experiment introduction and hypothesis development
Introduce what the experiment will entail without presenting too much information about the underlying science.
Ask students to develop a hypothesis based on their everyday life experience as to whether and in which direction they think that the temperatures will change (go up, go down, or don’t change) and whether and how the temperature changes will be different between the black and white felt pockets (e.g. one will go up, one will go down; both will go up but the black one more so than the white one, etc.).
Ask students to write down their hypotheses in a notebook or data sheet and to including their rationale, whether based on life experience, knowledge of underlying scientific concepts, or intuition.
3. Experiment steps
Students at each station should follow these steps in sequence:
1. Before turning the lights on, insert a thermometer into each pocket (one black, one white) so that the dial is facing them and the stem is fully covered by the felt. Ensure that the thermometers are placed in such a way that the lamp is centered over them, providing an equal amount of light to each pocket.
2. Read the initial temperature of both thermometers and record them in a notebook or data sheet.
3. Turn on the light. Without touching the materials, watch the thermometers for changes in temperatures.
4. After five minutes, check the temperatures, being sure not to touch the thermometers or remove them from the pockets. Record the temperatures in a notebook or data sheet, being careful to note which temperature is for the black felt pocket and which is for the white felt pocket.
5. If there is a substantial temperature difference between the two thermometers after five minutes, you can end the experiment. However, if there has only been a small change in temperature and/or if the temperature of one or both thermometers seems to be continuing to change rapidly, wait another three to five minutes and record the temperatures again.
3. Share and discuss results
Ask each group to calculate how much the temperature of the white pocket and the black pocket changed during the experiment by subtracting the starting temperature from the ending temperature for each.
Compile results from all groups by having a representative of each group enter their temperatures in a whole class chart (e.g. created by the teacher on a white board) or by sharing aloud the starting and ending temperatures that they recorded for the white and black pockets. Note any discrepancies in results and check to find out if everyone followed the same experimental protocols.
Did the results support or conflict with their hypotheses? If so, do they have any thoughts about what might account for the results that they had not considered in developing their hypotheses?
If they haven’t already done so, ask students to share examples from their life experience that relate to the experiment. For example, if they have ever worn black or dark clothing versus white or light-colored clothing on a hot, sunny day, which color of clothing made them feel warmer? Has anyone had the experience of walking barefoot on black asphalt or lighter colored surfaces?
4. Connecting scientific concepts: Explaining absorption and reflection
Refer to background/reference information.
Light is either reflected or absorbed by an object or substance.
The word albedo refers to how much of the incoming light that an object receives is reflected by that object. More reflective objects have higher albedo values, and less reflective objects have lower albedo values.
Albedo values range from 0 to 1. An object that absorbs all incoming light and reflects none of it has an albedo value of 0. An object that reflects all incoming light and absorbs none of it has an albedo value of 1.
5. Applying what we’ve learned: Albedo, snow, and Earth’s climate
Display an aerial photograph or photograph of the Earth from space and notice the different colors of Earth surfaces. Which areas would the students expect to have high albedo values and which would have low albedo values?
6. Optional extension for advanced learners
A. Earth’s Energy Budget
Earth’s albedo is an important part of Earth’s energy budget, which describes the net amount of energy absorbed by the Earth based on its incoming energy and outgoing energy flows. Earth’s energy budget determines the temperature of the Earth.
This online interactive from UCAR Center for Science Education allows you to manipulate amount and brightness of incoming solar energy and the albedo of Earth’s surface and see how changes to those values affect Earth’s temperature: https://scied.ucar.edu/interactive/earths-energy-balance
B. The electromagnetic spectrum and visible light
NASA Science. 2021. Introduction to the Electromagnetic Spectrum (video). National Aeronautics and Space Administration (NASA). https://science.nasa.gov/ems/01_intro
NASA Science. 2021. Visible Light (video). National Aeronautics and Space Administration (NASA). https://science.nasa.gov/ems/09_visiblelight
Butcher, G., Mottar, J., Parkinson, C.L., and Wollack, E.J. 2016. Tour of the Electromagnetic Spectrum. National Aeronautics and Space Administration (NASA). https://smd-prod.s3.amazonaws.com/science-pink/s3fs-public/atoms/files/Tour-of-the-EMS-TAGGED-v7_0.pdf
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