Science project

UV Radiation Blocking Clouds

The goals are to test the student’s initial hypothesis about the effectiveness of clouds in blocking UV radiation through the collection of data, and then to use that data to revise the initial hypothesis (if necessary).


Does the UV Index vary with amount of cloud cover?


  • UV detector, calibrated to the National Weather Service’s UV Index
  • Materials can be found on the internet (


  1. Familiarize yourself with the various types and characteristics of clouds.
  2. Formulate a hypothesis to explain why ultraviolet radiation might pass through some clouds more easily than others, and why it might be amplified by some.
  3. Using a handheld UV detector, measure the UV Index – the strength of the solar UV radiation on a scale of 1 (low) to 11 (extremely high), at noon.
  4. Record the date, percent cloud cover, and type of clouds when you make the measurement.
  5. Collect the same data each day over the following two months.
  6. Analyze your data to determine the relative effectiveness of the various types of clouds in blocking UV radiation.
  7. Compare the results of the experiment with your initial hypothesis. If necessary revise it and make additional measurements to test the revised version.
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