Find a
Select grade level(s) Select resource type(s) Select collection(s) Select standard(s) Skip navigation Digital Library for Earth System Education
Digital Library for Earth System Education
Search tips
Discovering Planet "X" DLESE Reviewed Collection
This activity and demonstration teaches the concept of parallax (the apparent movement of an object caused by a change in the viewer's position) and relates the concept to a real-world astronomical event, ­the discovery of Pluto. It employs the Blink Comparator, an online simulation illustrating the technique used by Clyde Tombaugh to discover the ninth planet on February 18, 1930.
Intended for grade levels:
  • Intermediate (3-5)
Type of resource:
  • For the classroom:
    • Classroom activity
    • Lesson plan
  • Physics
  • Space science
Technical requirements:
Adobe Acrobat reader
Cost / Copyright:
No cost
Copyright and other restrictions information is unknown.
DLESE Catalog ID: DLESE-000-000-009-198
Educational standards:
  • National Science Education Standards (NSES):
    • K-4:
      • B - Physical science:
        • Position and motion of objects
      • D - Earth and space science:
        • Changes in earth and sky
        • Objects in the sky
Related resources:
This resource requires 'Blink Comparator'
Resource contact / Creator / Publisher:
Contact: Kerri Beisser
Space Department Education and Public Outreach Office
Johns Hopkins University Applied Physics Laboratory