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Natural Science - Year I

Unit 27: Brahe, Kepler, and Elliptical Orbits

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Lab for Unit 27

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Natural Science Unit 25 Laboratory Activity: Galileo's Observation

Goal: Repeat some of Galileo's observations of Jupiter's Moons and the phases of Venus.

Materials and Equipment:

  • Binoculars or a 4" telescope with magnification of at least 8X
  • Sky and Telescope, planetarium program, or website for planning observation
  • Sketch paper


    1. Using Sky and Telescope (or another almanac that explains when the planet will be visible), determine when the planet with be visible; chose nights when the moon is near new phase to increase sky darkness.
    2. Determine the relationship between the earth, sun and planet. Given your understanding of the motions of Venus and Jupiter, will Jupiter ever exhibit phases? Are there periods when Venus or Jupiter will not be visible at any time of the day?
    3. Try to observe the planet at least 4 times over a period of several days (superior planet such as Mars, Jupiter, or Saturn) or a week (inferior planets Mercury or Venus). How does the planet's position against the background sky change? How does the planet's appearance change?
    4. If you are observing Jupiter, plot the position of the four moons each time you observe. Can you identify one or more moons from observation to observation? What are the problems or challenges of making sure that a particular observation is of a particular moon?
    • Using a resource like Sky and Telescope, determine whether you can observe Jupiter or Venus at a reasonable hour. If observing either of these, try to do so on a dark night with no moon (while the moon is near New phase).


    • Describe how you determined which object to observe. How does the position of the object in the sky, the time of day it appears, and weather conditions affect your observing?
    • Describe your telescope or binoculars, and how you set them up to do your observations. What difficulties or challenges did you have to overcome? How did these affect your ability to make accurate observations?
    • Describe the object as you observed it. How do you observations support Copernicus' claim that the earth moves around the sun, or Galileo's claims that other planets move around the sun, and are made of "imperfect" substances?