Unit D: The Atmosphere and Beyond

Which star is the only one that doesn't appear to change its position in the sky?

1. Get Set to Explore

Vocabulary

  • axis: An imaginary line that passes through Earth from the North Pole to the South Pole; Earth spins on its axis.
  • constellation: A group of stars that forms a pattern in the night sky.
  • horizon: The line where land and sky seem to meet.
  • rotate: To spin or turn.

Building Background

  • Review the vocabulary words and their definitions with the class.
  • Show the class a globe and ask volunteers to use the globe to show how Earth rotates on its axis. Review the cause of day and night.
  • Have students use a U.S. map to locate the two cities featured in the simulation: Boston, Massachusetts, and St. Augustine, Florida. Then have students locate where these cities would be on the globe. Explain that the simulation will show them what the night sky looks like from both of the cities on a particular day of the year. They will compare the position of some of the stars.
  • Review the appearance of these constellations: Ursa Major, which contains the Big Dipper; Ursa Minor, which contains the Little Dipper. To do this, you may wish to show the picture on Student Edition page D78 or other pictures of constellations in the night sky.
  • Write the Discover! question on the board. Encourage students to work in small groups to discuss how to figure out the answer. You may wish to give the hint that the answer is related to the movement of Earth. After three to five minutes, let students share their ideas with the class. Write them on the board to refer to later.

2. Guide the Exploration

  • Tell students to launch the Discover! Simulation and to listen closely to the introductory text and to the question. Guide students to realize that the stars appear to circle in the night sky because Earth is rotating on its axis. Let students revise their ideas on figuring out which star doesn't move in the night sky.
  • Direct students to choose a location, using the globe in the right corner of the screen, and to watch how the stars move in the night sky.
  • Encourage students to use the cursor to identify the Little Dipper in both locations and to watch the stars in this constellation carefully. The star at the end of the handle is the North Star, also called Polaris. It is the star that doesn't move in the night sky in the Northern Hemisphere.
  • When students finish viewing Step 2 of the simulation, ask them to identify the star that didn't move. The correct answer is the North Star, also called Polaris. Encourage students to explain how they figured out which star didn't move.

3. Review/Assess

  • Review Step 3's Wrap-Up text with the class. Reinforce the star that doesn't move is directly above the North Pole, which is aligned exactly with Earth's axis.
  • Introduce the Extension questions. If necessary, have students return to the simulation to verify that Polaris (the North Star) appears higher in the sky farther north, in Boston, than in St. Augustine, Florida.
  • Let students work in small groups to formulate answers. Guide them to understand that a person at the North Pole would be looking 90° straight up at Polaris. Because Earth is a sphere, the angle of the ground changes relative to Polaris; that is why Polaris appears lower in the sky as you go south. At the equator, the plane of the ground is parallel to Polaris, so the star can no longer be seen above the horizon.

If time permits, present children with the following questions:

  • Inquiry Skill Predict Imagine you were visiting Raleigh, North Carolina, which is about halfway between Boston and St. Augustine. Where would the North Star appear in Boston and St. Augustine? Answer: The North Star would appear lower in the sky in Raleigh than in Boston; it would appear higher in the sky in Raleigh than in St. Augustine.
  • Critical Thinking Synthesize No star is situated directly above the South Pole. Why would this have made navigating more difficult for sailors in the Southern Hemisphere? Answer: They wouldn't have had a pole star to tell them which way was due south; other stars would appear to move.

4. Reaching All Learners

On Level: Visual Learners

Encourage visual learners to make several sketches that show why the North Star does not appear to move in the sky. Their pictures should show the location of the North Star, the location of other stars relative to the North Star, and the Northern Hemisphere.