1. Essential Question: Why do objects seem to move across the sky?
Standard S6E1d. Explain the motion of objects in the day/night sky in terms of relative position.

2. Activating Strategy
Describe how objects seem to move across the sky [What can you observe?]. Answer the Essential Question to the best of your ability. Why do objects seem to move across the sky? When instructed, share your response with another student.

3. Movement of Objects in the Sky
The sun, the stars, the moon and other planets all appear to move across the sky.
In which direction do they seem to move?
The sun, the stars, the moon and other planets appear to rise in the East and set in the West.
But why?

4. All the motions and changes you see are a result of 4 simple facts:
The Earth is spinning on its axis [one turn every 24 hours].
2. The Moon is orbiting around the Earth [one orbit every 27.3 days].

5. All the motions and changes you see are a result of 4 simple facts:
The Earth and all the other planets are orbiting the Sun, all in the same direction, and all in roughly the same plane (i.e. it's like they are all laid out on a large dinner plate with the Sun at the center). The outer planets orbit more slowly than the inner planets.
4. The stars are stationary. (They do, in fact, move very quickly. But they are so far away that the motion appears to us to be too slow to perceive without special instruments.)

6. Standing on the ground, we do not perceive the motion of the Earth, either its rotation or its orbit around the Sun -- instead, it seems to us as though we are stationary and the sky is moving around us.

7. Here is an example of how the rotation of the Earth makes the Sun appear to move across the sky: If an object is at a fixed location on a wall (for example, a clock) and you are facing it, then you can see the clock. If you rotate so that you’re facing away from the clock, you can no longer see it. While you are rotating, the clock will, from your point of view, appear to be moving.

8. Like the sun, if you pick out a star in the sky, it will appear to make an arc across the sky. This is because, for our purposes, we can consider the star to be fixed in space, and the Earth is rotating underneath it.

9. This happens slowly, so from minute to minute you don't notice the star's motion. However, over the course of a few hours you will be able to tell that the stars have moved a substantial distance on the sky. Since, like the Sun, the stars will (for the most part) appear to rise in the east and set in the west. The images to the right are time exposure photos taken of the same stars over the same spot.

10. Think of how you would see stars during the earth’s rotation using the diagram below.

11. When the Sun appears during the day in the Summer, the winter constellations are obscured by the sunlight bathing our atmosphere, and when night falls, the summer constellations are visible. Conversely, the summer constellations are obscured by the Sun during days in Winter, while the winter constellations are visible at night

12. Time lapse videos of stars

13. The North Star appears to remain stationary in the sky. Why
The North Star appears to remain stationary in the sky. Why? The North Star lies almost perfectly above the Earth's rotational axis
North Star

14. Possible Activities
Students can draw a diagram illustrating what causes objects to appear to move across the sky [box on notes for illustration]
Students can make a flipbook illustrating objects seeming to move across the sky (be sure they include the cause of the appeared movement). The following website provides information on making a flipbook:

15. Summarizing Strategy: 3-2-1
Identify 3 objects that appear to move across the sky.
Identify 2 interesting facts from today’s lesson.
Identify the main reason objects appear to move across the sky.