Activating Strategy
Describe how objects seem to move
across the sky [What can you observe?].
Why do objects seem to move across
the sky?
When instructed, share your response
with another student.
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.
Use your
notes to
record
important
information.
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?
All the motions and changes you
see are a result of 4 simple facts:
1. 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].
All the motions and changes you see are
a result of 4 simple facts:
3. 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 appear 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.)
Standing on the ground, we do
not perceive the motion of the
Earth, 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.
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.
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.
It happens slowly. From minute
to minute you do not 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 in the sky.
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.
Think of how you would see stars during the
earth’s rotation using the diagram below.
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
Time lapse videos
of stars
• http://www.classzone.com/books/earth_scie
nce/terc/content/visualizations/es0407/es04
07page01.cfm?chapter_no=visualization
• https://www.youtube.com/watch?feature=pl
ayer_embedded&v=pe4dpprVBGs
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
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: http://jimmie.squidoo.com/flip-book-fun
• Modeling the Night Sky [see resource page]
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.