Motion of the Stars

In Spring and Summer, when the Dipper is already overhead, advance diurnal motion only until the Dipper is aligned with the constellation outlines you have prepared, then go directly to “Versions of the Big Dipper.” Next return to this section, followed by the “Conclusion.” In Winter and Fall, follow the normal order: “Motion of the Stars,” followed by “Versions of the Big Dipper,” followed by the “Conclusion.” If you present the Dipper first, make appropriate minor changes in the following paragraphs.We have found each of the major constellations in tonight’s sky. 

If we kept watching tonight, would the stars remain like this? What would happen? Why?

Accept ideas from the audience.

Let’s find out by going through the entire night, sped up so that we will come to tomorrow morning in just a minute. Please keep track of your constellation to see what happens to it during the course of the night.

Also, please watch this star, which we said was Polaris.
What is special about its behavior?

Fade in music, gradually dim orange lights (or atmosphere and the Sun). 

DIGITAL EFFECT: Diurnal Forward
Run diurnal forward motion at a preset speed. If you have effects showing star trails, they can be used to illustrate how all the stars appear to revolve around Polaris.

Turn on NESW lights.
DIGITAL EFFECT: Star Trails 
If available on your system, make star trails to illustrate both diurnal motion and that all stars appear to revolve around Polaris. Also display the planetarium clock. Run diurnal motion continuously until you stop diurnal motion.

Stop diurnal motion at about 2 a.m.

It is now about two a.m.

Can you still see your constellation? What has happened to it?

What has happened to the Big Dipper?

What has happened to Polaris, the North Star?

Allow time for responses and discussion after each question. Encourage general observations such as “stars seem to rise and set like the sun,” or “the North Star always stays still.”

DIGITAL EFFECT: View Earth
This effect can be used as a finale. Lift off from Earth to view our home from space. Show the diurnal motion of Earth (allowing for discussion of night-side versus daytime-side of Earth and what that means). Next, stop diurnal motion and allow the presenter to orbit “back” around Earth to bring North America into view. When ready, stop orbiting and “land” back on Earth at our home coordinates and just before sunrise. Finally, run diurnal motion to see sunrise, marking the end of the show. A “shortcut” ending is to merely run diurnal motion from whatever time you are at to see sunrise.

We have observed that the stars seem to rise in the East and set in the West. Stars in the North turn around Polaris which appears to stand still. Even though it looks like the sky turns around the Earth, we have good evidence that the motion is caused by the Earth turning on its axis. Polaris does not appear to move because the Earth’s axis points towards it. 

The phrase “follow the drinking gourd” was remembered by freed or escaped slaves making their way north to safety via the “underground railroad.” Whether the “gourd” was the Big Dipper or the Little Dipper, the general direction (north) was correct for the desired purpose.

For any constellation, there is no “best” or “correct” story. Each of you can make up your own story about the Big Dipper and the other constellations. Stars belong to no one, so your own imagination is just as valid as the ancient Romans’ or anyone else’s.