Sun, Moon, and Stars: Astronomy for Beginners · Part I, Ch. X · Part 1: Part I: Our family in the sky, and its neighbors
12. Our neighbors' movements: the Pole-star and moving suns
Goal: Your child can find the Pole-star using the Pointers, explain why stars seem to circle it, and knows that the stars, and our Sun, really are moving.
You'll need
- The book, open to Part I, Chapter X
- An umbrella and some star stickers or chalk (to model the turning sky)
- A clear evening, a watch, and the Moon diary
What's in the book
The last chapter of Part I separates the stars' seeming movements (caused by the Earth's turning and journey) from their real ones. It shows how to find the Pole-star from the Pointers of the Great Bear, why stars near it never set, why the constellations never seem to change, and that our Sun is carrying its family toward the constellation Hercules.
The lesson, step by step
Read together
Read the chapter aloud. At the Pointers, draw the Great Bear (Big Dipper) together and draw a line from its two end stars to the Pole-star.
The umbrella sky
Put star stickers (or chalk dots) inside an open umbrella, including one at the very center for the Pole-star. Hold it over your child's head and turn it slowly.
SayThe center star stays put. The others go round it. Those near the edge dip below the 'horizon' (the umbrella's rim) and come back. That is how the sky seems to turn, because the Earth turns.
Ships on the horizon
Read the book's picture of the ships seen from a cliff.
In ten thousand years you might see something. In fifty thousand years you might see much.
SayThe stars race along, but they are so far away that in a person's whole life the patterns don't change.
We are moving too
Walk through a doorway or down a hall and watch the things at your sides slide backward. The book says astronomers used the same idea to find that our Sun is heading toward Hercules.
What we know now
The Pole-star is very close to, but not exactly at, the sky's north pole. Because the Earth's axis slowly wobbles, other stars take turns being the pole-star over about 26,000 years.
The 'distant centre' the book wonders about is the middle of our Milky Way galaxy. The Sun carries us round it at about 140 miles a second, once in about 230 million years.
Some of the star speeds in the book were measured again later. Sirius, for one, is actually drifting slowly toward us, not away.
Tell it back
Ask your child to explain why stars near the Pole-star never set, using the umbrella.
Check questions
Which two stars point to the Pole-star?
What would you see if you stood at the North Pole at night?
Toward which constellation is our Sun traveling?
Notice it this week
Find the Big Dipper and the Pole-star early one evening and sketch where the Dipper is. Two hours later, look and sketch again. It will have turned around the Pole-star.
If you live south of the equator, the Pole-star is below your horizon; use the Southern Cross instead, which circles the south pole of the sky.
Afterwards
Keep up the Moon diary. By now you may notice the Moon rises later each day.
Answers to the book's problems
The Pointers, the two end stars of the Great Bear (Big Dipper). The Pole-star straight overhead and all the stars circling round it once in twenty-four hours, never rising or setting. Hercules.
Worked out for this site from the scan. If a number in your copy differs, trust the book.