Sun, Moon, and Stars: Astronomy for Beginners · Part III, Ch. VII · Part 3: Part III: The stars
31. Further thoughts: new stars, air, and the lives of stars
Goal: Your child can tell what a nova is, why small worlds lose their air, and how today's picture of a star's life differs from the book's, and can look back over the whole course.
You'll need
- The book, open to Part III, Chapter VII
- The planet chart, the Moon diary and the star notebook from the whole course
- Paper and colored pencils for a 'life of a star' strip
What's in the book
The last chapter tells of a new star in Auriga in 1892, explains why small worlds lose their air while large ones keep it, and then guesses at the ages of heavenly bodies: the Moon very old, the Earth middle-aged, Jupiter younger, the Sun young and shining because it slowly shrinks. It closes with the author's reflections on faith.
The lesson, step by step
Read together
Read the chapter aloud. The last pages are the author's thoughts on God and creation; read them and talk about them in whatever way suits your family.
Why small worlds lose their air
Read the part about gas particles trying to escape. Say: Hot, light gas particles move fast. A big world's strong pull holds them in; a small world's weak pull lets them drift away. That is why the Moon has no air and the Earth keeps its oxygen and nitrogen.
The book is right about this, and about Earth losing its lightest gas, hydrogen.
The book's guess about the lives of stars
Read:
The sun is young still, in the very heyday of his existence.
The book imagines the Moon was once a tiny sun that burned out, and that the Sun shines because it slowly shrinks.
What we know now
The Sun shines by nuclear fusion in its core, squeezing hydrogen into helium. It is about 4.6 billion years old and about halfway through its life. In roughly five billion years it will swell into a red giant, then shrink to a small white dwarf.
The Earth is about 4.5 billion years old. The Moon was never a star; most scientists think it formed from the wreckage of a giant crash between the young Earth and another world.
Nova Aurigae was an outburst on a white dwarf star in a close pair, like those in Part III, Chapter III.
The universe itself is about 13.8 billion years old, and the light from its most distant galaxies has been traveling almost that long.
Draw the life of a star
Make a strip of five boxes: a cloud of gas (like the Orion Nebula), a young star switching on, a middle-aged yellow star like our Sun, a swollen red giant, and a small white dwarf.
Look back over the course
Lay out the planet chart, the Moon diary and the star notebook. Ask your child to pick their favorite thing they learned or saw, and to tell it to someone in the family.
Check questions
Why could the Moon not keep an atmosphere?
Which gas does the book say the Earth probably lost long ago?
When did Nova Aurigae first appear?
Afterwards
Keep looking up. Plan one more night outing: the next meteor shower, eclipse of the Moon, or a public night at a local astronomy club.
Answers to the book's problems
Because she is so small that her pull is too weak to hold the fast-moving gas particles. Hydrogen. On December 10, 1891.
Worked out for this site from the scan. If a number in your copy differs, trust the book.