Sun, Moon, and Stars: Astronomy for Beginners · Part III, Ch. III · Part 3: Part III: The stars
27. Different kinds of suns: variable, new and double stars
Goal: Your child can explain what variable stars, 'new' stars and double stars are, and can find a double star with their own eyes or binoculars.
You'll need
- The book, open to Part III, Chapter III
- Binoculars (optional)
- A flashlight and a ball (to show an eclipsing star)
- The star notebook
What's in the book
Stars are all different. The chapter describes variable stars (Mira in the Whale, Algol in Perseus, Betelgeuse, Delta Cephei), the 'temporary star' of 1572 that outshone Venus, real and seeming double stars (including the double-double near Vega), and the beautiful colored pairs seen in telescopes.
The lesson, step by step
Read together
Read the chapter aloud.
So some stars are large, some are small.
Make a 'winking' star
In a dark room, shine a flashlight toward your child from across the room. Slowly swing a ball across in front of it, again and again. The light dims each time the ball passes.
SayAlgol in Perseus does exactly this. A dimmer partner star passes in front of the bright one every few days.
Seeming doubles and real doubles
Read the book's two church towers. Say: Some double stars just happen to line up, one far behind the other. Others really go round each other, like Alpha Centauri.
What we know now
The temporary star of 1572 was a supernova: a whole star blowing itself apart. Smaller outbursts, called novae, happen when a tiny white dwarf star steals gas from a partner and flares up.
Stars like Delta Cephei brighten and dim in a steady beat, and the length of the beat tells how bright the star truly is. That let astronomers measure distances far beyond the reach of the book's base-line method.
Betelgeuse is a huge, restless red giant; in 2019 and 2020 it dimmed so much that people noticed it with their own eyes.
No star really shines green. Astronomers now think most of the greens and purples in colored pairs are tricks of the eye, caused by the contrast with a bright orange or yellow partner.
Find a double star
In the handle of the Big Dipper, the middle star has a faint close companion that sharp eyes can see on a dark night. In summer, use binoculars near bright Vega, as the book suggests: the little star beside it splits into two.
Tell it back
Ask your child to explain the difference between a variable star, a temporary (new) star and a double star.
Check questions
How long does Mira take to go through its changes?
What was special about the star of 1572?
Name the bright star in the Lyre the book mentions.
Afterwards
In the star notebook, draw the Big Dipper and mark the double star in its handle. Next clear night, check whether you can see both stars.
Tip
The faint star next to the Big Dipper's middle handle star is easiest to see when the Dipper is high in the sky, away from street lights.
Answers to the book's problems
About eleven months. It was so bright it could be seen at midday, outshining Venus, then slowly faded from white to yellow to red. Vega.
Worked out for this site from the scan. If a number in your copy differs, trust the book.