The top 10 reasons stars are interesting Hint: It’s not just heat & light!

1. OK, stars do give us heat & light We depend on liquid water for life (and after all, mammals emerged from the sea) If Earth were colder than 32⁰ F or warmer than 212⁰ F, we’d have no liquid water: energy from the Sun arriving at Earth keeps us at the right temperature for life

We depend on “daylight” to find food, and to try to avoid becoming someone else’s food We hide at night in part for the same reason Stuff that we eat (plants and animals) needs the same heat & light to exist We’ve evolved so that our eyes are “tuned” to the colors that our Sun emits!

2. Stars cook atoms essential for life! Only H, He, and Li are made when the Universe was born

After cooking, there’s even free home delivery of the new atoms to new generations of stars and planets Some stars gently puff off the new atoms into our Galaxy A few stars eject the new atoms violently

3. Some atoms were first discovered on our Sun, not on Earth! Census of all the atoms in the Universe: 90% hydrogen, 9% helium, 1% everything else

Helium, although #2 most common atom, was first discovered on our Sun! 1868: Pierre Jules Cesar Janssen, a Frenchman Not really that long ago: the first transcontinental railway was about the same time.

Why was helium so hard to find on the Earth?? Hint:

4. Stars don’t live forever, but the death of old stars helps trigger the birth of new stars!

5. Stars are rulers, scales, and calendars for the Universe We know the distance to our neighboring stars, the size of our Milky Way galaxy, the distance to other galaxies, and the size of the entire Universe due to tricks using stars as rulers We know how much stars weigh, and how many stars are in our Galaxy, due to tricks using stars as scales We know how long it has been since the beginning of the Universe (!!), using stars as calendars

6. Stars generate their energy using a green, non-polluting, incredibly cheap method that someday we will use on Earth Two hydrogen atoms are pressed together to make helium, simply because stars are really, really heavy! Some extra energy is released in the merger, and leaves the star as heat and light We’re trying to make this also work on Earth, but it’s hard! No luck yet.

7. In old age, stars can become very exotic objects

8. Stars can be used to test important laws of science that can never be verified on Earth Einstein’s Theory of General Relativity: how gravity works Existence of black holes and gravity waves Properties of tiny particles in the nucleus of atoms, e.g., neutrons Properties of mysterious debris from the nucleus, e.g., neutrinos

9. Stars are the first step in searching for intelligent life elsewhere in our Galaxy! There may be other living things in our own solar system, but probably not “intelligent“ If there is intelligent life elsewhere, it probably lives on planets like our own but around other stars Observations of stars have quite recently shown us that there are likely billions of other planets in our Galaxy Future observations of stars will help us select the best nearby candidates

10. Stars are Beautiful!