1. 19.3 Stars

2. The Formation of Stars
Stars form out of clouds of hydrogen and helium and dust called nebulas.
As gravity pulls these elements together they began to heat up.
The heat fuels nuclear fusion reactions that create heavier elements, heat, and light.

4. Distances to Stars
Light Year – a distance that light travels in a vacuum in one year
9.5 trillion kilometers
The closest star to the sun is 4.3 light years away from the earth

5. Properties of Stars Color and Temperature
The color of a star indicates the temperature
Blue stars have a surface temp of 30,000 K
Blow torch
Yellow stars have a surface temp of 6000 K
A flame
Red stars have a surface temp of 3000K
Cooling embers in a fire

7. Properties of Stars Brightness Size and Mass Composition
Most stars are like the sun and are made up of mostly hydrogen and helium

8. H-R Diagrams
A diagram used to estimate the sizes of stars and their distances
Used to infer how stars change over time
Compares surface temperature and absolute brightness
The mass of the star places it in the proper place in the main sequence

10. Life Cycle of a Star

12. Death of a Star
As nuclear fuel in the core of the star begins to run out, the star begins to become hollow.
Nuclear reactions outside the core cause the star to expand and then eventually collapse.
After this collapse, a star can become a white dwarf, neutron star, or a black hole.

13. Galaxies
Galaxy – a huge group (billions) of individual stars, star systems, star clusters, dust, and gas bound together by gravity.
There are billions of galaxies in the universe

14. Galaxy Shapes
Spiral – a bulge of stars at the middle with arms extending outward like a pinwheel
Barred-Spiral Galaxies – a spiral galaxy with a bar through the center and the arms are extending from the bar
Elliptical Galaxies – are spherical or oval shaped
Irregular Galaxies – have a disorganized appearance.

15. Spiral

16. Barred-Spiral

17. Elliptical

18. Irregular

19. The Milky Way The Milky Way is a Spiral Galaxy
100 billion stars and a diameter of over 100,000 light years
Young stars are at the center of the milky way.
The location of our solar system