Stars and the Sun

1. Stars and the Sun BC Science Probe 9 Section 13.3-13.4 Pages 425-436

2. Stars • Stars have a life cycle. • Beginning (birth) • Midlife • End (death) • The Sun, which is the star closest to us, has been around for 5 billion years and is expected to last another 5 billion years.

4. Stellar Birth • Stars are born when nebulas collapse on themselves. • Small amounts of matter collide and stick together making bigger masses that have more gravity.

6. Stellar Birth • When the nebula begins to collapse, the region with the greatest density will pull more of the hydrogen gas toward it than the rest and will begin to grow. • This is called a protostar.

7. Stellar Birth • Once the protostar gains enough mass and gets dense enough, that material in the centre will become hot enough to start nuclear fusion!

8. Nuclear Fusion • This happens in the core of the star. • Hydrogen nuclei fuse together to form helium nuclei. • 6 hydrogen protons fuse to produce 1 helium nucleus with 2 protons and 2 neutrons as well as 2 free protons and a ridiculous amount of energy! • The energy can be in the form of heat, light, x-rays, gamma rays and particles.

9. Nuclear Fusion

10. Nuclear Fusion • The energy of the nuclear fusion causes thermal expansion. • The force of the expansion counters and balances the gravity to stop the collapse. • Our Sun went through this process. It probably took 30 million years to condense and ignite.

11. Stellar Midlife • The fusing of hydrogen to helium continues just like what is happening in the Sun right now. • The energy that is released can take thousands of years to reach the outer layers of the Sun where it is released as light.

13. Solar Anatomy • The part of the Sun that produces the energy is the core. • Temp. - 1.5 x 107 ⁰C • Radius – 1.75 x 105 km

14. Solar Anatomy • The next layer of the Sun is the radiative zone. • 3.5 x 105 km thick

15. Solar Anatomy • The outer layers of the Sun are the convective zone and the photosphere. • Convective zone • 2 x 105 km thick • 2 x 106 ⁰C • Photosphere – the visible part of the Sun • 300 km thick • 5500 ⁰C

16. Solar Anatomy • The layers all rotate at different speeds and once the energy reaches the convective zone, it moves by convection currents to the surface.

17. Solar Anatomy • Outside of the photosphere are the chromosphere and the corona. • Chromosphere • Layer of gases at 60 000 ⁰C • Corona • Layer of gases at 2 x 106 ⁰C

18. The Sun’s Surface • The surface of the Sun is not smooth and featureless. • It looks more like the surface of a boiling liquid.

19. The Sun’s Surface • Sunspots • Dark spots on the surface of the Sun. • The vary in size and regularity. • Caused by disturbances in the Sun’s magnetic field. • They appear in pairs with opposite magnetic poles which disturb the magnetic field more. • The magnetic disturbances caused by sunspots can lead to solar flares and solar prominences.

22. The Sun’s Surface • Solar prominences • 1 x 1011 tonnes of glowing hydrogen released from the photosphere. • Last 4-5 minutes

24. The Sun’s Surface • Solar flares • Ejection of large quantities of gas and charged particles. • Last a very short time

25. The Sun’s Surface • Solar wind • This is happening all the time. • Ionized gas emitted from the Sun. • Stronger when there are flares and prominences. • Creates aurora borealis. • Disrupts communications equipment and other electronic systems.