Stars and the Sun

1. Stars and the Sun Chapter 18.2

2. Objectives • Describe the basic structure and properties of stars • Explain how the composition and surface temperatures of stars are measured • Recognize that all normal stars are powered by fusion reactions that form elements • Discuss the evolution of stars

3. Vocabulary • Constellation • Red star • White dwarf • Supergiant • Supernova • Neutron star • Black hole

4. Our sun is a Typical Star

5. Objective 1: The Structure of the Sun • Stars are huge balls of mostly hydrogen and helium • Held together by gravity • Inside the core there is enormous pressure • Stars are driven by Fusion

6. Fusion • Hydrogen is fused into helium, which releases energy

7. The sun’s external temperature • 5500 Celcius • Gives off WHITE light • It appears yellow in our sky because our atmosphere scatters the violet and blue light, leaving yellow • The scattered light gives us our blue sky • When the sun is low, at sunset, more blue is scattered and the sun can look orange

8. Heavy Metals • Our solar system contains many heavy metals • Since these form when stars explode – our solar system must have been formed from the star dust of exploding stars

9. 1 Core 2 Radiative zone 3 Convective zone 4 Photosphere 5 Chromosphere 6 Corona 7 Sunspot 8 Granules 9 Prominence

10. The Core • The sun is Plasma not gas • Where most Fusion takes place • All of the sun’s energy comes from the core

11. Radiation and Convection Zones • Remember how heat moves? • Radiation the energy is absorbed and re radiated out from the next particles • In the Radiation zone – Energy moves slowly • Between the Radiation zone and the Convection zone is the Tachocline • a shear zone, the convection zone has fast moving currents • may be responsible for the formation of the magnetic field

12. Convection Zone • In Convection there are currents that help the energy flow outward • Each current flows heat up, cools and sinks back down • Forms magnetic regions all over the sun • The Granules are visible turbulence from these flows • It takes 10,000 to 170,000 years for energy to travel from the core to the surface (scientific estimates)

13. Photosphere • The visible surface of the sun • Temperature at the surface is 6000 Celcius • It is not as dense as air on earth

14. Everything above the photosphere is the atmosphere of the sun There are 5 zones • Temperature minimum • Chromosphere • Transition • Corona • heliosphere

15. Temperature Minimum • Coolest place in the sun is between the Photosphere and the Chromosphere • 4000 Celcius • It is unknown why it is cooler

16. Chromosphere • Named from the visible colors • Appears as a bright flash before an eclipse • Temperature increases to20,000 C

17. Transition • Below transition gravity forms sun • Above transition gravity is less dominant • Temperature rises – Helium is ionized and holds heat

18. Corona • During a solar eclipse, the corona can be seen with the naked eye

19. Corona • Can extend past earth • Temperatures can reach 1 to 3 million Celcius • Scientists don’t know why • One reason may be magnetic reconnection – a process that releases energy stored in magnetic fields

20. Heliosphere • Extends thru the solar system • Includes the solar wind and the suns magnetic field • In 2004 the Voyager space probe encountered a shock wave believed to be part of the heliosphere, it was 50 AU away from the sun

22. Sunspots • Areas of the sun that appear darker because they are cooler • They are cooler because they have strong magnetic fields – magnetic fields decrease surrounding pressure and don’t let hot gases flow • Most sunspots are the size of the earth • Can be seen with filters

23. Effect of sun spots on earth • More sun spots – correlate to higher earth temperatures • Fewer sunspots – cooler temperatures • In 1645-1715 sunspots disappeared and there was a mini ice age • Sunspots increase activity of Northern Lights

24. Solar Cycle • Sunspots increase and decrease every 11 years • Last peak May 2000 • We are heading back into a peak of sunspot activity in 2011 – It’s time to take a trip to Alaska!

26. Granules • It’s kind of like looking at the surface of a boiling pot of spaghetti sauce – the bubbling • Top of convection columns in the sun, they surface in the photosphere

27. Prominence and solar flares

28. What’s the difference • A prominence is something sticking out – they are often shaped like loops • They follow the magnetic field lines • Can be stable for days or months • Solar Flares are explosions under the surface of the sun – the blow clouds of gas out into space • Much larger events

29. Prominance • Sun quake caused by solar flare

30. Looking at the sun • Brief periods don’t cause damage – more likely to for young people or at high elevation • UV Exposure believed to contribute to Cataracts (not from looking directly at sun) • Looking thru binoculars can damage eyes (concentrated) • Looking at Partial eclipses without filters is dangerous – the eye’s pupil doesn’t contract as much as it should

31. Objective 2: Explain how composition and surface temperatures of stars are measured • Otherwise known as how do we know all this? • Cameras, telescopes, filters to detect… • visible light, radio waves, electromagnetic radiation… • Spectroscopy • Can determine temperature, age, rotation, magnetic field and movement towards or away from us

32. Spectroscopy • Study light • Split light into wavelengths • Each element has a spectral pattern it’s like a fingerprint for Hydrogen and Helium • The red shift that shows us the Universe is expanding is seen because the fingerprint isn’t exactly where it is supposed to be

33. Young Stars contain more elements • Stars are mostly hydrogen and helium • Each element contains a spectral pattern • Our Sun is middle aged

34. Temperature seen with color • Again – we look at the spectral patterns • Blue suns are hotter – 220,000 C • Red suns are cooler – 17,600 C • Our Yellow sun – 55,000 C

35. Rotation • Rotation is seen in smudges in the spectral pattern

36. Redshift The boxes show redshifted Galaxies

37. Where are they in time?

38. Objective 3: Fusion • The core of stars is extremely hot and dense – gravity squishes it together • In these conditions - Stars convert hydrogen to helium • As stars age, the run out of hydrogen and begin making carbon, oxygen, nitrogen… • Older stars can produce elements as heavy as lead

39. Objective 4: Evolution of Stars • Stars are born from massive gas clouds that coalesce from gravity • When the pressure and temperature get high enough – fusion starts and the star starts to shine

40. How long will our sun live?

41. What happens when the hydrogen runs out? • When stars run out of hydrogen, the core collapses while the outer edge expands (it cools) • The collapse lets the sun start fusing helium into heavier elements • When our sun becomes a red giant it will swallow up earth – it’s diameter will reach mars

42. Planetary Nebula • When the red giant has nothing left to fuse it releases the outer layers into space • What’s left becomes a White Dwarf • White Dwarfs are as small as a planet but very dense • They eventually Burn out

43. What happens to bigger stars? Up to 40 times our sun Even Bigger You get the same supernova The final collapse creates a Black Hole • When the star burns it’s hydrogen it collapses very quickly • Produces a shock wave and very bright light • A Supernova • The final collapse of a supernova creates a Neutron Star

44. Supernova Explosion

45. What path will our sun take?What path will other stars take?

46. Interaction of White Dwarf and Black Hole • This is a computer simulation – scientists would like to find this happening out there

47. What happens after stars die? • New stars form from Stardust • We are stardust • (better described as NUCLEAR WASTE)