Chapter 30.1

1. Chapter 30.1 Characteristics of the stars

2. What is a star? • Stars give off a tremendous amount of electromagnetic energy • This type of energy comes from nuclear fusion • Nuclear Fusion- the combination of light atomic nuclei to form heavier atomic nuclei Characteristics of Stars

3. Analyzing star light • Astronomers learn about stars by analyzing the light that stars emit • Spectrographs • Starlight passes through and produces a display of colors and lines called a spectrum Characteristics of Stars

4. Types of Spectra • Emission or bright-line • Absorption or dark-line • All stars have • The dark-line spectra reveals the star’s composition and temperature • Continuous Characteristics of Stars

5. The composition of stars • Stars are made up of different elements in a gaseous form • Colors and lines that are emitted from star indicate what elements make up that star • Inner layers of a star are hotter than outer layers Characteristics of Stars

6. The Composition of Stars • A star’s most common element is Hydrogen followed by Helium • Stars are also made up of carbon, oxygen, and nitrogen but usually in small quantities adding up to about 1% of a stars mass Characteristics of Stars

7. Temperature of a star • Indicated by it’s color • Most star temperatures range from 2800 ºC to 24,000 ºC although some may be hotter • Generally blue stars are the hottest and Red stars are the coolest • Yellow stars, such as the sun, have a surface temperature of ~5,500 ºC Characteristics of Stars

8. The size and mass of stars • The smallest stars are slightly bigger than Jupiter 1/17 of our sun’s size • The sun’s diameter is about 1,390,000km – the sun is considered a medium sized star • Many stars have about the same mass as the Sun • Stars that are very dense have more mass than the sun • Stars that are less dense have a larger diameter but still have less mass Characteristics of Stars

9. Stellar Motion • 2 types of motion are associated with stars • Actual motion through space • Apparent motion across the night sky Characteristics of Stars

10. Apparent Motion of Stars • Apparent Motion is caused by the movement of the earth • Stars seem to move in a counter clockwise motion around a central star called Polaris • Polaris does not appear to move much Characteristics of Stars

11. Apparent Motion of Stars • Earth’s revolution around the sun causes the stars to appear to move in a 2nd way • Different stars become visible during different seasons • Visible stars appear slightly to the west • Stars appear to move a small distance nightly Characteristics of Stars

12. Circumpolar Stars • Some stars are always visible in the sky at night these stars never pass below the horizon during their nightly or annual movement • They appear to circle the North Star Characteristics of Stars

13. Circumpolar Stars • The stars of the little dipper are circumpolar stars • The further an observer is from the North Pole the less circumpolar stars they see Characteristics of Stars

14. Actual Motion of Stars • Most stars have several types of actual motion • They move across the sky • The revolve around another star • They either move away from or toward our solar system Characteristics of stars

15. Actual Motion of Stars • The stars spectrum allows astronomers to learn about how a star is moving in space • Doppler Effect- an observed change in the frequency of a wave when the source or observer is moving • Blue and red shifts Characteristics of Stars

16. Distances to Star • The distance between Earth and the stars are measured in what? • The speed of light is 300,000 km/s • Light travels ~9.46 trillion km in 1 year Characteristics of Stars

17. Light From Stars left at some point in the past • Light from the sun takes about 8 minutes to reach Earth • The closest star is Proxima Centauri-which is 4.2 light years from Earth • 300,000 times the distance from Earth Characteristics of Stars

18. Relatively close stars distance is determined by measuring parallax • Observers can examine different stars due to the fact that Earth orbits the sun • This allows observers to study different perspectives of a star Characteristics of Stars

19. Stellar Evolution Chapter 30.2

20. Hertzsprung-Russell Diagram H-R Diagram Stellar Evolution

21. Stellar Evolution • Main sequence- the location on the H-R diagram where most stars lie; it has a diagonal pattern from the lower right to the upper left • Stars with in this band are called main-sequence stars or dwarfs • The sun is a main-sequence star Stellar Evolution

22. Star Formation • Stars begin in a nebula • A cloud of gas and dust • Consist of ~70% hydrogen 28% helium and 2% heavier elements Stellar Evolution

23. Star Formation • Newton’s law of universal gravitation- all objects in the universe attract each other with a force that increases as the mass of any object increases of the distance between the objects decreases Stellar Evolution

24. Star Formation • Protostars • a cloud of interstellar gas and dust that gradually collapses, forming a hot dense core, and evolves into a star once nuclear fusion can occur in the core Stellar Evolution

25. Star Formation • Gravitational energy is converted to heat energy as more matter is pulled into a protostar • Plasma Stellar Evolution

26. The Birth of a Star • The temperature continues to increases to ~10,000,000 degrees Celsius • This increase in temperature causes nuclear fusion to begin- once nuclear fusion begins in a star the process can continue for years Stellar Evolution

27. The main-sequence stage • 2nd stage and the longest stage in the life of a star • Energy continues to generate in the core of the star as hydrogen fuses into helium • Stars with about the same mass as the sun will stay on the main sequence for about 10 billion years Stellar Evolution

28. Leaving the Main-Sequence • 3rd stage • This stage is entered when 20% of the hydrogen atoms in the core have fused into helium • The outer shell of the star will expand greatly during this stage Stellar Evolution

29. Leaving the Main Sequence • When a star’s shell gases becomes cooler it expands and the glow of the star will become reddish • These stars are known as giants because they are larger than stars with the same surface temperature • Giant Stars-a very large and bright star whose hot core has used most of its hydrogen Stellar Evolution

30. Giant Stars • Giant stars such as Arcturus are 10 times larger than the sun • Most stars that have the same mass as the sun will become giant stars • Eventually they will move off the main sequence on the H-R diagram Stellar Evolution

31. Super giants • Stars that are already larger than the sun will become super giants when they enter into their 3rd stage • Ex. Betelgeuse 1000 times larger than the sun • These stars only make up a small amount of the stars in the sky • Their surface temperatures are relatively cool Stellar Evolution

32. The final Stages of a Sun-like Star • When energy is no longer available from fusion a star enters it final stages • Planetary nebulas- a cloud of gas that forms around a sun-like star that is dying • Some form a sphere of ring around the star however many planetary nebulas form more complex shapes Stellar Evolution

33. White Dwarfs • White dwarfs shine for billions of years before they cool completely • White dwarfs are in the lower left of the H-R diagram • They are hot but dim • These stars are very small • The more they cool the more fainter they become Stellar Evolution

34. Novas and Supernovas • Novas may cause a star to become a lot brighter than it normally is, this brightness will fade within days and it will return to its normal brightness Stellar Evolution

35. Supernovas -a star that has such a tremendous explosion that it blows itself apart • Supernovas are more violent than novas • The explosion completely destroys the white dwarf and may destroy much of the red giant Stellar Evolution

36. The Final Stages of Massive Stars • Supernovas in Massive stars • Small percentage of white dwarfs become supernovas • Massive stars become supernovas as part of their life cycles • Fusion in these stars will continue until the core is almost entirely made of iron • The core will begin to collapse because of its own gravity Stellar Evolution

37. Supernovas in Massive Stars • Energy is released as the core collapses and is transferred to the outer layers of the star • Eventually the star will explode outward Stellar Evolution

38. Neutron Stars • A star that has collapsed under gravity to the point that the electrons and protons have smashed together to from neutrons • Neutron stars rotate rapidly Stellar Evolution

39. Pulsars • A rapidly spinning neutron star that emits pulses of radio and optical energy • Each pulse we detect tells us the the star has rotated • Newly formed pulsars are surrounded by remnants of supernovas Stellar Evolution

40. Black Holes • An object to massive and dense that even light cannot escape its gravity • They are difficult to locate because they do not give off light • But they can be observed by the effects it may have on a companion star • Matter from a companion star is pulled into the black hole Stellar Evolution