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Name________________________ Date___________ Hour _____ H-R DIAGRAM Stars live and die on such a long time scale that humans often have a problem understanding that a star is a like giant factory that is driven by gravity to fuse light elements like hydrogen under heat and pressure into heavier atoms like helium and the other heavier elements of the periodic table. At the cores of stars, hydrogen atoms are squished together under extreme heat and pressure to fuse together to make larger atoms. In the process a small amount of matter is converted into large amounts of radiation energy. (E=mc2) This radiation energy travels out from the core of the star into space. A billionth of the sun’s radiation energy, (the sun is round and gives off energy in all directions) travels to earth, passes through its five layered atmosphere and is absorbed by the chlorophyll in plant leaves. Chlorophyll in the leaves combines carbon dioxide and water to store the radiation energy as chemical bonds in a sugar molecule. If the plant is buried under water and decays for millions of years under heat and pressure, the oxygen atoms found in the sugar molecules are cooked off and only the hydrocarbons remain to form the fossil fuels of coal, oil and if it is heated even more, natural gas. The Hertzsprung - Russell diagram Enjar Hertzsprung and Henry Russell were working on the same problem on different sides of the Atlantic Ocean at the same time. Each took the known brightness and temperatures of stars cataloged by Anne Cannon and plotted them to a graph sheet. Three quarters of a million stars were plotted to see if there were patterns. Four main groups were discovered: “Super Giants”, “Giants”, “Main Sequence” and “White Dwarfs”. Stars on the main sequence generate energy by converting (via fusion) hydrogen into helium. As stars use up their hydrogen fuel, they evolve off the main sequence into the giant or supergiant phase. A star will move from left to right -- from hot to cool -- as it ages. When astronomers actually measure stars in the sky and plot them on the HR diagram, they find about 90% on the main sequence, (Most main sequence stars are red dwarfs) about 10% in the giant area on the right, and very few in the area between. DIRECTIONS: 1. Using the graph “paper” supplied in this lab, plot the 30 stars listed in Data Tables 1 & 2. 2. Use one colored pencil to plot the temperature and brightness data for each of the 15 nearest stars. Make a small dot of the same color for each of the stars listed and give each dot its appropriate ID number. 3. Using a different color pencil, plot the temperature and brightness for each of the 15 brightest stars. Again, use the same color for ALL the dots and label each with its ID number. 1 How does our sun compare to other stars? Data Table 1 15 Stars nearest Earth in the color__________ ID# 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. Star Sun Proxima Centuri Alpha Centuri A Alpha Centuri B Barnard’s Star Wolf 359 Lalande 21185 Sirius A Sirius B Luyten 726-8A Luyten 726-8B Ross 154 Ross 248 Epsilon Eridani Ross 128 Temperature (°C) 5600 5800 4200 2800 2700 2600 13200 13000 10700 2700 12700 12000 2700 4500 2800 Brightness (Sun = +2) +2 +2.5 -2 -5.5 -6 -7 -13.5 +4 +12 -11.5 -12 -12 -4 -3 -9 Distance from Earth in Light Years 0.000 02 4.3 4.3 4.3 5.9 7.6 8.1 8.8 8.7 8.9 8.9 9.4 10.3 10.7 10.8 Data Table 2 15 Brightest Stars in Northern Hemisphere in the color________ ID# Star 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29. 30. Aldebaran Altair Antares Arcturus Betelgeuse Capella Deneb Fomalhaut Pollux Procyon Regulus Rigel Sirius Spica Vega Temperature (°C) 4200 6000 3400 4500 16200 5900 9900 13000 4900 8500 20000 11880 18000 21000 17700 Brightness (Sun = +2) +9 +8 +7 +8 +14 +13 +14 +13 +8 +2 +9 +4 +6 +8 +5 Distance from the Earth in light years 68 16 424 36 587 42 1630 23 35 11 84 800 8.8 260 26 2 TEMPERATURE VS. BRIGHTNESS OF 30 SELECTED STARS The O B A F G K M at the top of the page can be remembered in order with the mnemonic sentence- Oh Be A Fine Girl (or guy), Kiss Me. In short, the hottest stars are O class stars and the coolest, yet are still undergoing fusion, stars are M class stars. The letter label applies to all stars to the right of the letter to the next letter. The second half of the star classification is how bright a star is. These numbers show the brightness of a star in comparison to our sun. Observe your graph. Can you place the stars in four distinct groupings? Please draw a circle around the four groups and label each group as Super Giants, Giants, Main Sequence, or White Dwarf, as you feel the name best applies. Use your graphs to answer #1-5. Open the following links and click on the two pictures and use the information to answer the five questions that follow. http://aspire.cosmic-ray.org/labs/star_life/hr_interactive.html http://astrosun2.astro.cornell.edu/academics/courses//astro201/sun_hrtrack.htm Sun’s path on HR diagram 3 1. Explain the Hertzsprung-Russell (H-R) diagram. The H-R Diagram compares stars brightness to its temperature into four groups, with most stars falling into the main sequence followed by the grouping of giants, super giants and white ______________________. 2. Explain how you can infer the temperature, life span, and mass of a star from its color. A star’s color tells you its _______________, from that and its size you can infer its place in the life cycle of a star. 3. Use the H-R diagram to explain the life cycles of stars. H-R diagrams illustrates how a star is born from a hydrogen nebula, becomes a main sequence star and then a supergiant or giant finally dying as a black dwarf, neutron star or pulsar or ___________ hole 4. Explain the balance between fusion and gravity in a star (equilibrium). A star’s is made from hydrogen that is squished together to form helium in the cores of stars by gravity causing heat and ________________________. 5. Compare the evolution paths of low-, moderate-, and high-mass (1, 10 & 40 mass) stars using the H-R diagram. 1m*- A low mass star will live billions or trillions of years and spend most of its life on the main sequence. 10m*- A medium mass star will live for about 10 million years, and then swell into a red giant and then die as _____________________________ star or pulsar. 40m*- A high mass star only lives for millions of years, then swells into a giant or super giant and then makes heavy elements out of light elements, and dies as a supernova that make black _________________ 4 Extra challenge! 6. What color is Polaris? ________________________________________________________ 7. What temperature is Rigel? ____________________________________________________ 8. How bright (luminous) is Sirius? ________________________________________________ 9. List three stars on the Main Sequence: ____________________________________________ 10. How is Alpha Centauri different from the Sun? ____________________________________ 11. Is Procyon B an old star or a young star? _________________________________________ 12. As luminosity increases on the Main Sequence, the temperature of the stars _____________. 13. Which stage of life is the Sun currently in? ________________________________________ 14. What is the largest named star on the chart? _______________________________________ 15. As star color changes from red to white to blue, star temperature _______________________ 16. What color are the small stars on the Main Sequence? _______________________________ 17. What is the name of the brightest white dwarf? ____________________________________ 18. Name two supergiants: ________________________________________________________ 5 This is a picture of some of the stars you graphed. Are your star ID numbers in about the right place? Think of this as a partial answer key! If the original star is very massive, (10 times the mass of the Sun) the collapse will be extremely rapid and the release of energy so great the star explodes. Its outer parts, now rich in heavy elements, will be blown far out into interstellar space, where they will be visible as a supernova remnant. After 100,000 years or so the debris will have mingled with the interstellar gas, enriching it with heavy elements. From this gas a new generation of stars will be born. FYI: More information http://www.astro.ubc.ca/~scharein/a311/Sim/hr/HR diagram.html HR Diagram Simulator Australia Telescope Outreach and Education - Stellar Evolution Links http://outreach.atnf.csiro.au/education/senior/astrophysics/stellarevolution_links.html Mathtools.net-some models: http://www.mathtools.net/Java/Astronomy/ NASA students 5-8: http://www.nasa.gov/audience/forstudents/5-8/index.html http://www.enchantedlearning.com/subjects/astronomy/stars/startypes.shtml http://81science.com/81Science.com/History_of_the_Universe.html Phases of the inner planets (interactive Java animation) Retrograde motion (interactive Java animation) Kepler's Laws (interactive Java animation) Cratering (Java applet) 6