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Introduction to Stars

Introduction to Stars. Our Sun is a star and its closeness to Earth has allowed astronomers to study and analyze its properties and characteristics and apply this knowledge to the study of other stars. What are a stars characteristics?. Stars differ in… Mass Size Temperature Color

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Introduction to Stars

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  1. Introduction to Stars • Our Sun is a star and its closeness to Earth has allowed astronomers to study and analyze its properties and characteristics and apply this knowledge to the study of other stars.

  2. What are a stars characteristics? Stars differ in… • Mass • Size • Temperature • Color • Luminosity

  3. Mass and Composition of Stars • Mass and composition determines most of the properties of a star. • The more massive a star is, the greater the gravity, the hotter and denser a star must be.

  4. Composition • Through spectroscopy, the dark lines in the spectra show scientists what elements are present in the gases of stars. • Hydrogen and helium and smaller amounts of other elements are found in stars.

  5. Star Size • The diameters of stars range from as little as .1 the sun’s diameter to hundreds of times larger. • The mass of stars can be from less than .01 to 20 or more times that of our sun. Extremely rare are stars that are over 50 times the Sun’s mass. • Our Sun is a medium sized star.

  6. Star Energy • The enormous pressure and heat in a star’s core convert matter into energy. • Stars consist of controlled atomic reactions called nuclear fusion in which hydrogen (nuclei) atoms fuse to form helium (nuclei) atoms. • During each step of the process, mass is lost and energy is released.

  7. Star Energy cont. • The energy released causes the star (Sun) to shine and gives the star its high temperature. • Stars like our sun can change 600 million tons of hydrogen into helium every second! • Star stability – this energy stabilizes a star by producing the pressure needed to counteract gravity.

  8. Star Energy cont. • If a star’s temperature is hot enough, carbon can react with helium to form oxygen, then neon, then magnesium, and then silicon. • Other types of reactions can produce even heavier elements which we learn about later in the life cycle of a star.

  9. Temperature of stars • Stars in the sky show tinges of different colors which reveal the star’s temperatures. • Blue stars shine with the hottest temperatures and red stars shine with the coolest • Our Sun is a yellow star having a surface temperature of about 5,500ºC

  10. Temperature of Stars • The cooler red stars have longer wavelengths and may be only detected with infrared telescopes • The hot blue stars have shorter wavelengths may be detected with ultraviolet or x-ray telescopes

  11. Spectral Type Classification • Stars are classified according to their patterns of absorption lines in its spectrum. • Astronomers place stars in spectral (color) class categories based upon their surface temperature. • The classes also correspond to stellar temperatures (O stars are the hottest and M stars are the coolest) see chart • When you look into the night sky the stars appear to be white in color but in reality their colors can be red, orange, and even blue! Betelgeuse is red, Sirius is white and our Sun is yellow!

  12. Classification of Stars

  13. The Spectral Class is OBAFGKM or Oh Be a Fine Guy/Girl Kiss Me • From Hottest to Coolest: Violet, Indigo, Blue, White, Yellow, Orange, Red • O or violet is the hottest (>25,000oC) and • M or red is the coolest (3,500-2,000oC)

  14. Stellar brightness • The visibility of a star depends on its brightness. • Absolute magnitude – the true brightness of a star if all stars were at a uniform distance from Earth. • Apparent magnitude – the brightness of an object as we see it from Earth with the naked eye. • The brighter a star actually is, the lower its absolute magnitude (and the lower the numerical value). • On our diagram, we use the Sun to compare Absolute Magnitude to other stars.

  15. Luminosity • The energy output from the surface of a star per second measured in watts. • How bright a star is relative to the Sun • The brightness of a star depends upon the distance and its luminosity. Think it over • The star Rigel in Orion is about 60,000 times larger than our sun. • Why does our sun appear brighter than Rigel?

  16. The H-R Diagram • The properties of a star are closely related and can be demonstrated on a graph called the Hertzsprung - Russell diagram (H-R diagram) • About 90 % of stars including the Sun fall along a broad strip of the H-R diagram called the main sequence. Included in the diagram will be:

  17. The H-R Diagram cont. • Temperature is noted in ºC • Upper left hand corner – hot, luminous stars • Lower right corner – cool, dim stars • Star size and color • Spectral Classification noted also because of its temperature relationship

  18. H-R Diagram cont. • Absolute magnitude is in comparison to the Sun ( 1 being the Sun’s AM ) and multiplied either ( X a whole number) for an amount greater than or (X a decimal number) for an amount less than the AM of the Sun. • Apparent Magnitude the brightness of an object as it appears from Earth with the naked eye • Stars that are part of the main sequence indicate that all these stars have similar internal structures and functions.

  19. Stars are grouped into types by temperature and luminosity

  20. Upper left stars are Large,Hot,Luminous Blue Giants Lower right stars are Small, Cool, Dim Red Dwarfs #1. Main Sequence Stars, • 90% of stars • A middle aged stable star • Range is upper left to lower right

  21. Locate Main Sequence Stars

  22. Red Giants & Super Giants, 1% of stars Large Cool Luminous Our sun in 5 billion years will be 2000 times brighter and 100 times larger (large enough to expand past Mars orbit) #2. Upper Right Stars

  23. Locate Red Giants & Super Giants

  24. #3. Lower Left Stars • White Dwarfs, 9% of stars • Small • Hot • Dim

  25. Locate White Dwarfs

  26. Stars Differ in Mass • What is the connection between mass and luminosity? • The larger the amount of matter or mass in a star the more luminous • Giants: more mass - more luminous • Dwarfs: less mass - less luminous • During its lifetime a star will evolve on the H-R diagram depending on its mass.

  27. What is the Absolute Magnitude and Luminosity of Procyon? Rigel? Sun?

  28. Locate Spectral Class New Star (Protostar) Interesting Facts Too much mass- too much internal pressure and outer layers are ejected Not enough mass– not enough pressure and temperature for fusion = brown dwarf Smaller mass stars live longer than larger mass stars

  29. Bibliography • http://www.le.ac.uk/ph/faulkes/web/images/hrcolour.jpg • http://www.unitarium.com/temperature • http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap17/FG17_23.jpg • http://abyss.uoregon.edu/~js/images/40EridanusB.jpg • http://upload.wikimedia.org/wikipedia/commons/thumb/1/15/Redgiants.svg/280px-Redgiants.svg.png • http://startswithabang.com/wp-content/uploads/2008/05/sn1.jpg • http://www.creationofuniverse.com/images/atom/helium.gif • http://www.lancs.ac.uk/ug/hussainw/fusion.jpg • http://www.aip.org/png/images/sn1987a.jpg • http://www.cksinfo.com/clipart/construction/tools/lights/flashlight-large.png • http://www.wildwoodchapel.com/sitebuildercontent/sitebuilderpictures/campfire.jpg • http://projectsday.hci.edu.sg/2001/web%20reports/cat5/14/mstarstructure.jpg • http://webhome.idirect.com/~rsnow/aboutstars.htg/H-RDIAGRAM.gif • http://www.bramboroson.com/astro/images/hrdiagram.jpg • http://outreach.atnf.csiro.au/education/senior/astrophysics/images/stellarevolution/hrwhitecompsml.jpg • http://webs.mn.catholic.edu.au/physics/emery/images/HR%20Evol%20Tracks.jpg • en-US:official%26sa%3DN • http://www.globe.gov/fsl/scicorngifs/Fahrenheit_to_Celsius.jpg • http://images.google.com/imgres?imgurl=http://physics.uoregon.edu/~jimbrau/BrauImNew/Chap17/FG17_23.jpg&imgrefurl=http://blueox.uoregon.edu/~jimbrau/astr122/Notes/Chapter17.html&h=599&w=593&sz=46&hl=en&start=50&sig2=Bi9dN38AcVdfsc3aLNO2TA&um=1&usg=__9mJjqx10-PPxbiWsh4_1Ui7E-G4=&tbnid=IaK0LzJIOKyeaM:&tbnh=135&tbnw=134&ei=_VThSPnkIYboMpnthOkO&prev=/images%3Fq%3Dmain%2Bsequence%2Bstars%26start%3D36%26ndsp%3D18%26um%3D1%26hl%3Den%26client%3Dfirefox-a%26rls%3Dorg.mozilla: • http://images.google.com/imgres?imgurl=http://dhost.info/aquatsr/uranium/elements.jpg&imgrefurl=http://dhost.info/aquatsr/uranium/&h=344&w=599&sz=56&hl=en&start=15&sig2=QKtDKDj4yueFD3YC5ZaBqQ&um=1&usg=__iz2CHra5MXUsXlew6FYezz7s8Hk=&tbnid=y2o_Q6ItHBtLHM:&tbnh=78&tbnw=135&ei=PGrhSKOOK5vUMJCDhfMO&prev=/images%3Fq%3Delements%26um%3D1%26hl%3Den%26client%3Dfirefox-a%26rls%3Dorg.mozilla:en-US:official%26sa%3DG

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