Introduction to Stars

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. Composition • Through spectroscopy, the dark lines (or bright 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.

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

4. 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.

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.

7. 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.

8. Star Energy cont. • The energy released causes the star (Sun) to shine and gives the star its high temperature. • Star stability – this energy stabilizes a star by producing the pressure needed to counteract gravity. • Fusion>Gravity = expansion • Fusion <Gravity = contraction • Fusion = Gravity = stable

9. 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.

10. 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

11. 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

12. Spectral Type Classification • Astronomers place stars in spectral (color) class categories based on their surfacetemperature.

13. Classification of Stars

14. 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)

15. Absolute magnitude • The true brightness of a star if all stars were at a uniform distance from Earth • 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.

16. Apparent Magnitude • The brightness of a star as it appears from Earth with the naked eye.

17. 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?

18. 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) • An H-R diagram plots stars according to their luminosity and temperature (spectral class) • About 90% of stars including the Sun fall along a broad strip of the H-R Diagram called the Main Sequence.

19. Included in the H-R Diagram will be: • Temperature 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 • Absolute Magnitude is in comparison to the Sun (

20. HR Diagram cont • Stars that are part of the Main Sequence indicate that all these stars have similar internal structure and functions.

21. Stars are grouped into types by temperature and luminosity

22. 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

24. Locate Main Sequence Stars

25. 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

26. Locate Red Giants & Super Giants

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

28. Locate White Dwarfs

29. Position on H-R Depends on 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.

30. 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