Stars Characteristics

1. Stars Characteristics

2. What are the characteristics of a star? Stars differ in… • Mass • Size • Temperature • Color • Luminosity *Stars can be plotted using these characteristics on a chart or HR diagram

3. Star Mass and Composition • Mass and composition determine 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. Star Size • The diameters of stars range from as little as 1/10 the Sun’s diameter to hundreds of times larger. • The mass of stars can be from less than 1/100 to 20 or more times that of our Sun. • Stars over 50 times the Sun’s mass are extremely rare. • Our Sun is a medium sized star.

6. Star Energy • The enormous pressure and heat in a star’s core converts matter into energy. • Stars consist of controlled atomic reactions called nuclearfusion 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. • Star stability – the energy from fusion stabilizes a star by producing the outward pressure needed to counteract the inward force of gravity. • Fusion>Gravity = expansion • Fusion<Gravity = contraction • Fusion=Gravity = stable • NOTE: Stable stars are plotted on the HR diagram.

8. Star Temperature • Stars in the sky show tinges of different colors which reveal the stars’ temperatures. • Blue stars shine with the hottest temperatures and red stars shine with the coolest temperatures. • Our Sun is a yellow star having a surface temperature of about 5,500ºC Stop and Think • The hottest flame color in a campfire is?

9. Star Spectral Classification • Astronomers place stars in spectral (color) class categories based on their surface temperature.

10. The Spectral Class Letters are OBAFGKMOh Be AFine Girl/Guy Kiss Me Star colors from Hottest to Coolest: Blue, Blue-White, White, Yellow-White, Yellow, Orange, Red • O or blue is the hottest (>25,000oC) and • M or red is the coolest (3,500-2,000oC)

11. Classification of Stars

13. Star Luminosity/Brightness • The energy output from the surface of a star per second measured in watts. • The brightness of a star depends upon the distance and its luminosity. Stop and Think • The star Rigel in Orion is about 60,000 times larger than our Sun. • Why does our Sun appear brighter than Rigel?

15. Stop and Think If person A has a pen flashlight and person B has a mega flashlight and both were standing at the front of the classroom, which light would appear brighter? If person A (pen light) stood in the classroom and person B (mega light) stood at the baseball fields across the street, which light would appear brighter? You cannot tell by looking in the sky how bright a star truly is. The farther away the star is, the less bright it will appear.

16. Apparent Magnitude • The brightness of a star as it appears from Earth with the naked eye. As you can see, the magnitude numbers are bigger for faint stars, and magnitudes are negative for very bright stars.

17. Absolute Magnitude • The true brightness of a star if all stars were at a uniform distance from Earth • The absolute magnitude of stars is reported in comparison to our Sun. • Ex. AM of Sun = 1 AM < 1 : brighter than Sun AM > 1 : less bright than Sun

18. Apparent and Absolute Magnitudes for the ten brightest stars in the night sky The larger the negative magnitude a star has, the brighter it is; but the larger positivemagnitude, the fainter the star.

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

20. The Hertzsprung-Russell Diagram • An H-R diagram plots stars according to their luminosity and temperature (or spectral class)

21. Location of Stars on an H-R Diagram

22. Upper left stars are Large, hot, luminous Ex. Blue Giants Lower right stars are Small, cool, dim Ex. Red Dwarfs 1. Main Sequence Stars 90% of stars occur along the main sequence Middle aged, stable stars Main Sequence runs from upper left to lower right

23. Locate Main Sequence Stars

24. Red Giants & Super Giants (Super Super Giants, too) Large Cool Bright 1% of stars 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

25. Locate Red Giants & Super Giants

26. 3. Lower Left Stars • White Dwarfs (9% of stars) • Small • Hot • Dim

27. Locate White Dwarfs

28. Star MassPosition on H-R depends on mass • The larger the amount of mass in a star, the more luminous it is. • 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/ • http://images.google.com/imgres?imgurl