Stars Characteristics 4/19/2017

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

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. 4/19/2017

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. 4/19/2017

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Star Energy The enormous pressure and heat in a star’s core converts 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. 4/19/2017

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. 4/19/2017

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? 4/19/2017

Star Spectral Classification Astronomers place stars in spectral (color) class categories based on their surface temperature. 4/19/2017

The Spectral Class Letters are OBAFGKM Oh Be A Fine 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) 4/19/2017

Classification of Stars Color Surface temp (ºC) Examples Spectral Class Blue Above 30,000 10 Lacertae O Blue-white 10,000 – 30,000 Rigel, Spica B White 7,500 – 10,000 Vegas, Sirius A Yellow-white 6,000 – 7,500 Canopus, Procyon F Yellow 5,000 – 6,000 Sun, Capella G Orange 3,500 – 5,000 Arcturus, Aldebaran K Red Less than 3,500 Betelgeuse, Antares M 4/19/2017

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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? 4/19/2017

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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. 4/19/2017

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. 4/19/2017

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 4/19/2017

Apparent and Absolute Magnitudes for the ten brightest stars in the night sky Apparent mag. Absolute mag. Sirius -1.44 1.45 Canopus -0.62 -5.53 Arcturus -0.05 -0.31 Rigel Kent -0.01 4.34 Vega 0.03 0.58 Capella 0.08 -0.48 Rigel 0.18 -6.69 Procyon 0.40 2.68 Betelgeuse 0.45 -5.14 Achernar -2.77 The larger the negative magnitude a star has, the brighter it is; but the larger positive magnitude, the fainter the star. 4/19/2017

What is the Absolute Magnitude and Luminosity of Procyon? Rigel? Sun? 4/19/2017

The Hertzsprung-Russell Diagram An H-R diagram plots stars according to their luminosity and temperature (or spectral class) 4/19/2017

Location of Stars on an H-R Diagram 4/19/2017

1. Main Sequence Stars Upper left stars are Large, hot, luminous 90% of stars occur along the main sequence Middle aged, stable stars Main Sequence runs from upper left to lower right Upper left stars are Large, hot, luminous Ex. Blue Giants Lower right stars are Small, cool, dim Ex. Red Dwarfs 4/19/2017

Locate Main Sequence Stars 4/19/2017

2. Upper Right Stars 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) 4/19/2017

Locate Red Giants & Super Giants 4/19/2017

3. Lower Left Stars White Dwarfs (9% of stars) Small Hot Dim 4/19/2017

Locate White Dwarfs 4/19/2017

Star Mass Position 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. 4/19/2017

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 4/19/2017