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Introduction to Stars

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Title: Introduction to Stars


1
Introduction to Stars
2
What are the characteristics of a star?
  • Stars differ in
  • Mass
  • Size
  • Temperature
  • Color
  • Luminosity

3
Mass and Composition of Stars
  • 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 Suns 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 Suns mass are extremely
    rare.
  • Our Sun is a medium sized star.

5
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6
Star Energy
  • The enormous pressure and heat in a stars 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.
  • Star stability the energy from fusion
    stabilizes a star by producing the pressure
    needed to counteract gravity.
  • FusiongtGravity expansion
  • FusionltGravity contraction
  • FusionGravity stable

8
Temperature of Stars
  • 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
  • Our Sun is a yellow star having a surface
    temperature of about 5,500ºC

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

10
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, Orange,
    Red
  • O or blue is the hottest (gt25,000oC) and
  • M or red is the coolest (3,500-2,000oC)

11
Classification of Stars
12
Luminosity
  • 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?

13
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 stood in the classroom and person B
    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.

14
Apparent Magnitude
  • The brightness of a star as it appears from Earth
    with the naked eye.

15
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 lt 1 less bright than Sun
  • AM gt 1 brighter than Sun

16
What is the Absolute Magnitude and Luminosity of
Procyon? Rigel? Sun?
17
The Hertzsprung-Russell Diagram
  • An H-R diagram plots stars according to their
    luminosity and temperature (or spectral class)

18
Location of Stars on an H-R Diagram
19
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
  • Upper left stars are
  • Large, hot, luminous
  • Ex. Blue Giants
  • Lower right stars are
  • Small, cool, dim
  • Ex. Red Dwarfs

20
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21
Locate Main Sequence Stars
22
2. Upper Right Stars
  • Red Giants Super Giants (1 of stars)
  • Large
  • Cool
  • Bright
  • Our sun in 5 billion years will be 2000 times
    brighter and 100 times larger (large enough to
    expand past Mars orbit)


23
Locate Red Giants Super Giants
24
3. Lower Left Stars
  • White Dwarfs (9 of stars)
  • Small
  • Hot
  • Dim

25
Locate White Dwarfs
26
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.

27
Bibliography
  • http//www.le.ac.uk/ph/faulkes/web/images/hrcolour
    .jpg
  • http//www.unitarium.com/temperature
  • http//physics.uoregon.edu/jimbrau/BrauImNew/Chap
    17/FG17_23.jpg
  • http//abyss.uoregon.edu/js/images/40EridanusB.jp
    g
  • http//upload.wikimedia.org/wikipedia/commons/thum
    b/1/15/Redgiants.svg/280px-Redgiants.svg.png
  • http//startswithabang.com/wp-content/uploads/2008
    /05/sn1.jpg
  • http//www.creationofuniverse.com/images/atom/heli
    um.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/
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  • http//www.wildwoodchapel.com/sitebuildercontent/s
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    -RDIAGRAM.gif
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    jpg
  • http//outreach.atnf.csiro.au/education/senior/ast
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    pg
  • http//webs.mn.catholic.edu.au/physics/emery/image
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  • en-USofficial26sa3DN
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    nstart50sig2Bi9dN38AcVdfsc3aLNO2TAum1usg__
    9mJjqx10-PPxbiWsh4_1Ui7E-G4tbnidIaK0LzJIOKyeaM
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    6ndsp3D1826um3D126hl3Den26client3Dfirefox-a
    26rls3Dorg.mozilla
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