Download File - Mr. Goodyear Astronomy

Objectives: S.W.B.A.T.
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Understand the classification of stars –
spectral class
Label stages of an average main sequence
star to an H-R diagram
Define/describe stages the of the sun’s
life cycle from birth to death
Activities:
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Warm-up
Finish video spectrum light color
Notes/discussion
Microslide review - sun
Spectral classification of stars
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Stars are classified by the temperature
and the element spectral lines found in
the star. Classified by letters and numbers
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O B A F G K M “oh be a fine girl/guy kiss me”
Each has 10 sub categories numbers from
0 to 9
The size and brightness is also classified by Roman
numbers/letters
 Ia – Bright Supergiants
 Ib – Supergiants
 II – Bright Giants
 III – Normal Giants
 IV – Subgiants
 V – Main Sequence
Our sun is classified as a G2V
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Life of the sun / Evolution of Stars
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Stage 1 Nebula – a huge cloud of gas &
dust mostly of hydrogen collects and
contracts due to gravity. 2-5 billion years
100 trillion-1 billion km in diameter (light
years across)
Stage 2 Protostar – prestart that is not
hot enough to shine in visible light (shines
in radio waves to infrared energy) size
ranges from 300,000 X of solar system to
10,000 X diameter of the sun.
-time span last around 100,000 years
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Stag 3 T-Tauri – a class of variable star prior
to main sequence, 1st discovered in
constellation in Taurus. Stars are the same
mass, as main sequence, but they are
significantly more luminous because their radii
are larger. Temperature in core is to low for
nuclear fusion.
Powered by gravitational energy. (Size rage:
1000 X diameter of sun) last in this stage ~ 100
million years
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Stage 4 Main Sequence – “Star Birth” nuclear
fusion inside star core begins makes star hot
enough to shine. Converts H
He in the protonproton cycle. 90% of stars are main sequence
stage. Stars are said to be in Hydrostatic
Equilibrium: energy output = gravitational pull
inward (known as hydrogen burning stage)
Stars like our sun last 10 billion years as a main
sequence
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ZAMS –zero age main sequence
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Step 4 Helium Flash / Red Giant – as
hydrogen in core of star decreases and helium in
core rises, the star starts to become unstable
and equilibrium breaks down, gravity takes over
– causing greater pressure on core and causes
helium flash or fusion (new energy He C ) Star
grows: increase energy overcomes gravity, star
moves off the main sequence to red giant area
of graph.
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**All stars go through Red Giant or
Red Super Giant stage
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Stage 5 Planetary Nebula / Nova - star uses up most of
He and moves back toward main sequence area of H-R
diagram.
Star fluctuates on and off main sequence. Gravity tries to
contact star creating other elements in star increasing fusion
process.
This increase energy causes an explosion-like occurrence. This
cause star to lose large quantities of mass.
Also during this time period star sheds off excess gas
envelopes, which appears as a ring around star when viewed
from a distance.
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Stage 6 White Dwarf – Star continues
the fusion process He to C, and C to O
and Ne, O, to Si. Star burns hot due to
gravitational pressure. The average white
dwarf is about the size of a large planet.
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Stage 7 Black Dwarf – final stage of a
low mass main sequence star. All fusion
stops core dies out no fuel. What remains
is a dense silicon rock ~ 90% +/- of the
original stars mass.
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The stages of a stars evolution can be
plotted on a graph that shows
temperature (K) vs. Brightness absolute
magnitude or luminosity: solar units)
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Graph is known as the Hertzsprung –
Russel diagram H-R diagram
(One of the most important charts in
astronomy)