Download File - Mr. Goodyear Astronomy

Spectral classification of stars
- Stars are classified by the temperature and the element spectral
lines found in the star. Classified by letters and numbers
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
Life of the sun / Evolution of Stars
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
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
Stage 4 Main Sequence – “Star Birth” nuclear fusion inside star
core begins makes star hot enough to shine. Converts H He in the
proton-proton 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
- ZAMS – zero age main sequence
Step 5 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.
**All stars go through Red Giant or Red Super Giant stage
Stage 6 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.
Stage 7 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.
Stage 8 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.
The stages of a stars evolution can be plotted on a graph that shows
temperature (K) vs. Brightness absolute magnitude or luminosity:
solar units)
- Graph is known as the Hertzsprung – Russel diagram H-R
diagram
(One of the most important charts in astronomy)