Transcript The Sun . . .

Star Classification:
The Sun . . .
And Other Stars!
Sun Stats;
Mass: 333,000
times greater than
Earth; ~ 2.0 x 1030
kg
Composition:



73% hydrogen
25% Helium
2% ‘other’ (oxygen,
carbon, etc.)
Surface Temp: ~
5800 K
Rotation:


27 Days
We rotate in 1 day!
Diameter:


1,392,000 km
That’s 109 times
greater than Earth!
Sun’s Energy
The Sun’s energy comes from nuclear
fusion – when light hydrogen nuclei
combine to form heavier helium nuclei.
These reactions occur in the Sun’s core
The Sun should have enough fuel to
continue burning for about 5 billion more
years; nothing we need to worry about!!
Sun’s layers, from inside out:

Core


Radiative Zone


Converts energy from fusion reaction to radiation
Convective Zone


Site of fusion
Convection currents carry energy to surface
Photosphere

Emits most light radiation
A plain, old, mediocre star . . .
Scientists describe the physical properties of
other stars in the universe by comparing them
with the physical properties of the Sun.
The physical properties of stars are:

Mass, density, diameter, magnitude, luminosity,
and surface temperature.
Magnitude is the brightness of stars; the
brighter the star, the lower its magnitude.
Luminosity is the brightness of a star
compared to the Sun, with the Sun being 1.
Anything brighter than the sun is >1, anything
dimmer is <1.
Hertzsprung-Russell (H-R) Diagram
The H-R diagram classifies stars according to their
luminosity (absolute magnitude) and spectral class
based color and surface temperature.
Life cycle of the Sun
The Sun is at the mid-life point of its predicted
10 billion year life.
It started as a nebula and is now at the main
sequence stage where fusion will continue
until the hydrogen is used up.
The Sun will then enter the Red Giant phase
where it expands and grows cooler and more
luminous.
Its final stage is white dwarf, after it collapses
upon itself and only the hot, dense core will
remain.
Sun’s life cycle . . .
From nebula to main sequence to red giant to
white dwarf
Let’s look at vocab:
H-R Diagram: Diagram that classifies stars
according to their luminosity/absolute
magnitude, and spectral class based on color
and surface temperature.
Luminosity: The brightness of a star
compared to the Sun.
Absolute Magnitude: Compares the
brightness of stars from a standard distance
from Earth.
More vocab . . .
Apparent magnitude: How bright a star
appears to be from Earth ~ not very
‘scientific’.
Main Sequence: Average, ordinary stars. ~
90% of stars are main sequence.
Supergiant: 20 to 200 times larger than the
Sun, but also much brighter, cooler and less
dense.
Dwarf: Small stars; fairly hot but very dim.
Diameter is about the same as Earth, but
their mass is equal to the sun . . .
Star color;
As stars get cooler,
then change from
blue to red.
Red = cooler stars,
Blue = Hotter stars
White dwarfs are
dim because they
are so small.
Red giants are
bright because they
are so big.
In order for a cool
star to be bright, it
must have a very
large diameter.
Deneb & Rigel ~ Nearby supergiants
If Deneb and Rigel were as close as the
Sun, they would appear exceptionally
bright!
Deneb and Rigel are
about 100,000 brighter
than the sun!!