The Sun
The Sun
Size- 1,000,000 Earth
volumes.
300,000 Earth masses.
Distance from Earth93 million miles
(8 light minutes)
Age- 5 billion years.
Halfway through its life.
The Sun
Composition- 71% Hydrogen
27% Helium
2% Heavier elements
Layers of the Sun
Photosphere- The innermost layer of the sun’s
atmosphere. The visible
surface of the sun.
Temp. ~5000 K.
Chromosphere- The
middle layer of the
sun’s atmosphere.
Temp. 30,000 K.
Surface Temp:
5000 K = λ 580 nm
Layers of the Sun
Corona- The outermost
layer of the sun’s
atmosphere.
Temp. 1-2 million K.
Solar wind- A flow of ions
outward into the solar
system from the sun’s
corona.
Nuclear Fusion
Nuclear fusion- The
production of energy
that occurs when
light nuclei combine
to form heavier
nuclei.
Electromagnetic Radiation
Electromagnetic radiation- The transfer of
energy by electromagnetic waves.
The speed of an electromagnetic wave is a
product of its wavelength and frequency.
c = 땃
Wavelength- The distance between two successive wave
crests.
Frequency- The number of waves that pass a given
point per second.
Electromagnetic Radiation
Electromagnetic Spectrum
Electromagnetic spectrum- All types of electromagnetic
radiation arranged according to wavelength and
frequency.
Spectra
Emission line spectrum- The spectrum produced by a gas
contains bright lines at certain wavelengths because each
element present in the gas emits specific wavelengths of light.
Absorption line spectrum- The spectrum produced by a light
source passing through a gas contains dark lines at certain
wavelengths because each element present in the gas absorbs
specific wavelengths of light.
Spectra
A spectrum produced by a star is an absorption
line spectrum.
The pattern of the dark absorption lines of an
element is exactly the same as the bright
emission lines for that same element.
By comparing laboratory emission line spectra of
different gases with the absorption line
spectrum of a star, the composition of the star
can be determined.
Doppler Shift
Doppler shift- A shift
in the wavelength of
electromagnetic
radiation caused by
motion of the light
source.
Doppler Shift
Doppler Shift
Blue shift- If a light source is
moving towards an
observer, the spectral lines
are shifted towards the
shorter wavelength, blue
end of the spectrum.
Red shift- If a light source is
moving away from an
observer, the spectral lines
are shifted towards the
longer wavelength, red end
of the spectrum.
Doppler Shift
Measurements of spectral
line wavelengths can be
used to determine the
direction and speed of a
star’s motion.
Measuring the Stars
Parallax- The apparent
shift in position of a
star relative to other
stars caused by the
motion of the
observer. Parallax is
used to measure
distances to stars.
Parallax
Measuring the Stars
Light-year- The distance
that light travels in one
year at a speed of 3 ×
108 m/s.
Parsec- The distance at
which an object has a
parallax of one
arcsecond.
Equal to 3.26 ly.
Alpha Centauri- 4.3 light years away
Measuring the Stars
Apparent magnitude- How bright a star appears to be as
observed from Earth.
Absolute magnitude- The brightness an object would
have if it were placed at a distance of
10 pc. from Earth.
Luminosity- The amount of energy that a light source
emits per second. Measured in watts.
Hertzsprung-Russell Diagram
Hertzsprung-Russell
diagram- Demonstrates
the relationship between
a star’s temperature and
luminosity.
Stars are classified based
on where they plot on a
H-R diagram.
Stellar Evolution
Hydrostatic equilibriumThe gravitational force
that compresses a star
inward is balanced by
the nuclear fusion force
that expands a star
outward.
Stellar Evolution
Nebula- A cloud of
interstellar gas and dust
which collapses in on
itself as a result of its
own gravity.
Stellar Evolution
Protostar- A hot,
condensed object at
the center of a nebula
where nuclear fusion
begins.
Stellar Evolution
Main sequence- A star
like our sun converts
hydrogen into helium
in its core for
approximately 10
billion years.
Stellar Evolution
Red giant- When the
hydrogen in the core
of a star is used up,
the outer layers of
the star expand and
cool. The star
becomes more
luminous as it cools.
Orion
Rigel
Betelgeuse
Sun at 8 A.U.
Betelgeuse at 8 A.U.
Stellar Evolution
White dwarf- When
hydrogen fusion ends,
the red giant star
contracts and helium
fuses in the core to
produce carbon. When
helium fusion ends, the
star collapses into a
small, hot, extremely
dense object about the
size of Earth.
Stellar Evolution
Stages of fusion in small to average stars:
H  He
He  C
Stages of fusion in massive stars:
H  He
He  C
C  Fe
Stellar Evolution
Neutron star- Protons
and electrons in the
core of this massive,
collapsed star merge
to form neutrons,
leaving a star more
massive than the sun,
but only 10 km in
radius.
Stellar Evolution
Supernova- In stars
that begin life with
more than 8 times
the mass of our sun,
the iron core that
remains after carbon
fusion ends,
collapses in on itself,
producing a violent
explosion.
Crab Nebula of A.D.1054
Supernova in Large Magellanic
Cloud in 1987.
Stellar Evolution
Black hole- When stars
with more than 20 times
the mass of our sun
exhaust their fuel, the
resistance of neutrons in
the core cannot stop the
gravitational collapse,
and the core of the star
continues to collapse in
on itself, compacting
matter into an eversmaller volume.
Red Dwarf
Nearest Stellar Neighbors
Nearest supergiant- Betelgeuse 600 ly
Nearest black hole- 1600 ly
Closest safe distance from a supernova- 50 to100 ly