Download Ch. 27 Stars & Galaxies

Ch. 27
Characteristics
of Stars
Characteristics of Stars
Composition: The chemicals that makeup the
star
How is composition determined?
Spectrometer: A device that seperates light
into different wavelength.
All chemicals emit different unique
wavelengths of light (spectra)
Spectra can tell a scientist the
elements that are present!
From the spectra data of a newly identified star, an
astronomer concludes that Hydrogen is present in this star.
1. Explain if the scientist is correct.
2. Is Hydrogen the only element found???
Temperature: Indicated by color spectra
Based on this diagram
1. What is the approximate temperature of the
sun?
2. Which stars have the highest temperatures?
3. Which have the lowest temperatures?
The motion of stars
What is your guess for the cause of the stellar motion
shown in these photographs?
Motion of Stars
Apparent Motion: Based on the movement of
Earth.
Motion of Stars
Actual Motion
Red: moving away from earth
Blue: moving towards earth
Distance to the stars
Light Years: The distance that light travels in
one year.
Speed of light is 300,000 km/sec.
Light travels about 9.5 trillion km in one year.
Fun Fact: Light from the sun takes 8 min.
to reach Earth!!!
How can distances between Stars
be measured?
Parallax: Observing stars at different angles
and comparing how they move in comparison
to each other.
Stellar
Magnitude
Brightness of a star.
• Apparent Magnitude
• Absolute Magnitude
Classification of Stars
• Based on Surface Temperatures and
absolute magnitude reveals a pattern
27.2 Stellar Evolution
The Life of a Star
• Scientists have developed theories about the
evolution of stars by studying stars in
different stages of development.
Nebula
•
A cloud of gas and dust
o A nearby force compresses
some of the particles
o As particles collide, increase
in mass, increases gravity
o Eventually forming a
protostar
Main Sequence Star
• The protostar temperature increases due to
•
increased pressure and gravity,
When it reaches 10,000,000 C, nuclear
fusion will begin, and a STAR is born!
• Nuclear Fusion Reactors
H + H  He + Energy
The Life of a main sequence star will
diverge based on the Star’s mass
What happens when Hydrogen
begins to run out???
•
•
•
•
All the Hydrogen is fused into Helium
The core of the star contracts
High temperatures cause the helium atoms to fuse
forming Carbon.
The combined hydrogen fusion and helium fusion
causes the outer shell to expand forming a Giant Star.
What happens when helium fusion ends?
• No energy source available for fusion.
• Star looses its outer gases, core is left,
leaving a planetary nebula or white dwarf
o As the white dwarf cools and no longer emits energy
it becomes a black dwarf.
o Novas: Explosions that occur during the process of
cooling.
Supernovas
• Supergiant Stars that run out of helium
contract with much higher forces.
H + H  He
He + He  Carbon
C + C  Magnesium
Additional fusions form Iron
The collapse if the Iron core causes a massive
explosion = Super Nova
What happens after a Supernova?
• The core of the supernova may contract into a
small dense area of neutrons = neutron star
o Some may emit beams of radiation called pulsars
• If the leftovers from the supernova are too
massive, they may contract under great force
and become a black hole.
Gravitational Pull
• Determined by mass and distance between
objects.
Gravitational pull diagram
HR Diagram Acivities
Warm Up
With your partner, share what you remember
from class
1. How are stars classified?
2. What did magnitude mean?
27.3 Star Groups
• Constellations: Star groups that shift in fixed
patterns as viewed from Earth
• Galaxies: Large groups of star that are
bound by gravitational attractions
Earth is a part of the Milky Way Galaxy!!!
Types of Galaxies
• Spiral galaxies
Example: The Milky Way
Types of Galaxies
• Elliptical galaxies:
Nearly spherical or
flattened disks
Types of Galaxies
• Irregular galaxies: Have no particular shape
• Star Clusters: Clusters of Stars found within
•
a galaxy
Binary Stars: Pairs of stars that revolve
around each other
Formation of the Universe
• Big Bang Theory:
o All matter and energy in the
universe was once concentrated
in an extremely small volume.
o 12 -15 billion years ago, matter
and energy was propelled out into
space.
o Matter began to condense
forming galaxies
o Galaxies and matter continue to
move outward
The End!!