Download Chapter 19 Notes Stars Stars are bright balls of gas that are trillions

Chapter 19 Notes
I. Stars
a. Stars are bright balls of gas that are trillions of kilometers away from
Earth
b. The color of stars indicate their temperature
i. Red and yellow are cool stars, like our sun
ii. Blue and white are hot stars.
c. Astronomers use an instrument called a spectrograph to break a
star’s light into a spectrum
i. Spectrum- a band of colors produced when white light passes
through a prism.
ii. When an element emits light, only some colors of the
spectrum show up.
d. Emission Lines
i. Lines made when certain wavelengths of light or colors
ii. Are given off by hot gases.
iii. Each element has a unique set of bright emission lines
e. Stars are classified according to how hot they are.
i. Temperature differences in stars result in color differences
that you can see.
ii. Blue stars are the hottest, red stars are the coolest.
f. Apparent Magnitude
i. The brightness of the star as seen from Earth.
ii. Some stars are brighter than others because of their size or
energy output, not because of their distance from Earth.
g. Absolute Magnitude
i. The actual brightness of a star
ii. Astronomers use a stars apparent magnitude and its distance
from Earth to calculate it.
h. Astronomers use light years to measure distances from Earth to the
stars
i. 1 Light year= 9.5 trillion kilometers
i. Parallax
i. A star’s apparent shift in position
ii. Stars near the Earth seem to move, while stars that are more
distant stars seem to stay in one place as the Earth revolves
around the sun.
j. During each season, the Earth faces a different part of the sky at
night. This is why we see different constellations at different times of
the year.
i. All of the stars you see appear to revolve around Polaris, the
North Star, which is almost directly above the North Pole.
ii. The stars make one complete rotation around Polaris every 24
hours.
II. Life Cycle of Stars
a. A star is “born” when gravity begins to pull a ball of gas and dust
together into a sphere.
i. As the sphere gets denser, it gets hotter and nuclear fusion
(the combining of hydrogen atoms together to form helium)
begins.
b. After a star forms, it enters the second and longest stage of its life
known as the Main Sequence
i. During this stage, energy is made in the core as hydrogen
atoms fuse into helium.
c. Giants and Super Giants
i. After the main sequence stage, the star enters the third stage
of its life.
ii. A red giant is a star that has cooled and expanded as it uses up
all of its hydrogen.
iii. If a star is very large, when it begins to use up all of its
hydrogen, it expands to become a supergiant.
d. White Dwarfs
i. This is the last stage of a stars life.
ii. A white dwarf is a small hot star that is the leftover core of an
older star.
iii. A white dwarf has no hydrogen left and cannot generate
energy anymore.
iv. White dwarves can shine for billions of years before burning
out completely.
e. H-R Diagram
i. Also known as a Hertzsprung Russell diagram
ii. A graph that shows the relationship between the surface
temperature and the absolute magnitude (brightness) of a
star.
f. When stars get old
i. While many stars become white dwarves as they get older,
very massive stars can become strange objects like pulsars,
supernovas, black holes and neutron stars.
ii. Supernovas
1. Massive stars use their hydrogen much faster than stars
like the sun do.
2. At the end of their lives they may explode in a bright
flash called a supernova.
3. This gigantic explosion happens when the star collapses
and throws its outer layers out into space.
iii. Neutron Stars and Pulsars
1. After a Supernova, the center of the collapsed star
contracts to form a new star, called a neutron star
2. The mass of this star is 2 times the mass of the sun.
3. If the neutron star is spinning, it is called a pulsar
iv. Black Holes
1. If the center of a collapsed star has a mass that is more
than 3 times the mass of the sun, the star may contract
further because of its own gravity.
2. The force of this gravity crushes the dense center of the
star and leaves a black hole.
3. A black hole is so massive that light cannot escape its
gravity.
III. Galaxies
a. Galaxies are large groups of stars, dust and gas.
b. Types of galaxies
i. Spiral (like our Milky Way)
ii. Elliptical
iii. Irregular
c. Galaxy Contents
i. Nebula- clouds of dust and gas where stars are born
ii. Star Clusters
1. Globular Clusters- groups of older stars
2. Open Clusters- groups of closely grouped younger stars
d. Quasars
i. The most distant objects in space
ii. May be caused by giant black holes in the cores of galaxies
IV. Origin of the Universe
a. The study of the origin, structure and future of the universe is known
as cosmology
b. To understand the formation of the universe, scientists have looked
at the movement of galaxies to see that the universe appears to be
expanding as galaxies move away from one another.
c. Balloon example- Describe what happens.
d. The Big Bang Theory
i. If the universe is expanding, if you could rewind the expansion,
all the matter in the universe would come together in one
single point.
ii. The Big Bang Theory states that the universe began with a
tremendous explosion 13.7 billion years ago.
iii. All the matter in the universe was compressed under extreme
pressure, temperature and density into a tiny spot.
iv. Then, the universe rapidly expanded and matter began to
come together to form galaxies
v. Scientists don’t know if the universe will keep expanding as
time continues or if it will reach a point and then begin to
contract again.