Ch. 15 Notes
Transcript Ch. 15 Notes
Chapter 19 The Universe
Chapter 15 The Universe
Types of stars
• Color and
temperature of stars
both depend on the
size of the star.
Bigger stars are
hotter. Smaller stars
• Colors of stars
Surface Temp. 0C
B Blue-White (10,000-30,000)
– Scientists can analyze
the light coming from
stars to determine the
types of elements
present in the star
– Black lines indicate the
light absorbed by
specific elements in
• How bright a star appears to be from Earth
– Our sun appears to be the brightest star in the
sky because it is the closest ( -26.8 on the
apparent mag. scale)
• How bright a star actually is, as if all stars
were the same distance away
– Our sun is only average compared to other
(+4.8 on the absolute mag. scale).
• Scientist use a method called parallax to
calculate the distance of stars.
Closer stars seem
to move more
Earth in July
Parallax causes nearer stars to
appear to move more over the course
of the year.
Constellations are used as maps to help guide our way as we look at the stars
above. The names and “pictures” they appear to form come from stories from
• Canis Major (The big dog)
– Sirius, one of the brightest stars in or night
sky, is called the Dog Star, and the hot
summer season is called the dog days
since Canis Major rises at the height of
• Cassiopeia (The Vain Queen)
– Found near the celestial north pole.
– In the Greek legend she bragged about
her beauty and was punished by the sea
god, Poseidon, who placed her in the sky.
• Cygnus (The Swan)
– In the Greek legend Zeus disguised
himself as a swan from time to time.
– Its brightest star, Deneb is one of the
brightest stars in the sky
– Seen in the summer night sky.
• Orion (The hunter)
– Easily identifiable by the three stars of his
belt during the fall and winter
– Betelgeuse, the hunter’s right shoulder, is
a red supergiant star. If it was in our sun’s
place it would extend to the orbit of Jupiter.
It will explode in a supernova explosion
sometime in the next 1000 years. When
this happens it will be brighter than the full
moon and even visible during the day for
– There are several interesting objects
located around this constellation.
The distance between stars is
measured in light years ( the distance
light travels in one year) because they
are so far apart.
– The next nearest star to our sun is 4 light
years ( nearly 38.7 trillion kilometers away
or 252,000 A.U.)
The Life Cycle of Stars
• Smallest, coolest, dimmest stars
– Less than 1 solar mass
• Last the longest, 100 billion years
Although they are less visible than the brighter blue
and white stars, 2/3 of the 370 stars closest to Earth
are red dwarf stars. The closest star after our sun is
Proxima Centauri, a red dwarf seen from the
centauri is our closest neighbor
star after the sun.
• Like our sun, medium size and
– Around 1 solar mass
• Last for 10 billion years
• Largest, hottest, brightest stars
– 5 solar masses or more
• Shortest lasting stars, maybe only 10
Red Giants/ Supergiants
• Dying stars that are running out of fuel
• These stars (former red, yellow and blue
stars) have swollen up due to internal
pressure, their surfaces have cooled
• Small, shrunken stars that no longer have fusion
• They glow only due to the high temperature of
their cores, heat gathered from when they
burned their fuel.
• They become black dwarves when they cool
enough to stop glowing.
How a star dies depends on its
size and temperature
• Small stars lead quiet, calm lives and have
quiet, calm endings
• Large stars lead short, violent lives and
have violent endings
(smaller than our sun)
before using up all of their hydrogen fuel.
Red dwarves live as long as 100 billion years
2 , many times
2. They will swell into
larger than it was before.
When the fusion process fails gravity causes the
star to shrink into a white dwarf ( about the
size of its core), which will slowly cool into a black
( like our sun)
Yellow stars like our sun will be able to
continue the fusion process for 10 billion years.
As the fuel runs out they will swell into red
giants. Sometimes the star may shrink and
swell repeatedly, called a variable star.
These red giants may blow off their outer
layers as rings of gases, called planetary
nebula, as the last of its fuel is spent.
When the fusion process fails gravity
causes the star to shrink into a white dwarf
( about the size of its core), which will slowly
cool into a black dwarf.
(several times larger than our sun)
White and blue giants burn up their
fuel in as little as 10 million years.
These stars swell into red supergiants,
some as big as our entire solar system.
These may shrink and swell before
they finally explode in a massive
a. Supernovas create all of
the larger elements in one instant.
b. Supernovas are as bright
as the entire galaxy for a short time
before they begin to fade.
c. The outer layers are
blown outward, the inner layers are
blown inward creating super-dense
cores called neutron stars, which are
only 20-100 km across, but are still
heavier than our sun.
d. A spinning neutron star is called a pulsar
because the beam of energy from the pole
sounds like a pulse on Earth.
e. A very large star creates a very small neutron
star, called a black
*Black holes are at least three
times more massive than our
sun but less than 10 km across
• A black hole is the core of an
exploded star. The material is so
dense that the speed needed to
escape it is faster than the speed
of light. This means that any
object that gets too close would
not be able to escape.
• The existence of black holes was
first proposed by Albert Einstein
as a result of his Theory of
General Relativity. He called
them “dark stars”, but suggested
these monsters could not
possibly exist for real.
• They have been observed due to
the effect of their massive
amounts of gravity on
H-R Diagram is a chart comparing a star’s brightness
(luminosity) to its surface temperature.
stars are normal
“adult” stars not in
the process of dying
Surface Temperature (0C )
Proxima Centauri 10.3
Red Giant (supergiant)
Types of Galaxies
• Spiral galaxies have a central bulge and
distinctive spiral arms
• Our home galaxy, the Milky Way, is an example
• Formed slowly, giving time for gravity to create the
• Elliptical galaxies are spherically shaped
and have been cleaned out of nebula,
which means few new stars are forming
• Form quickly, before gravity has a chance to
change the shape
• Irregular galaxies do not fit the other
• These are small galaxies being distorted by gravity
from other nearby galaxies
Large Magellanic Cloud (LMC) –
a neighbor to our Milky Way Galaxy (a satellite to our
galaxy). It was seen by Ferdenand Magellan as he circled the world. It can
only be seen from the southern hemisphere.
Galaxies have several parts
o Each star is its own solar system
(containing planets and other objects)
o Nebula (gas and dust clouds where
new stars form), seen as dark lines.
• Active galaxy centers
– Supermassive black holes
are thought to be at the
center of most galaxies.
• Contain millions of solar
• Quasars are very distant
objects only visible because
they emit huge amounts of
energy. These are massive
blackholes eating material.
Quasars are the brightest
objects in the universe and
are used to measure the
size of the universe.
The Big Bang Theory
The Big Bang Theory describes the formation of the universe resulting from a
massive explosion of a single object which generated all matter and energy that
currently exists in the universe. This model explains the observations being made
and has been confirmed by huge amounts of data.
Working backwards scientists have
determined that the Big Bang Event
occurred 14 billion years ago.
While new evidence and
observations all continue to confirm
this theory, new discoveries seem
to indicate that the universe is
accelerating as it expands. This
was not expected and is difficult to