• Galaxies are complex systems of
billions of stars along with gas and
dust, held together by gravity.
• Red shift occurs when the light
source is moving away from the
observer or when the space between
the observer and the source is
• Hubble Law states that the farther
away a galaxy is, the faster it is
moving away from us.
• The Big Bang Theory states the
universe is nearly 14 billion years old At
one point, all energy, matter, and time
existed called a singularity.
• After the Big Bang began the long
process of photons, neutrons, and
electrons forming followed by atoms and
• Mass is not uniform across the universe,
it’s clustered because of gravitational
Dark Matter and Dark Energy
• All mass has a gravitational force, but
astronomers have determined that
there is more gravity in the universe
than visible mass. There must be
another form of mass that can’t be
seen, but has a gravitational pull,
called dark matter.
• Current hypothesis is that the
universe is expanding at a faster rate.
This may be caused by a force called
dark energy. This energy may make
up over 70 percent of the total energy
in the univers.
• Star systems are groups of stars
near each other. Large star systems
are called star clusters. Two types
of clusters: open and globular.
• Open cluster are groups of
thousands of stars held closely
together by gravity. Tend to be
young stars formed out of nebulas.
• Globular cluster are much larger,
containing 100s of thousands of
stars held together by gravity. Pleiades is an open cluster of stars.
Types of Galaxies
• Spiral galaxies spin around a
central force of gravity, often times
massive black holes.
• The Milky Way Galaxy is a spiral
galaxy that is 100,000 light-years
across and 3,000 light-years thick. It
is also believed it contains between
100 to 400 billion stars.
Types of Galaxies
• Irregular galaxies are galaxies that
are neither elliptical or spiral in
shape. Most were originally a spiral
galaxy, but were deformed by a
gravitational force by large galaxy or
collided with a galaxy.
• Dwarf galaxies are the smallest
galaxies, containing only a few
million to a few billion stars. They are
the most common in the universe,
but their small size makes them hard
• Stars form in clouds of dust called
• Stars are made mostly of hydrogen
and helium. Stars are so hot and the
molecules are so packed together
that it can ignite nuclear fusion.
• The energy created has enough force
outward that it balances the star’s
gravitational inward pull.
• The energy released by a star is
called electromagnetic radiation.
• Most stars convert hydrogen into helium and
these stars are in what’s called the main
sequence. Stars are in this stage when
gravitational pull is balanced by nuclear fusion.
• The bigger the star, the more energy it must
consume (aka nuclear fusion) to balance the
gravitational pull by the star. Thus, large blue
giants tend to die sooner than smaller yellow
• Earth’s star is in the main sequence. It formed
almost 5 billion years ago and will stay in main
sequence for another 5 billion years.
• Red giants form when a star has
used up most of it’s hydrogen and
helium and the star’s gravity
becomes stronger than nuclear
fusion. The inner core collapses in
on itself, while the outer shell
• White Dwarfs