The UniverseGEOG 1000: Physical Geography

Expanding Universe

• Galaxies are complex systems of billions of stars along with gas and dust, held together by gravity.

Expanding Universe

• Red shift occurs when the light source is moving away from the observer or when the space between the observer and the source is stretched.

• Hubble Law states that the farther away a galaxy is, the faster it is moving away from us.

Expanding Universe• 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. https://www.youtube.com/watch?v=gs-yWMuBNr4#t=105

• After the Big Bang began the long process of photons, neutrons, and electrons forming followed by atoms and molecules.

• Mass is not uniform across the universe, it’s clustered because of gravitational forces.

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• 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 to see.

Star Energy• Stars form in clouds of dust called nebulas.

• 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.

Star Classification• 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 stars.

• 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.

Star Classification

• 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 expands.

• White Dwarfs