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Astronomy
Big Bang theory – Origin of the Universe
Big Bang marks the beginning of the universe
• Occurred about 15 billion years ago
• All matter and space was created
Not a huge explosion that hurled matter in
all directions. Technically, there was no
“bang”
Technically, matter is not moving outward in
all directions. Reality: space expands
Raisin bread analogy of an expanding
universe
Origin of the Universe
The structure of the Universe
A galaxy is a collection of billions of stars held
together by gravity
The universe contains
billions of galaxies
and each galaxy
contains billions of
stars.
Our galaxy is a spiral
galaxy called the
Milky Way
What makes objects in space keep moving?
1. Gravity -- a force of attraction between
objects
Greater mass = greater gravity
Greater distance = less gravity
Weight is a measure of the pull of
gravity
Is weight the same as mass?
NO!
Weight changes due to gravity; mass stays the same
2. Inertia -- an object in motion stays in motion and an object at
rest stays at rest, unless acted on by a different force
What would life be like without gravity?
Rotation vs. Revolution
Rotation: an object spinning on its axis
Revolution: an object orbiting around another object or
point in space
Two forces keep objects
moving in space:
1. gravity – the force of attraction
between objects with mass
2. inertia – an object will continue
doing what it’s doing unless acted on
by a different force
Gravity pulls gases and dust in space together to form planets,
moons, and stars
Where do stars come from?
Stars form in nebulae where gases condense and nuclear
fusion reactions generate tons of energy
Orion Nebula
Rosette Nebula
Betelgeuse
Orion Nebula
Rigel
Not all stars in a constellations are
actually near each other
All stars are not alike in size, color, or
brightness
Stars are very different from each other, depending on their mass and
place in their life cycle
HIGH MASS
STARS
LOW MASS
STARS
Our Sun is actually a very average star in the
middle of it’s life cycle....medium brightness ,
temperature, and size
Stars form in gas nebulas
They enter the main sequence at various
points depending on how much mass they
collect
The Sun (and our solar system) is about 5 billion years old.
Stars get their energy from nuclear fusion