AST101H1 Lecture Notes - Galilean Moons, Milky Way, Copernican Revolution

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19 Mar 2013
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Chapter 1 11/16/2011 8:32:00 AM
Chapter 1:
What is our place in the universe?
Geocentric: Earth-centered universe
Solar system: the planets and their moons, and countless smaller
objects including rocky asteroids and icy comets
Galaxy: a great island of stars in space, containing from a few
hundred to a trillion or more stars
Galaxy clusters: groups od galaxies with more than a few dozen
members
Supercluster: regions in which galaxies and galaxy clusters are
most tightly packed (clusters of galaxy clusters)
Universe: the sum total of all matter and energy, encompassing the
superclusters and voids and everything within them
Universe is expanding at a decreasing acceleration rate
The Big Bang and Expanding Universe
Big Bang: when the expansion of the universe began (14.4 billion
years ago)
Galaxies/ galaxy clusters occur where gravity was stronger than the
expanding force of the universe
Stellar lives and galactic recycling
Gravity causes clouds of gas and dust to collapse and form stars
and plants
A star is created due to nuclear fusion; gravity compresses the
material in a cloud to the point where the centre is dense enough
and hot enough to generate energy by nuclear fusion
A stars life span only lasts as long as it can shine with the energy
from the fusion
When a star runs out of energy and "dies", it explodes and most of
its content is blow out into space
Supernova: the explosion of a dying star
New stars are born when the matter from older stars floating
around in the galaxy form new clouds of dust and gas
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Stars manufactured the elements of earth and life
The early universe only contained hydrogen and helium
The other elements that exists today were created by stars (nuclear
fusion and supernovae)
How can we know what the universe was like in the past?
By studying light from distant stars and galaxies we can see into
the past
"The farther away we look in distance, the further back we look in
time."
And picture we see of galaxies is a shot of both space AND time
14.4 billion light years is the boundary of our potential observation
How is earth moving in out solar system?
The Earth rotates daily and orbits the sun annually
Rotates from west to east (counter-clockwise as seen from above
the North Pole)
Earths average orbital distance = 1AU (150milliom km)
Ecliptic plane: earths orbital path (flat plane)
How is our solar system moving in the Milky Way Galaxy?
Stars @ diff. distances from the galactic centre orbit @ diff. speeds
o We can use these speeds to determine how mass is
distributed in the galaxy
Halo: the area of a galaxy outside its visible disk, where the mass
of the galaxy is located (made up of dark matter)
Dark matter: matter from which no light is emitted/ reflected
o Galaxies are made mostly of dark matter
o Significantly outweighs regular matter that planets and stars
are made of
Are we ever sitting still?
Our galaxy is constantly moving among the galaxies of our local
group, while all other galaxies move away from us in the expanding
universe
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