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Formation of the Solar System
Building Blocks of the Solar System
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We know from observation of the Sun and the other planets that the Solar System is roughly: 74% Hydrogen, 24% Helium, and 2% heavy elements.
So the next question would be: where did these elements come from? Let’s start at the VERY beginning….
Edwin Hubble noticed that galaxies receding from each other, thereby the Universe is expanding
 The rate at which galaxies are receding from each other is proportional to their distance from each other: v=H* d
Where H is the Hubble Constant
 If the Universe is expanding, it stands that at some point in the past everything in the Universe was all concentrated at the same point and began expanding outward. This point in time is called the “Big Bang”
 The Big Bang happened somewhere between 10­16 Billion years ago
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Evidence for the Big Bang
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Oldest stars we see are 12­16 billion years old
More He than stars could ever create Cosmic Microwave Background radiation
COBE Sky Map
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Big Bang hot enough to make Hydrogen and Helium, two elements that make up 98% of the Universes’ present composition, as well as trace amounts of Lithium and Beryllium
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What about the other 2%?
Pleiades Star Cluster
Life Cycle of Stars 
Hertzsprung­Russell diagram plots surface temperature vs. luminosity, end up with a plot showing relative mass, as well as the life cycle of stars
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T Tauri stars start out to the right of the main sequence due to their cooler temperatures. At this time (when the core is roughly 1 Million degrees K), the young star (or protostar) begins fusion of deuterium to helium
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Once the core of the proto star reaches 10 million degrees, hydrogen fusion into Helium (process called the proton­proton chain) starts and the protostar becomes a main sequence star
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Once all the hydrogen fuel is used up, gravity begins to crush the star. Stars die in spectacular fashion, either by expelling their outer layers or as huge super nova explosions. So much heat and energy is produced by these events that all of the heavier elements are formed. Large stars burn through their fuel faster.
Now that we know how and where all of the necessary building blocks of the Solar System came from. Now we can look into the actual formation of our own star, the Sun, and the planet. Sun Formation
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To start forming a star, there needs to be a high concentration of interstellar material
The material needs to be relatively cold so that gravity can overcome the pressure between the interstellar material
Best place for this to happen is in dark nebulae
Lagoon Nebula
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Within the cloud, the internal pressure can not equal the force of gravity, so the cloud begins to contract
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As the protosun contracts, gravitational energy of infalling material is converted to thermal energy and the interior of the cloud begins to heat up
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The cloud had some initial angular momentum (spin in one direction). Due to conservation of angular momentum, as the protosun contracted it began to spin faster
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As the protosun spun faster, the cloud material flattened out into a disk with the majority of the material in the center
Once the interior of the Sun was hot enough, it became a T­
Tauri star, and as it contracted further the interior temperature was enough to begin hydrogen fusion
The Sun is Born
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Once fusion began in the Sun’s core, the internal pressure within the Sun was enough to stop contracting and became a main sequence star