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Lecture 11

ASTA01H3 Lecture Notes - Lecture 11: Harlow Shapley, Edwin Hubble, Planetary System

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Kristen Menou

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Lecture 11
Humans have inhabited the solar system for at least a million years. However, only
within the last
2400 ears hae e egu to realize that e lie i a osos ad a plaetar sste
400 years have we begun to understand the details of the true heliocentric
arhiteture of our solar sste
300 years have understood its mechanics
200 years have we started to make detailed scientific models of its origin
100 years have sensed that its haoti et stale, ad here it is loated i a Gala
90 years have we completed the Copernican revolution: Harlow Shapley removed the
Sun from the center of the Galaxy, and Edwin Hubble the Galaxy from the center of the
50 years have we figured out ho the su orks ad ho the stars produed the
atoms in our bodies
30 years have we begun to observe & understand details of star formation such as
protostellar disks and their relevance to our origins
20 years have we begun to observe direct evidence for planetary systems other than our
10 years have we placed our system in a wider context and compared it with hundreds
of newly discovered extrasolar systems
You are linked through a great chain of origins that leads backward through time to the
first instant when the universe began 13.7 billion years ago
By the time the universe was three minutes old, the protons, neutrons, and electrons
now in your body had come into existence.
You are made of very old matter (13.7 Gyr old)
Although those particles formed quickly, they were not linked together to form the
atoms that are common today.
Most of the matter was hydrogen (almost 75%)
and about 25% was helium.
Very few (< 1%) of the heavier atoms were made in the big bang.
The big bang also formed the so-called dark matter, which permeates the planetary
systems at very low density, but has very little interaction with them.
We are made mostly of water, and water is made mostly of hydrogen (counting the
atoms), and of oxygen (which dominates our mass)
During the first few hundred million year after the big bang, matter collected to form
galaxies containing billions of stars. Our Galaxy was built ~8.8 Gyr ago
nuclear reactions inside stars combine low-mass atoms, such as hydrogen, to make
heavier atoms.
Most of the iron in your body was produced by Carbon fusion in the explosions of stars
called supernovae, and Decay of radioactive atoms in the expanding matter ejected by
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