The Solar System
Our solar
system includes the Sun and the accoutrement of objects, of which Earth is just
one of many, that are gravitationally bound to it. We didn’t always see it this
way. Until recently, we didn’t know anything about gravity and how it worked to
shape the solar system. We thought that the Earth was the center of the
magnificent celestial tapestry that wraps around us. Those of you brave enough
to take this class will learn how humans slowly and excruciatingly gave up this
centrist viewpoint, eventually replacing it with a more egalitarian perspective
about our overall place in the grand scheme of things.
An arguable case can
be made that modern science began with the struggles of the ancient Greeks to
understand the nature of the heavens that seemed to revolve around them.
Consequently, we will spend a sizeable amount of time discussing the early
history of astronomy and the first ideas that a few great early thinkers had
about the way the cosmos worked. We will see how a few ancient peoples, in the
process of worrying and thinking about the apparent motions of objects on the
celestial sphere, developed incredibly profound models of the cosmos, some of
which were so mathematically sophisticated that the complexity of their
constructs exceeds the grasp of most people today, even those who call
themselves educated. We will see that the thought processes the ancient Greeks
put in place in order to explain their observations, though not quite correct,
nonetheless were crucial steps that had to be taken if humans were to escape
the shackles of ignorance that they seemed determined to bound themselves up
in.
We
will see how the development of science took a quantum leap forward during the
renaissance of the 16th and 17th centuries, when one
great man, Tycho Brahe, saw the importance of making detailed observations of
the position of celestial objects with unprecedented precision and when one of
his colleagues, Johannes Kepler, used those observations to construct one of
the first accurate mathematical models of the solar system. The work of these
two men showed us how the emergence of scientific knowledge depends critically
on the symbiotic relationship between observation and theory, which is the
cornerstone of modern science.
We
will see how another man of that notable era, Galileo Galilei, known as the
“father of science,” simply could not see the rationale behind the centuries
old dogma that man occupied the center of the cosmos. Instead, he embraced the
newly emerging idea that man’s place in the scheme of things was notable only
for its mediocrity and he made observations with a newly developed instrument
that, though they strongly supported this new paradigm, did not unequivocally
prove it to be so --- an unfortunate circumstance that would ultimately place
Galileo in great jeopardy. On the same day of Galileo’s death, Sir Isaac Newton
was born. He would finally put it all together, publishing his work in 1687 in
what arguably is the world’s most significant scientific publication, the Philosophiae
Naturalis Mathematica Principia, known simply as the Principia. The
resounding thump of the fall of man from his central place of grace would be
heard around the world as thousands upon thousands of scholars opened the pages
of that magnificent work. No educated person who read this publication or was
aware of the work it contained could continue to champion the old way of
thinking.
Everything that we
have learned about the solar system, until quite recently, was obtained by
telescopic observation and an analysis of the light from the object being
observed. Consequently, we take a look at the physics of light and the
observational tools used in modern astronomy. We will see how light comes in a
full spectrum of “color” that encompasses much more than just the visual part
that our eyes have evolved to use. We will also see how the light from an
object carries much more information about it than most of you are aware.
However, in the case of the solar system, we have developed a way to learn even
more than we can than by Earth bound telescopic observation. Nowadays, we can
put telescopes in space, or even better, we can obtain even more direct
information about objects in the solar system simply by going there and seeing
them for ourselves
Then
we take a tour of the solar system, emphasizing the similarities and
differences of the objects in it, with the ultimate goal of trying to
understand how it came to be, how it has changed over the years and what its
future is likely to be. We currently believe that the solar system began as a
swirling cloud of gas and dust that collapsed under its own weight, spinning
faster and faster as it did so, ultimately forming a disk-like structure. The central
part of this collapsed nebula became the Sun and the outer swirls and eddies
condensed into planets, asteroids, moons, asteroids and smaller conglomerates
of rock and ice.
The
inner planets grew into small, rocky metallic objects known as terrestrial
planets --- of which the Earth is the archetype. These planets are small
because rock and ice were the only material that could condense out of the
collapsing nebula close to its hot center --- and this material was not very
abundant.
The
outer planets, consisting mostly of rock and “ice” cores surrounded by hydrogen
and helium, grew to enormous size by comparison. This happened because they
formed in the outer regions of the nebula where it was cool enough for ices to
condense --- and the material that makes up ices was more than 20 times more
abundant than rocks and metals. The rapidly accreting icy objects grew large
enough to bind up hydrogen and helium, the most abundant elements in the
universe. Jupiter is the archetype of these planets --- hence they are called
Jovians. Asteroids formed in the gap between the outermost terrestrial planet
and the innermost Jovian. The terrestrial planets have very few moons --- half
of them have none. The Jovians, by comparison, have large numbers of moons.
The very outer
reaches of the solar system, beyond Neptune, the outermost Jovian planet,
consists of the Kuiper belt, a quite sizeable disk-like distribution of small
icy objects that blends into an even larger spherical distribution of icy
objects known as the Oort Cloud. These distributions, serve as the source of
the comets that we occasionally see plunging in towards the Sun from the depths
of the solar system’s outer reaches. They, along with the asteroid belt, also
serve as sources of the meteors that every so often light up our skies at
night, sometimes surviving their fiery passage through the Earth’s atmosphere,
crashing onto the surface as a meteorite.
The bulk of our time in this class will be spent on looking at all of these objects in great detail and building a self-consistent model of the origin of the solar system. In general, the class will be descriptive. Mathematics will be used only a little in lecture and most certainly will not be emphasized. You will have some mathematical problems to solve as part of your homework assignments, particularly the early ones. Later assignments will contain almost now mathematical questions. Mathematical problems on your exams will be almost --- but not completely --- non-existent. The exams are designed to test your understanding of concepts and your ability to recall description --- not your ability to carryout symbolic analysis.
Hopefully, when you are finished
with this class, you will have acquired a strong sense of appreciation not only
for the wonder and awe in which we hold our immediate heavenly neighbors but
how much the study of those neighbors has influenced the development of the
science and culture that has so shaped the inhabitants and environment of the
small, but not insignificant, pale blue dot that we call home.
Check out Carl Sagan's thoughts about astronomy: