The
universe.
It is
pretty amazing when you think about it.
Either
that, or you get a major headache.
Personally,
I am in awe when I think about space or anything related to it. Space goes on
forever and ever. The concept of space, in its entirety, is impossible for the
human mind to comprehend. I guess that is what makes it so interesting.
Have you
ever thought about how much you actually know about our solar system? If you are
reading this, you probably know a lot more than you think. Here are some
examples of things you might know about our solar system:
- The planets in our solar system revolve around the sun.
- Each planet has a special orbit.
- The moon revolves around the earth.
- Earth is tilted on its axis.
- When the moon’s orbit overlaps with the sun, here on earth we see an eclipse.
- The stars that are not a part of our solar system are all billions of miles away.
How do you
know all of this? You probably know most of it, if not all of it, because you
were taught in school. You had some sort of Earth Science class that taught you
more about astronomy than you probably cared to know. Have you ever thought
that maybe you are taking this wealth of knowledge for granted?
What? You say. What is this girl talking about?
Would you
like to know? I will tell you, but first ask yourself: If you did not have
science classes that taught you about astronomy, would you know anything about
it? And if not, would you try to understand what was happening beyond your own
town, much less in space?
(In order
to explain a detail of some specific models of the solar system, I am going to
give you some background regarding Aristotle’s physics.)
If you lived
in Aristotle’s time, chances are you would be like the majority of the
population in 360 BC. As you can probably guess, most people at that time were
not particularly interested in astronomy.
Aristotle
was a Greek philosopher and scientist who basically came up with the first
recorded notion of physics. Aristotle believed that there were two regions of
applicability: the celestial sphere and the terrestrial sphere. The celestial
sphere was reserved to all things belonging to heaven, and the terrestrial
sphere was for things that were less than perfect, like the earth. In
Aristotle’s physics, there were five elements. Earth had four of them: air, earth,
fire, and water. And one was in the celestial sphere: quintessence.
In
Aristotle’s physics, everything had a natural state. In the celestial sphere,
the natural state of things were perfect circles. In the terrestrial sphere,
everything was naturally at rest, and everything attracts what it was most
similar to, or made out of.
For
example, you are a human, and you are always on the ground, close to the earth.
Therefore, according to Aristotle’s physics, you are mostly made of earth.
Makes
sense, right? Well, you might be wondering why
Aristotle’s physics were this way. And if you are wondering that, then I
personally applaud you for questioning the theory that stood unshaken for
almost two thousand years. Aristotle’s physics was a guide for scientists for nearly
two thousand years before it was disproven by Galileo Galilei, but that is
another topic entirely.
Now I will
begin with the history of solar system models.
There were
some small models of the solar system that we know were proposed after
Aristotle’s time. However, none of them made an impact quite like Ptolemy’s
model did. In about 100 AD in Rome, Claudius Ptolemy presented his geocentric
model of the universe.
In this
model, the earth was considered the center of the entire universe. Each planet
moved on a small sphere or circle, called an epicycle, that moved on a larger
sphere or circle, called a deferent. There were speculations in the scientific
community, of course, but they were quickly hushed with the added complexities.
Earth was considered to have an eccentricity from the center of the deferent,
which explained many of the patterns they saw in their observations of the
night sky.
About
thirteen thousand years later, in the year 1543, Nicolas Copernicus’
heliocentric model seriously challenged Ptolemy’s long-standing model. After
studying Ptolemy’s model of the solar system, Copernicus found some serious
flaws. The Ptolemaic model could not precisely predict the motion of the
planets, and it kept getting worse over time. It also used huge epicycles to
explain the retrograde motion of the planets. However, when the sun is placed
in the center of the model, it explains the retrograde motion more effectively.
In
Copernicus’ model, the sun was at the center. It is important to understand
that at that time his idea was considered extremely radical. It was widely
accepted that the earth was the center of the universe, and astronomers were
extremely hesitant to consider other models. Copernicus did not publish his
essay with his heliocentric model until the year of his death.
Up to this
point all models had used perfect circles to describe the orbits of the
planets, mostly because of Aristotle’s physics. Heavenly things were naturally
formed in perfect circles, which made sense up to this point in history.
However, our next scientist found something most interesting in his new model
of our solar system.
In about
1600, Johannes Kepler had been studying Copernicus’ heliocentric model, when he
found some interesting discoveries. Mars and Venus were not following the pattern
that they should have been following, according to the Copernican model. After
a lot of studying and record keeping, he came up with his own model.
In the
Kepler solar system model, the orbits of the planets are not perfect circles,
they are ellipses. The sun is not in the exact center, either. The sun is at
one foci of the ellipse. The planets also do not move at the same speed around
the sun. They move faster when they are closer to the sun, and slower when they
are farther away.
This model
of our solar system was fairly accurate, and the larger framework basically
remains unshaken today. Look how far we have come as a society! From the
mystery of how nature works, to the grand scale of our solar system, we
continue this pattern of scientific progress every day.
Now you
know a little more about the history of our solar system, and hopefully you
realize how fortunate you are to know what you do about our place in the
cosmos.