"General Science Class" According to the professor, what did Kepler do to verify his theory of planetary motion?

Narrator: Listen to part of a discussion in a general science class.
Professor:
Okay, This is a general science course, and as such, the first thing I want you to understand is the  Q46
scientific method. In your book, the definition of the scientific method is "an organized approach to
explaining observed facts, with a model of nature that must be tested, and then modified or discarded if it fails
to pass the tests." So let’s take that apart and talk about it. What are observed facts? Anyone?
Student 1: I’ll try.
Professor: Okay.
Student 1: Isn’t a fact supposed to be a statement that everyone agrees on?
Professor: So you would say that a fact is objectively true.
Student 1: Yeah. That’s what I mean. Professor:
Okay. That sounds good, but what about this... we consider it a fact that the Sun rises each morning
and the Earth rotates. But facts like that are not always agreed upon. Look, when we say that the Sun
rises each morning, we assume that it is the same Sun day after day—an idea that might not have been
accepted by ancient Egyptians, whose mythology taught them that the Sun died with every sunset and
was reborn with every sunrise. Now, let’s consider the case of the Earth’s rotation. Well, for most of
human history, the Earth was assumed to be stationary at the center of the universe. So, as you can  Q47
see, our interpretations of facts often are based on beliefs about the world that others might not share.
Still, facts are the raw material that scientific models seek to explain, so it’s important that scientists
agree on the facts. How can we do that?
Student 2:
How about this... a fact has to be verified, I mean, that’s where the testing comes in, so we have to be
able to test a model, but we have to be able to test a fact, too, right?
Professor:
Now you’re on the right track. In the context of science, a fact must therefore be something that anyone
can verify for himself or herself, at least in principle. So, even though the interpretation may be different,
some interpretation of the Sun is there every morning, and that can be verified. Then, a model is
proposed to explain the facts. And a model is...
Student 3: ... an explanation of the facts.
Professor:
Right. Once the facts have been observed, a model can be proposed to explain them and not only
explain what is obvious but also make predictions that can be tested through further observations or
experiments. Let’s go back to Ptolemy’s model of the universe, which assumed that the Earth was the
center of everything. Okay, that was a useful model because it predicted future locations of the Sun,
Moon, and planets in the sky. However, although the Ptolemaic model remained in use for nearly 1500
years, eventually it became clear that its predictions didn’t quite match actual observations—a key
reason why the Earth-centered model of the universe finally was discarded.
Student 2: So models are discarded when they don’t match the observations.  Q50
Professor:
Exactly. And new models are proposed to explain the facts in a better or more inclusive way. Okay, how
does a model achieve the status of a theory?
Student 1:
Well, I guess sometimes the model doesn’t fail, you know, it gets repeated by many experiments and
the, uh, the uh... pre-um, predictions are verified.
Professor:
So, when a prediction is verified...repeated, then we start to assume that the model is a valid
representation of nature, and when that happens with many experiments and a number of different
researchers, then the model achieves the status of a scientific theory.
Student 2: But...
Professor: Yes? Jerry?
Student 2: Well, the problem is that theories get discarded, too, don’t they? Professor:
Absolutely. Because it isn’t really possible to prove that a theory is true beyond all shadow of a doubt.
And that’s good because doubt is a cornerstone of science. Even a well-researched and presented
theory should undergo continuous challenges from the scientific community, with further observations and
experiments.
Student 3:
I’m sorry. Did we mention the term hypothesis? Does that fit in with a model or a theory?
Professor:
Glad you brought that up. A proposed model is often called a hypothesis, and that just means that the
scientist is making an educated guess that the model’s predictions will bear up under testing.
Student 3: So a hypothesis is a proposed model.  Q48
Professor:
Right. But let’s put this all together, shall we? Step 1 is observation, the collection of data, that is,  
observations. Step 2 is hypothesis or a model to explain the facts and to make predictions. Step 3 is additional
observations and experiments. And here’s the important part, when the predictions fail, then we
recognize that the model is flawed, and we have to revise or discard it, but when the predictions are verified
on a consistent basis, then we consider the possibility that we have a true representation of nature and
we elevate the model to the status of a theory.
Student:So step 4 is the theory?.
Professor:
Right. But, even then, the theory must undergo step 5... that’s further observations, experiments, and
challenges. Okay so far?... Okay. Now for a reality check. In the real world of science, discoveries are
rarely made by a process as... as mechanical as the idealized scientific method outlined in your text-
book... the one that we just summarized. For example, anyone recognize the name Johannes Kepler?
Student 2: Sure. Didn’t he propose the laws of planetary motion?
Professor:
He did, in about 1600. But instead of verifying new predictions on the basis of his model, he tested the  Q49
model against observations that had been made previously. And... and...like most scientific  Q51
discoveries, Kepler’s work involved intuition, collaboration with others, moments of insight, and luck. And
eventually, other scientists made a lot of observations to, uh... verify the planetary positions predicted
by his model.
Student 1: Student 2:
So the...  ...Then
Student 2: Go ahead.
Student 1: So the scientific method in the book... that’s not really the way it happens a lot of the time? Professor:
Okay, let’s put it this way... the scientific method is a process that we need to keep in mind as we do
the work of scientists, but we should also understand that it’s an idealized process for making objective
judgments about whether a proposed model of nature is close to the truth. And we should also keep in
mind that in the work of scientists, other factors are also brought to bear on those ideal steps in the
process.