the story review: the sky and celestial motion the science

Review

Science andHistory ofAstronomy

Scientific Models

Scientific Method

Models/theories/etc.

The story

The planet problem

Ptolemy

Copernicus

Confidence scale

Tycho

Kepler

Facts and inferences

Today in class

I Review: The Sky and Celestial Motion

I The Science and History of Planetary Motion

Review


Scientific Models

Scientific Method


The story

The planet problem

Ptolemy

Copernicus

Confidence scale

Tycho

Kepler


Review: Celestial Motion

Review


Scientific Models

Scientific Method


The story

The planet problem

Ptolemy

Copernicus

Confidence scale

Tycho

Kepler


Question concepts

Question #1: During a single day or night, the Sun, Moon,stars and planets all appear to move across the sky together.Their relative positions change relatively slowly from night tonight.

Question #2: As the Earth orbits the Sun, the night side ofthe Earth is oriented in a different direction in space, alwaysaway from the Sun. As a result, at different times of yeardifferent constellations are visible in the night sky.

Question #3: Using a figure like that below, where the earthmay be located in various positions around its orbit,characterize the location of constellations in the sky atvarious times (sunset, midnight, noon). For example, theconstellation directly on the opposite side of the earth fromthe sun will be highest in the sky at midnight.

Gemini

Virgo

CancerLeo

Libra

Scorpius

Sagittarius

Capricornus

AquariusPisces

Aries

Taurus

SunEarth

Review


Scientific Models

Scientific Method


The story

The planet problem

Ptolemy

Copernicus

Confidence scale

Tycho

Kepler


Science and History of Astronomy

I Science vs. the scientific method

I Intro to scientific models

I The story of the heliocentric model of the solar system

I More about scientific practice

Review


Scientific Models

Scientific Method


The story

The planet problem

Ptolemy

Copernicus

Confidence scale

Tycho

Kepler


The ancient question, resolved in 1600’s- Apparent Retrograde Planetary Motion

Planets appear to turn around and back up at certain pointsduring their movement among the stars.

Due to the motion of the earth and planets around the Sun.

Review


Scientific Models

Scientific Method


The story

The planet problem

Ptolemy

Copernicus

Confidence scale

Tycho

Kepler


Science vs. the Scientific Method

Science:

I The body of scientific information (facts and inferences)and their confidence levels, relationships

I The community supporting and refining these ideas

The scientific method:

I hypothesize, test, evaluate, refine, repeat

I The process by which ideas are increased (or decreased)in confidence level

Review


Scientific Models

Scientific Method


The story

The planet problem

Ptolemy

Copernicus

Confidence scale

Tycho

Kepler


Scientific model nomenclature

I Models/hypotheses/theories/laws are largely synonymsI example: Kepler’s ”laws” of planetary motion are not

physical laws at all, are observed ”empirical” relationsI Newton’s theory of gravity is incorrect (Einstein’s is

”better”) but we still call it a theory and call itsconstituent principles ”laws.”

I Distinctions are sometimes made in certain cases, butthese are largely contextual

I in this lecture sun-centered solar system is ”hypothesis”even though actually proven fact

I A model can be both ”right” and ”wrong”I Even an incorrect model can continue to have utility

I A model can be ”just wrong”I there are many incorrect models that have no utility

utility = ability to predict outcomes of situations

Review


Scientific Models

Scientific Method


The story

The planet problem

Ptolemy

Copernicus

Confidence scale

Tycho

Kepler


The ancient question, resolved in 1600’s- Apparent Retrograde Planetary Motion

Planets appear to turn around and back up at certain pointsduring their movement among the stars.

Due to the motion of the earth and planets around the Sun.

Review


Scientific Models

Scientific Method


The story

The planet problem

Ptolemy

Copernicus

Confidence scale

Tycho

Kepler


The Models (at this point ”hypotheses”)

Sun-centeredprojection effect

Earth-centeredcircles on circles (epicycles)

Review


Scientific Models

Scientific Method


The story

The planet problem

Ptolemy

Copernicus

Confidence scale

Tycho

Kepler


Ptolemaic model - c. 100Based on ideas developed in ancient Greece

Greeks developed both earth andsun-centered models

Earth-centered model favoredbecause it was thought that theearth must be static

I Stars don’t shift as Earth moves- In fact they do, it is just verysmall (parallax)

I Movement of Earth isinconsistent with motion ofobjects on Earth- In fact, Aristotle’s laws ofmotion were wrong

Provided reasonably accurateprediction

Review


Scientific Models

Scientific Method


The story

The planet problem

Ptolemy

Copernicus

Confidence scale

Tycho

Kepler


Copernican model - 1500’s

Copernicus formalized existingproposal in 1500’s to allow bettercomparison

I He was convinced sun-centeredprovided a simpler explanationfor retrograde motion

I To provide accurate predictionswith circular motions, just ascomplicated as Ptolemaicmodel (circles on circles wereneeded)

I Still concerned about a movingEarth

Review


Scientific Models

Scientific Method


The story

The planet problem

Ptolemy

Copernicus

Confidence scale

Tycho

Kepler


Question concepts

Question #4: A sun-centered solar system had beenconsidered as a possibility since Greek times, even though itwas disfavored until the 1600s.

Question #5: When Copernicus formalized the sun-centeredsolar system, it inferred a different movement in space of theplanets. However, it was not significantly simpler in its initialform, and also the observations of planet motion at the timewere consistent with either the sun- or earth-centered model.

Review


Scientific Models

Scientific Method


The story

The planet problem

Ptolemy

Copernicus

Confidence scale

Tycho

Kepler


Confidence scale

1

10

independent parties

conjecture

measured by multiple

Unlikely speculation

"reasonable" speculation

−1

Disproven

earth-centered had slightly higher

confidence at the time because it was

thought self-evident that the earth wasn’t

moving

The scale of scientific confidence:

I tool to help you categorizescientific ideas

I position of idea on scale candepend on person

I At high levels of confidence,answer is universal

I at lower levels of confidence,scientists can disagree

Experimental evidence (from multiplesources) is given the highest confi-dencedifferent confidence in trustworthyand not trustworthy sources of evi-dence

Review


Scientific Models

Scientific Method


The story

The planet problem

Ptolemy

Copernicus

Confidence scale

Tycho

Kepler


Tycho Brahe - late 1500’s

Realized need for more accurate measurements andperformed them

I In the face of competingtheories which are bothunsatisfactory, gather betterdata!

I This might point the way to atheory better than both

I In this case both Ptolemaic andCopernican models were wrongin detailed comparisons to data

I Shows importance of technicalcapability to advancingscientific understanding

Review


Scientific Models

Scientific Method


The story

The planet problem

Ptolemy

Copernicus

Confidence scale

Tycho

Kepler


Kepler - early 1600’s

By abandoning circles was able to develop a highly accuratesun-centered model

Stated in 3 laws (will be discussed more later)

I Orbits are ellipses

I Equal area in equal time (sets orbital speed)

I Quantitative relation between period and orbit size

Review


Scientific Models

Scientific Method


The story

The planet problem

Ptolemy

Copernicus

Confidence scale

Tycho

Kepler


When Tides Change in Science

The new precision of Tycho’s measurements (facts) made aearth-centered solar system an unlikely inference.

Kepler’s laws, which were sun-centered, provided a morecompelling inference because they were very consistent withTycho’s observations of planet motion in the sky. This drovea historical shift in opinion toward a sun-centered solarsystem.Elevated the confidence of sun-centered model overEarth-centered.

But the motion of the Earth had not been detected (actuallyit wouldn’t be until the 1800’s).

Review


Scientific Models

Scientific Method


The story

The planet problem

Ptolemy

Copernicus

Confidence scale

Tycho

Kepler


Facts and Inferences

Inference can’t have higherconfidence than facts onwhich it is based, and mayhave much lower

1

10

independent parties

conjecture

measured by multiple

Unlikely speculation

"reasonable" speculation

−1

Disproven

Facts:

I observations

I bare results of experiments(what happened)

I line can get blurry for extremelywell tested ”theories”Example: the motion of theplanets in the sky

Inferences:

I often first called ”hypotheses”

I may have very high or lowconfidence

I Example: (historically) themotion of the planets/sun inspace

the story review: the sky and celestial motion the science

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