Topicm26669acfae402ef0_1528449000663_0Topic

MotionmotionMotion of the planets on the celestial sphere. The heliocentric system. The development of the Copernican concept

Levelm26669acfae402ef0_1528449084556_0Level

Third

Core curriculumm26669acfae402ef0_1528449076687_0Core curriculum

III. Gravity and elements of astronomy. The student:

4) describes the structure of the Solar System and its place in the Galaxy; uses the concepts of the astronomical unit and the light year.

Timingm26669acfae402ef0_1528449068082_0Timing

45 minutes

General learning objectivesm26669acfae402ef0_1528449523725_0General learning objectives

Describes the features of the heliocentric model.

Key competencesm26669acfae402ef0_1528449552113_0Key competences

1. Lists the differences between a geocentric and heliocentric system.

Operational (detailed) goalsm26669acfae402ef0_1528450430307_0Operational (detailed) goals

The student:

- distinguishes the heliocentric and geocentric model,

- discusses the development of the heliocentric model.

Methodsm26669acfae402ef0_1528449534267_0Methods

1. Discussion.

2. Text analysis.

Forms of workm26669acfae402ef0_1528449514617_0Forms of work

1. Individual work.

2. Group work.

Lesson stages

Introductionm26669acfae402ef0_1528450127855_0Introduction

Students present the state of knowledge about the heliocentric model.

Explain what it means to say about Nicolaus Copernicus that he „stopped the Sun and moved the Earth”.

Procedurem26669acfae402ef0_1528446435040_0Procedure

Our understanding of the Universe has evolved over time.

Most of all the early cosmologic models assumed that the Earth was the centre of the Solar System, and not only this, but of the entire universe.

Aristarchus of Samos proposed the first heliocentric model in the third century B.C., but at this time this model did not play an important role.

[Illustration 1]

The ancient astronomers observed that planets usually moved east to west against the distant stars, but from time to time they changed the direction and the speed. This motion in the opposite direction was called retrograde motion. Nowadays we know that it is an apparent motion.
The Greek astronomer Ptolemy used measurements of the sky to create geocentric model of the Universe. In this model the Earth was at the centre and all the planets and the Sun were orbiting around it. He explained the observed retrograde motion of the planets in such way that each planet moved on a small circle, called an epicycle whose centre moved on a larger circle, called a deferent. The stars revolved on a celestial sphere around the outside of the planetary orbits.
m26669acfae402ef0_1527752256679_0The ancient astronomers observed that planets usually moved east to west against the distant stars, but from time to time they changed the direction and the speed. This motion in the opposite direction was called retrograde motion. Nowadays we know that it is an apparent motion.
The Greek astronomer Ptolemy used measurements of the sky to create geocentric model of the Universe. In this model the Earth was at the centre and all the planets and the Sun were orbiting around it. He explained the observed retrograde motion of the planets in such way that each planet moved on a small circle, called an epicycle whose centre moved on a larger circle, called a deferent. The stars revolved on a celestial sphere around the outside of the planetary orbits.

[Interactive graphics]

The geocentric model was in use over many centuries. In 16Indeks górny th century Nicolaus Copernicus came up with a different model. In 1543, few months before his death Copernicus published his theory in a book: „De revolutionibus orbium coelestium” („On the revolutions of the heavenly bodies”).

Copernicus theory stated that the Sun is at the centre of the system and all planets, including the Earth, revolve around it. This theory is named heliocentric, what means that the Sun is at the centre (“helios” in Greek means “Sun”). In Copernicus theory the Moon is the only celestial body in this system which orbits the Earth, and together with the Earth, they orbit the Sun. The planets orbitorbitorbit the Sun in circular paths modified by epicycles. The planet’s speed is uniform. The theory assumed that the stars are immovable and their apparentapparentapparent daily motionmotionmotion was caused by the daily rotation of the Earth. The retrograde motionretrograde motionretrograde motion of the planets was the result of the Earth’s orbital motion.

[Illustration 2]

Decades later, Johannes Kepler, using very precise data collected by his former mentor Tycho Brahe, found that planets do not move in circles, but in ellipses.

With time, the instruments used by astronomers has been developed and allowed to provide more accurate measurements.

Galileo Galilei was the first astronomer who used a telescope to study the sky. He made a number of observations that finally helped convince people that the heliocentric model was correct. Galileo discovered spots on the Sun and also saw that the surface of the Moon was rough. He discovered that Venus has phases, much like our Moon does.

The heliocentric theoryheliocentric theoryheliocentric theory claimed by Galileo had many opponents and officially was banned for a long time. He was also forced to recant this theory and placed under house arrest for the last eight years of his life.

Few decades later Newton generalized Kepler laws and showed that the planets and the Sun all revolve around the centre‑of‑mass of the Solar System.

Final proof of the heliocentric theoryheliocentric theoryheliocentric theory for the Solar System appeared in 1838, when the first measurement of the distance between a star and the Earth was done. Bessel determined the distance to 61 Cygni by measuring its parallax. His measurements were consistent with orbital motion of the Earth around the Sun.

At present, the knowledge status is such that the Sun is not regarded as a centre of the Universe anymore but a star among many. The Sun lies at the focus of the elliptical orbits of planets revolving around it. And the Solar System is one of thousands of other similar systems in the Universe.

Lesson summarym26669acfae402ef0_1528450119332_0Lesson summary

The heliocentric theory states that the Earth revolves around the Sun. It replaced the geocentric theory which stated that the Earth was the centre of the Universe. The heliocentric theory gave an input for intensive astronomical observations and calculations which are still ongoing.m26669acfae402ef0_1527752263647_0The heliocentric theory states that the Earth revolves around the Sun. It replaced the geocentric theory which stated that the Earth was the centre of the Universe. The heliocentric theory gave an input for intensive astronomical observations and calculations which are still ongoing.

Selected words and expressions used in the lesson plan

apparentapparentapparent

celestial spherecelestial spherecelestial sphere

deferentdeferentdeferent

epicycleepicycleepicycle

geocentric theorygeocentric theorygeocentric theory

heliocentric theoryheliocentric theoryheliocentric theory

motionmotionmotion

orbitorbitorbit

retrograde motionretrograde motionretrograde motion

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motion

ruch

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orbit

orbita

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apparent1
apparent

pozorny

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retrograde motion1
retrograde motion

ruch wsteczny

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heliocentric theory1
heliocentric theory

teoria heliocentryczna

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celestial sphere

sfera niebieska

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deferent

deferent

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epicycle

epicykl

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geocentric theory

teoria geocentryczna

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