Download Physivd Preliminary Module 8.5 The Cosmic Engine

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Module 8.5
The Cosmic
Engine
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
8.5 The Cosmic Engine (30 indicative hours)
Contextual outline
The Universe began with a singularity in space-time. After the initial explosion, the Universe started to
expand, cool and condense, forming matter. As part of this ongoing process the Sun and the Solar System
were formed over 4x109 years ago from a gas cloud which resulted from a supernova explosion. The
condensing gas and dust that formed the Sun and the planets contained all its original elements. The
planets were formed when matter came together under the influence of gravity.
This module increases students’ understanding of the history of physics, implications of physics for society
and the environment and current issues, research and developments in physics.
Assumed Knowledge
Domain: knowledge and understanding:
Refer to the Science Stages 4–5 Syllabus for the following:
5.6.5a identify that energy may be released from the nuclei of atoms
5.7.1a describe the features and location of protons, neutrons and electrons in the atom
5.9.1a discuss current scientific thinking about the origin of the Universe
5.9.1c describe some of the difficulties in obtaining information about the Universe
5.9.3a relate some major features of the Universe to theories about the formation of the Universe
5.9.3b describe some changes that are likely to take place during the life of a star.
Skills
During this module teaching/learning activities should allow time to reflect on the relationships between the
processes involved in the evolution of the Universe, the formation of stars and solar systems and the effects
of solar and terrestrial processes on the Earth. Emphasis must be placed on the evidence for the processes
and the effects that such processes have on the Earth's atmosphere. Skill development relies on teacher
input to model skills that students may need further assistance in refining. The skill development in this
program focuses on:
 Accessing information from a range of resources, including popular scientific journals, digital
technologies and the Internet;
 Developing skills in selection of appropriate media to present information;
 Identify examples of the interconnectedness of ideas or scientific principles;
 Using models, including mathematical ones, to explain phenomena and/or make predictions;
 Analysing information to identify examples of interconnected ideas or scientific principles;
 Summarising and collating information from a range of sources;
 Assess the reliability of first-hand and secondary information and data by considering information from
various sources, and
 Assess the accuracy of scientific information presented in mass media by comparison with similar
information presented in scientific journals.
Values and Attitudes
This module aims to assist students to develop positive attitudes about themselves and positive values
about learning and towards the environment. In addition the module will help students to value ethical
behaviour in the assessment of ideas and the views of others. In particular this module aims to develop in
students:





a desire for critical evaluation of the consequences of the application of physics;
curiosity and critical thinking towards some of the big questions in science;
a tolerance of uncertainty and an acceptance of the provisional and evolving status of scientific
knowledge;
be prepared to make informed judgements;
to value and appreciate physics in becoming scientifically literate persons; and an ability to show
flexibility and responsiveness to ideas and evidence as it arises.
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Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Concept Map
UNIVERSE
Current
Model
Historical
Models
Origin
Expansion
Accretion of
galaxies and
Stars
Radiation
to Matter
Fusion
Reactions
Radioactive
Behaviour
Life-Span
Varieties
of Star
Groups
Life-Span
Emissions
from nuclei
Explosions
(supernovas))
Brightness
and
Luminosity
SOLAR
SYSTEM
Development
and Current
Structure
Newton's Law of
Gravitation
Kepler's
3rd Law
Sun
Emissions
Earth
Sun Spots
Solar Winds
Atmosphere
Black
Bodies
Magnetic Fields
and
Van Allen Belts
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Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
The Cosmic Engine Module Plan
Module Length: 7 weeks
Focus Area
1. Our Sun is just one
star in the galaxy and
ours is just one
galaxy in the
universe
2. The first minutes
of the universe
released energy
which changed to
matter, forming stars
and galaxies
Time
2
½
½
½
2
3. Stars have a
limited life span and
may explode to form
supernovas
2
½
2
3
Concept
Resources
Practical
1. outline the historical
development of models of the
universe from the time of Aristotle
to the time of Newton
Summary notes
1. outline the discovery of the
expansion of the Universe by
Hubble, following its earlier
prediction by Friedmann
2. describe the transformation of
radiation into matter which
followed the ‘Big Bang’
3. identify that Einstein described
the equivalence of energy and
mass
4. outline how the accretion of
galaxies and stars occurred
through:
–expansion and cooling of the
Universe
–subsequent loss of particle
kinetic energy
–gravitational attraction between
particles
–lumpiness of the gas cloud that
then allows gravitational collapse
1. define the relationship between
the temperature of a body and the
dominant wavelength of the
radiation emitted from that body
2. identify that the surface
temperature of a star is related to
its colour
NS: Birth of the
Universe
Contexts I: pp.
299-312
1. (Act 1) identify data sources,
gather, process and analyse
information to assess one of the
models of the Universe developed
from the time of Aristotle to the time
of Newton to identify limitations
placed on the development of each
model by the technology available
at the time
2. (Act 2) identify data sources and
gather secondary information to
describe the probable origins of the
universe
3. describe a HertzsprungRussell diagram as the graph of a
star’s luminosity against its colour
or surface temperature
4. identify energy sources
characteristic of each star group,
including Main Sequence, red
giants, and white dwarfs
NS: Life of a Star
WS: HR Diagrams
NS: A Theory of
Some Gravity
WS: Boltzmann
Distribution
1. (Act 3) gather secondary
information to relate brightness of
an object to its luminosity and
distance
Contexts I: pp.
313-324
NS: Rocky Dwarfs
and Gassy Giants
Contexts I: pp.
318-320
2. (Act 4) process and analyse
information using the HertzsprungRussell diagram to examine the
variety of star groups, including
Main Sequence, red giants, and
white dwarfs
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Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Focus Area
4. The Sun is typical
star, emitting
electromagnetic
radiation and
particles that
influence the Earth.
Time
1
2
Concept
Resources
Practical
1. identify that energy may be
released from the nuclei of atoms
Contexts I: pp.
320-322
2. describe the nature of
emissions from the nuclei of
atoms as radiation of alpha and
beta particles and gamma rays in
terms of:
- ionizing power
- penetrating power
- effect of magnetic field
- effect of electric field
3. identify the nature of emissions
reaching the Earth from the Sun
4. describe the particulate nature
of solar winds
5. describe sunspots as
representing regions of strong
magnetic activity and lower
temperature
Contexts I: pp. 362
Humphrey Set 76
1. (Act 5) present information and
use available evidence to discuss
the factors affecting the size of the
gravitational force
2. (Exp 6) perform a first-hand
investigation to gather information to
compare the penetrating power of
alpha, beta and gamma radiation in
a range of materials.
Contexts I: pp.
346-360
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Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Assumed Knowledge from Years 7 - 10 Science:
Domain
4.6 identifies and
describes energy
changes and the
action of forces in
common
situations.
5.6 applies basic
physical models,
theories and laws
to situations
involving energy,
force and motion.
4.9 describes the
dynamic structure
of Earth and its
relationship to
other parts of our
solar systems
5.9 relates the
development of
the universe and
the dynamic
structure of Earth
to models,
theories and laws
and the influence
of time.
Stage 4 (Years 7-8)
4.6.10 gravitational force to:
a) identify that all objects exert a force of gravity on all other objects in the
universe,
 State that mass is the amount of material in an object.
 Define the unit of mass as the kilogram (kg) and is measured using a
mass balance.
 State that gravity is a force that acts on the mass of an object to give
the object “weight”
 Describe how the weight of an object can change from planet to planet
while its mass will stay the same.
describe characteristics of specific forces in terms of size and direction
describe and use quantitatively the relationship between force, mass and
acceleration
apply Newton's laws to space travel
discuss the life, times and achievements of Newton
describe the used of magnetised materials in everyday situations.
4.9.1 the Newtonian model of the solar system to:
a) describe qualitatively relative sizes, distances and movements of
components of our solar system
 State the order of the planets in our solar system
 Explain the difference between dust, micrometeors, meteors,
asteroids, comets, planetismals and planets in terms of size and
composition.
 Distinguish between the rocky planets (Mercury, Venus, Earth, Mars,
Pluto) and the gas giants (Jupiter, Saturn, Uranus, Neptune) in terms of
composition and size.
 Define the ecliptic plane as the imaginary plane that most planets orbit
in
b) describe relative movements of the planets, moons and sun
 Explain why the Sun appears stationary to the other components of the
solar system owing to its large mass compared to the rest of the
material in the solar system.
 State that planets orbit a sun.
 State that asteroids and comets also orbit the Sun but in an irregular
way.
 State that moons orbit a planet.
c) explain night and day in terms of Earth’s rotation
Stage 5 (Years 9-10)
5.6.6 gravitational force to:
a) distinguish between the terms ‘mass’ and ‘weight’.
 State that mass is the amount of material in an object while
weight is the force of gravity on that mass.
 State that, at the Earth’s surface, the acceleration due to gravity is
9.81 m/s2
relate qualitatively the force of gravity between two objects to their
masses and distance apart.
5.9.1 the big bang theory to:
a) discuss current scientific thinking about the origin of the universe
 Describe the big bang theory and its estimate of the age of the
universe.
 Explain how Hubble postulated the expansion of the universe that
led to the big bang theory.
b) identify that some types of electromagnetic radiation are used to
provide information about the universe.
 Describe the operation of and information obtained from the
following devices:
 Radio telescopes
 Microwave satellites
 Infra-red satellites
 Visible telescopes (both ground-based and space)
 UV satellites
 X-ray satellites
 Gamma ray satellites.
c) describe some of the difficulties in obtaining information about the
universe
 identify wavebands in the EM spectrum that are absorbed by the
atmosphere or interfered by human activities.
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Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Domain
Stage 4 (Years 7-8)
 State that the Earth rotates about its axis (optional: define sidereal day
as 23 h 56 m and explain why it is different to a solar day)
 Explain how the earth presents only approximately half of its area to
the Sun at any one time.
 Describe dawn and dusk as times where the Earth is in the edge of the
shadow of the Sun using diagrams.
d) explain the seasons in terms of the tilt of Earth’s axis and its revolution
around the sun.
 Define axial tilt as the angle between the planet’s spinning axis and the
perpendicular to the Sun.
 Define an equinox a day with equal night and day (12 hours each) and
use diagrams to explain when the two equinoxes occur (vernal and
autumnal)
 Define the term solstice as a day with the longest night/day and use
diagrams to explain when the summer and winter solstice occur.
 Explain why the equator receives the most light and the amount of light
reduces going to higher latitudes using diagrams.
relate the model of the solar system to the observed sky
examine information collected to assist in predicting events such as
appearances of comets, eclipses and other solar system phenomena.\
collate information gained from planetary research to support theories on
the formation of the solar system.
compare the planetary geology found within the solar system.
research the historical development of the present model of the solar
system, including the work of Copernicus, Galileo, Kepler and Newton.
4.9.2 components of the universe to:
a) describe some major features of the universe, including galaxies, stars,
nebulae and solar systems.
 Describe stars, solar systems, nebulae, galaxies and clusters in terms
of size, composition and number of components
 Classify galaxies according to shape:
 Globular
 Elliptical
 Spiral
 Barred
b) use appropriate scales to describe differences in sizes of, and distances
between, structures making up the universe
 Use a scale of 1mm is the width of a solar system to describe galaxies
and clusters.
 Use a scale of 1mm is the width of the Moon to describe scales within
the solar system.
Stage 5 (Years 9-10)
 Explain why particulate material from space is hard to measure
due to interference from the Solar wind.
compare the big bang theory with other theories of the development of
the universe
consider interactions between various features of the universe and
hypotheses on past and future developments in the universe
investigate ways in which different societies have described changes
in the universe
describe evidence used to support estimates of time in the universe.
5.9.3 components of the universe to:
a) relate some major features of the of the universe.
 Describe stars, solar systems, nebulae, galaxies and clusters in
terms of size, composition and number of components
 Classify galaxies according to shape:
 Globular
 Elliptical
 Spiral
 Barred
b) describe some changes that are likely to take place during the life
of a star.
 State that the life path a star takes depends on its mass.
 Briefly describe the main stages and time spent in each stage in a
star’s life for the following masses:
 <0.1: formation of brown dwarf
 0.5-2: protostar  t-tauri  main sequence  red giant 
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Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Domain
Stage 4 (Years 7-8)
explain how different cultures have interpreted constellations.
compare time scales used to describe features in the solar system,
including orbits of moons and planets.
Stage 5 (Years 9-10)
variable  novae  white dwarf
 >5: protostar  main sequence (blue/white supergiant) 
supernova  neutron star/black hole.
relate colours of stars to their age, distance from Earth and size
explain why quasars have provided evidence of a changing universe
discuss the impact of Voyager probes and the Hubble Space
Telescope on knowledge and understanding of the universe
4.9.4 the atmosphere to:
a) identify gases that comprise the greater percentage of air and explain
the difference between atmosphere and space
 Describe space as a volume where there are relatively few gas
particles.
 Describe how the density of air changes as the altitude increases.
 Give the official definition of where the atmosphere ends and space
begins.
 Create a pie chart of the major gases in the atmosphere: nitrogen,
oxygen, (water), carbon dioxide.
b) describe the importance of atmospheric gases, including ozone and
greenhouse gases, to life on Earth
 Describe ozone as another, hazardous form of oxygen.
 State that ozone is produced by electrical discharges such as lightning
storms.
 Describe how the ozone layer forms.
 Explain how the ozone layer protects the surface of the Earth from UV
 Describe how some chemicals such as CFCs destroy ozone, forming
ozone “holes” in the ozone layer.
 Explain how some gases such as water, carbon dioxide and methane
trap/reflect heat escaping from the earth’s surface.
 Describe the greenhouse effect as the action of these gases to keep
the Earth’s surface warm.
 Explain that an enhanced greenhouse effect to due to the addition of
extra amounts of greenhouse gases due to human activities, identifying
the source of each type of greenhouse gas both natural and human.
discuss some methods used to obtain information about changes in the
atmosphere.
relate changes in atmospheric conditions to weather phenomena and
energy transfer processes
describe the history and application of the idea of air pressure.
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Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Preliminary Physics C5 The Cosmic Engine Activity 1: Historical Astronomy
Some Ideas of the Ancients concerning the Nature of the Universe
Babylonians and Egyptians (< 1000 B.C)
 Celestial bodies were living beings (eg Ra was the Sun god)
 The earth was hollow
Early Greek Philosophers
Thales of Miletus (640-546 BC)
The earth was a disc floating on a vast body of water
Anaximander (611-547 BC)
The earth was a free floating cylinder in space
The heavens formed sphere about the earth
The moon was self-luminous
ie the earth is the unsupported centre of the universe
Pythagoras (580-500 BC)
The earth is spherical and surrounded by eight giant transparent concentric spheres that bore all the objects
in the sky. The spheres revolved around the earth on different axes at different uniform speeds. This very
roughly explained the diurnal motion of the fixed stars, sun, moon and the five “wandering stars” (planets).
Problem: The model could not account for:
 The retrograde motion of the planets
 The variation in the apparent size and brightness of the sun and the planets.
Philolaus (a pythagorean)
Proposed the first non-geocentric theory of the universe. The earth was just one of ten celestial objects
orbiting a central “fire”, which was always obscured from view by the “antricthon” (counter-earth). The ten
celestial objects was the sun, moon, earth and 5 other planets, stars and the antricthon, and these all orbited
the central fire.
The significance of this idea is that the earth is just one planet in orbit
Anaxagoras (500-428 BC)
The earth was flat. The sun was molten iron (The reason for this conclusion was that in 467 BC a meteor
fell – supposedly a piece of the sun)
Plato (427-347 BC)
All the diurnal motions are due to the axial rotation of the earth. The stars were living, eternal, unchanging
beings moving with uniform speed in endless circles.
Problem: How can the retrograde motion of the planets be reconciled with Plato’s idea of the nature of
stars?
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Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
The problem of Celestial Mechanics as formulated by Plato:
“What combination of uniform circular motions can account for the apparent retrograde motions of the
planets?”
The solution to this problem, based on Plato’s preconceived ideas concerning the nature of celestial objects,
was to occupy the thoughts of astronomers for the next 2000 years!
Eudoxus (c. 408-355 BC)
Conceived the first comprehensive geocentric system to Plato’s
problem. The universe consisted of celestial objects each on the
equator of an imaginary sphere which rotated with uniform circular
motion. Altogether there were 27 transparent, concentric spheres
rotating uniformly about the earth on various axes not parallel to one
another:
Celestial Object
Sun
Moon
Five planets
Stars
Total
No. of axes /
spheres
3
3
4 each
1
27
Thus the observed motions of the planets and other celestial objects
could (almost) be duplicated by 27 simultaneous uniform circular motions.
Aristotle (384-322 BC)
Made little contribution to astronomy himself but summarised the prevailing astronomical thought. His
writings were important because his physical and astronomical ideas became incorporated into medieval
Christian doctrine, and therefore influenced scientific thought for many centuries.
Aristotle taught that the circle and the sphere were “perfect” figures and were the only ones upon which the
universe could be modelled. He refined and extended the geocentric model of Eudoxus. In Eudoxus’
system, the spheres were simply mathematical constructions. Aristotle replaced them by physically real
crystalline spheres. Aristotle extended the number of spheres from 27 to 55:
1 for the stars
7 each for Saturn and Jupiter
8 each for Mars, Venus and Mercury
7 for the sun
3 for the moon
+6 additional spheres introduced by Callipus (370-300 BC)
Each sphere was driven around by the sphere outside it. The earth was stationary because there was no
observed stellar parallax. Aristotle discussed the possibility of a heliocentric model but dismissed it on this
point. He also taught that the moon was not self-luminous but shone by reflecting light from the sun.
Problem: The model could not explain the periodic changes in the apparent size and brightness of the sun,
moon and planets.
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Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Heraclides (388-315 BC)
Proposed that the universe was infinite and the planets were separate worlds. Mercury and Venus orbit the
sun (This could account for their limited elongations during their retrograde motions).
Aristarchus of Samos (312-230 BC)
Conceived the first heliocentric model in which the earth and all the planets orbited the sun. He was the first
astronomer to attempt measuring the distances of the moon and the sun from the earth.
Eratosthenes (276-194 BC)
Measured the diameter of the earth! The difference in the noon altitude of the sun between Syrene and
Alexandria on June 21 (the summer equinox in the Northern hemisphere) was approximately 7 degrees,
which is about 1/50 of 360. This is also the angle subtended at the earth’s centre circumference of the
earth must be approximately 50 times the distance between these two cities. The distance between the cities
was 5000 stadia1 (1800 km)
x  (90          

A
S 

(  
Thus AS 
2 Re
360

2 Re  AS ( 360 )
 
Re
Re
x
Appolonius
Explained the apparent changes in the size and brightness of the sun, moon and planets by having them
move on eccentric circles about the earth.
Hipparchus (fl. 150 AD)
Carried out careful and precise observations that yielded the
data on planetary positions used later by Ptolemy in the
development of his geocentric theory of the universe. He
proved that an eccentric circle was equivalent to an earthcentred rotating anti-clockwise, coupled with a deferent
centred epic(ycle) rotating clockwise and with the same
period. He also discovered that the vernal equinox drifted
slowly westward along the ecliptic relative to the
background of fixed stars.
One Stadia is approximately 157 metres according to historians, but whether this is the true figure or “reverse engineering” by
historians from Eratosthenes work is a matter of conjecture. Another measure of the stadia gives 197 metres as the current figure
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Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Claudius Ptolemy (c. 150 AD)
Chaos followed the decline of the Greek city states. Most of the ancient world’s intellectual life then shifted
to Alexandria in Egypt. There in the second century AD Claudius Ptolemaeus compiled an encyclopedic
summary of the Greek’s effort to explain the motions of the stars and the planets in his book the “Almagest”
(ie ‘the Greatest of Books”).
The Almagest was a codification of all the then known astronomical treatises and observations (one of the
few books that survived the burning of the great library at Alexandria by the Ottomans).
Ptolemy’s theory:
1. was consistent with both the presuppositions of his day and with the observations that had been made
over the centuries. This made it complex (which was a disadvantage)
2. was moderately successful in predicting the future positions of the planets as well as explaining how they
had appeared in the past. This made it useful.
3. was later fitted into Thomas Aquinas’s widely accepted synthesis of Aristotlean physics and Christian
belief. This made it both intellectually and morally “acceptable”.
The Details of Ptolemy’s Theory
1 The theory was a geocentric model of the solar system.
2 The model was an empirical one ie based on observations
3 The model was based on three geometric devices:
A the eccentric circle: this explained the annual variation in the size of the Sun.
B. defferents and epicycles: these explained the parents of retrograde motion of planets, the
variations in the rate of motions of planets during retrograde motion, the variations in the
brightness of the planets during retrograde motion and the occurrence of eclipses.
C. Equants: these explained the variations in the sizes and durations of the retrograde motions
exhibited by the one planet.
The use of these geometric devices allowed Ptolemy
adhere to the dictums of Plato and Aristotle that the
motions of celestial objects should be uniform
circular motions, and yet still be consistent with
observation. Ptolemy simply introduced circular
motions that when non-concentric, and which were
neither centred on nor uniform about the Earth. The
resulting geometrical analysis was equivalent
defining a complicated equation of motion for each
individual planet. The fact that the overall motion of
the planets was centred on the Earth, while the earth
itself was stationary (ie geocentric) hand
commonsense appeal and also accounted for the
absence of any observed stellar parallax.
to
The inadequacies of Ptolemy’s Geocentric model
1. The model was based on Plato’s philosophical
notion that celestial objects had divine significance and therefore by their nature had to move uniformly
imperfect circles about some centre.
2. It predicted larger variations in the moon’s apparent diameter than is observed
3. It provided no information about the absolute sizes of planetary orbits. It simply gave the relative sizes
of epicycles to deferents.
4. The model was very complex.
5. The model was not exact.
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Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Nicolaus Copernicus (1473 – 1543)
In 1510 Copernicus circulated to a few friends a manuscript, the Commentatiolus, in which he set forth his
beliefs concerning the universe:
1. The theory was a heliocentric model of the universe.
2. The model was a theoretical one: it amounted basically to a change in frame of reference from that of the
Earth to that of the Sun
3. The model was based on the following axioms:
A No one precise geometric centre of all celestial circular motion is exists
B. The Earth is not the station centre of the universe, but only of the moon’s orbit and of terrestrial
gravity.
C. The sun is the centre of the planet the system and therefore of the universe.
D. Apparent diurnal motions are due to the Earth’s diurnal motion on its own axis.
E. The apparent annual motion of the Sun is due to the best annual orbit about the Sun.
F. The apparent retrograde motions of the planets is due to the fact that the Earth and all the planets
revolve about the Sun. Hence, when the motion of the planet is viewed from the Earth the
motion of the planet does not appear circular.
G.Compared to the distance of the fixed stars, the earth’s distance from the Sun is negligently small.
Advantages of Copernicus’s model
1. Copernicus was able to use his model to calculate the
period of each planet’s orbit about the Sun, and
predicted that the larger the planets distance from the
Sun the larger its period of orbit.
2. Copernicus was able to use his model to calculate the
relative size of the planets orbit with respect to that of
Earth’s.
3. The model was a geometrically simpler kinematic
solution to the problem first posed by Plato. This made
it more compelling an aesthetically pleasing.
Inadequacies of Copernicus’s Heliocentric model
1. The model offered no clear scientific advantage over
Ptolemy’s Geocentric model. It was simply a change
in frame of reference.
2. To explain the detailed motions of the planets many small epicyclic motions were still needed.
3. No annual stellar parallax was observed, and the fact that the distance of the fixed stars from the earth
was extremely large was simply taken as an axiom and not proved.
4. The model conflict with basic principles of Aristotlean physics which were adhered to by most scholars
of the time.
5. The model conflicted with theological views of the time.
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Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Johannes Kepler (1571 – 1630)
In 1597 Johannes Kepler published his book The Cosmic Mystery in which he showed a unity between
geometry and scientific observation. Kepler sought to solve the puzzle of why there were exactly six planets
and why they were placed at their giving distances from the Sun. His solution was that God the great
geometer had ordained that the spherical shells containing the planetary orbits was faced according to the
shapes of the five regular solids, and that there were only six planets because there were only five regular
solids (with the Earth at the centre).
Although this idea was never accepted his imagination and computational ability brought into the attention
of major scientists such as Galileo & Tycho. As a result, Kepler was invited to become one of Tycho’s
assistants and his new Observatory in Prague in 1600. There Kepler was given the extremely difficult task
of determining in precise detail the orbit of the planet Mars. Kepler eventually solved this problem and in
doing so redirected the course of the study of celestial mechanics.
Kepler’s heliocentric model of the solar system
1. Kepler proposed heliocentric model of the solar system
2. The model was an empirical one based on the very accurate data compiled over 38 years by Tyco Brahe.
3. The model was quantitative and can be summarised by Kepler’s three laws:
A.
Law of Orbits: the orbit of a planet is an ellipse with the sun at one of the foci.
R
Centre
B.
C.
4
R1
R2
foci
planet
Sun
Law of areas: a line joining the planet and the sun suites out of equal area in equal intervals of
time.
2
Law of periods: T 3  const. , Rav = ½ (Ra + Rp)
Rav
Kepler also said that the orbits of the nonterrestrial planets lay in planes inclined at various angles
against the ecliptic.
14
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Significance of Kepler’s work
1. The law of orbits describe the shape of a planet’s orbit and was an abandonment of Plato’s dictum that
planets had to move in circular orbits.
2. The law of areas describe how planet moved in its orbit: a planet moves non-uniformly in its elliptical
orbit. This was also an abandonment of the ancient dictum that planet kept moving uniformly in its
circular orbit.
3. The law of periods described the relationship between different orbits.
4. Kepler’s laws allow the motion of the planet to be completely characterised by six orbital parameters:
Ra
1
Rp
c
e
: eccentricity  
a Ra
1
Rp
Rav : average orbital radius

: argument of the ascending node

: argument of the perihelion
i
: inclination of the orbital plane to the ecliptic

: a date of perihelion passage
5. With the six parameters the past and future history of
each planet could be very accurately derived or predicted.
6. Kepler’s methodology greatly influenced science as it helped establish the use of the algebraic equation
as a form for setting physical laws.
7. Kepler was also the first person to attempt to describe the geometric motion of the planets as being due
to some physical cause: he proposed that the planets were driven around their orbits by a motive force
which emanate from the Sun which diminished in strength with increasing distance from the Sun:
“I am much occupied with investigation of physical causes. My aim in this is to show that the celestial machine is to be likened not to a
divine organism but rather to a clockwork insofar as nearly all the manifold movements and carried out by means of a single quite simple
magnetic force, as in the case of a clockwork, all motions at caused by a simple weight. Moreover, I show how this physical conception
is to be presented through calculation and geometry.” (Letter to Herwart, 1605)
Planet
Mercury
Venus
Earth
Mars
Jupiter
Saturn
Uranus
Neptune
Pluto
R (astronomical units*)
0.387
0.723
1.000
1.523
5.202
9.554
19.218
30.109
39.60
T (seconds)
7.60 X 106
1.94 X 107
3.16 X 107
5.94 X 107
3.74 X 108
9.30 X 108
2.66 X 109
5.20 X 109
7.82 X 109
R3 / T2
0.998 X 1013
0.995 X 1013
1.00 X 1013
0.996 X 1013
0.994 X 1013
0.990 X 1013
1.00 X 1013
0.990 X 1013
0.985 X 1013
* one astronomical unit (AU) is the one-half the sum of the longest
shortest distance from earth to the Sun. 1 A.U = 1.495 X 1014 m
and
15
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Cepheid Variables
This class of stellar objects fluctuate in their apparent luminosity. In essence they are really super giant yellow
stars. They can be classed into two main groups:
a) Irregular Variables
These Cepheids have no regular periodicity to their luminosity but appear to fluctuate randomly
(although these apparent random fluctuations can be in part predicted by chaos theory).
b) Regular Variables
These Cepheids do have a regular period with
which their luminosity varies. The first identified
regular variable was -Cephus (found in the
Magellanic Cloud) with a period of 6½ days.
Modern theories suggest that this periodicity
changes as the age of the star increases and indeed,
some regular variables are hypothesised to become
irregular variables at some stage in their evolution.
Figure 1: Change in Brightness of -Cephus
with time.
If you plotted all the regular Cepheids on a
logarithmic graph, then a linear relationship is
observed. The general trend that is shown is that, as
the Cepheid variable gets larger, its period increases.
It is interesting to note that most, if not all, of the
large Cepheid variables are very distant from the
Earth. Those relatively close to the Earth tend to be
the smaller (and hence shorter period) variables. This
distribution has been incorporated into many of
Figure 2 Plot of Apparent Brightness vs Period theories of the origins of the universe.
for Regular Cepheid Variables
Thus, by measuring the period of a Cepheid you
can determine how far away it is from Earth.
16
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Star Magnitudes
Magnitudes are a logarithmic scale (or rank) system that is used to classify stars according to their brightness.
One of the oldest systems was developed by the Greeks about 2500 years ago. It involved using naked eye
observations of the relative brightness of stars. These stars brightnesses fell into different categories: each
category was separated by being half as bright as the previous, viz.
Group 0 Stars - the brightest in the (Northern) sky.
Group 1 Stars - half as bright as Group 0 stars.
Group 2 Stars - half as bright as Group 1 stars
(quarter as bright as Group 0)
etc.
Group 5 Stars - 1/64 as bright as Group 0 stars
(these are just visible to the naked eye)
This system works adequately for most stars but as our knowledge of stars grew, various problems were
encountered. For instance, some stars in the Southern hemisphere are brighter than those in the Northern
hemisphere, thus a system of negative numbers was needed to accommodate these stars. Secondly, the base 2
aspect of this system proves hard to manage in any mathematical treatment of star magnitudes.
The modern system incorporates the essence of the Greek system with a few changes. Firstly, it was decided
to use five scale divisions which corresponded to a 100 fold change in brightness, viz.
Group -1.4 - brightest stars (includes Sirius)
Group -1
Group 0 - brightest star in Northern hemisphere
Group 1
Group 2 100 fold
each scale division
Group 3 change in OR
is 5100 = 2.51 times
Group 4 brightness
less bright than the
Group 5
one above it.
The brightness of a star depends on several factors. Generally, the larger the star, the brighter it appears
although this is not always the case. Secondly, the surface temperature of the star dictates not only the apparent
brightness but also the colour of the star (see below). Due to the way we perceive colour and the brightnesses of
each colour, this will also influence the brightness of the star to a human observer. Another obvious factor is
how far away the star is from Earth as light intensity follows an inverse-square law for distance. The brightness
of a star as viewed from Earth is called the apparent magnitude.
The absolute magnitude of a star is a calculated value which measures the brightness of a star as it would
appear if it was 10 parsecs away from Earth/observer. This gives a scale that we can compare different stars to
and relate their magnitudes.
e.g. A star has an apparent magnitude m = -1 and absolute magnitude M = 10. What can you determine about
it?
ANS: 1) it is a dim, rather cool star.
2) it is very close to Earth
e.g.2 Another star has m = 8 and M = -2. What can you determine about it?
ANS: 1) it is a very bright star
2) it is a long way away from Earth.
17
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Clearly, by knowing m and M you can judge the distance to a star and its relative surface temperature. But
what is the mathematical relationship between m and M? Well, as we have seen before, the brightness of an
object diminishes according to the square of the distance, hence we can deduce a formula:
Apparent Magnitude m = Absolute Magnitude M X 1/d²
OR
m / M = 1 / d² . . . . . . . (1)
However, magnitudes are an inverse log scale (i.e. as the magnitude number increases, the brightness decreases
on a logarithmic scale). So we can rewrite the formula as thus:
m / M = 2.51 X log10 (d² / 1). . . . . (2)
└this is the difference between two
consecutive magnitude i.e. 5
As the absolute magnitude is defined at a distance of 10 parsecs, we can write the formula as follows:
m / M = 2.51 X log10 (d / 10)²
OR m - M = 2.51 X log10 (d / 10)²
m - M = 5.02 X log10 (d / 10). . . . . (3)
where d is in parsecs
example: For the Sun: m = -27, M = +5
thus m - M = 5 log10 (d / 10)
-27- 5 = 5 log10 (d / 10)
-32 = 5 log10 (d / 10)
-6.4 = log10 (d / 10)
d / 10 = 3 X 10-6
d = 3 X 10-5 parsecs
If a star was 100 parsecs away,
m - M = 5 log10 (100 / 10)
= 5 log10 10
=5
thus the difference between apparent and absolute magnitude would be 5.
Knowing this magnitude formula we can establish a "yardstick" by which to measure relative distances in the
universe. The best (and chosen) stellar objects to do this with are the Cepheid variables, which act as "standard
candles" to which all other measurements are compared.
18
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Spectra of Elements
When we look at the spectrum produced by a typical star, we notice that there are particular wavelengths in
the spectrum which are either missing or reinforced. These wavelengths are directly attributable to the elements
in that star.
When energy is supplied to an atom, it causes electrons in the shell of the atom to "jump" to a higher shell of
the atom. Upon jumping down from this higher energy shell, the electron releases energy, but the amount of
energy it releases is fixed. This energy manifests itself as light of a particular frequency, as given by the
equation E = h.f (see above). Since each element of the Periodic table has its unique shell structure, the energies
involved are also unique to that element. The areas of a spectrum where these transitions occur are called
spectral lines.
Spectral lines can occur in two ways. Firstly, the energy around the atom will cause it to produce spectral lines
and so reinforce those particular spectral lines in the spectrum. This is called emission spectra. The other way
spectra are produced is when the element absorbs those particular frequencies from the surrounding light,
causing a dark band where that frequency used to be. Such a spectrum is called an absorption spectrum.
19
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Black-Body Radiation
In order to understand something about the colour of stars we must visit some ideas that were established last
century. Firstly one must accept that the energy delivered by a single photon (particle) of light is given by the
formula:
Energy E (Joules) = h.f (frequency Hz)
where h is Planck's Constant = 6.62618 X 10-34 Js-1.
This means that higher frequency (hence shorter wavelength) light contains more energy. For the visible
spectrum, red has the least energy and violet has the most.
Secondly, many objects, including stars, can be thought of as a black box (body) with a tiny hole in it through
which the radiation can escape. Normally such bodies will radiate out light at all frequencies but not equally.
The distribution of frequencies depends on the temperature of the box. viz.
It is common experience that the hotter an object
gets, the more blue tends to be the light that it emits.
Consider a stove element. When it is reasonably cool
it emits a dull red glow. As it gets hotter the glow
changes from red through to orange to perhaps even
yellow. Other materials can continue to go through
the spectrum of colours as they get hotter until they
start emitting all the colours (which we perceive as
white light).
It is important to note that even at low temperatures
an object can still emit high energy light but the
proportion of this light is small compared to the other
lower energy forms of light.
Hence red stars are comparatively cooler than
yellow stars which are in turn cooler than white stars
while blue stars are the hottest objects that we can
detect.
Although for the last few thousand years we have Figure 3 - Black-Body Radiation at Different
used visible light to detect the stars, many stellar Temperatures
object radiate energy from the radio wavelengths
(lowest energy) through to cosmic rays (which are above gamma rays in energy), and it is only this century that
we have been able to detect these radiations which are invisible to us. For instance, even though we cannot "see"
a black hole, as matter is dragged into it enormous amounts of energy are released in the X-ray region of light
which we can detect using X-ray telescopes (like the one which was put into orbit in 1990).
20
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Spectral Class
Spectral Type
O
Absolute Magnitude
-6 to –4
Typical Star
-Orion
O5
Surface Temp (K)
30000+
B
-4 to 0
-Orion
B0
28000 to 10000
A
0.5 to 2.5
Vega
A0
10000 to 7500
F
2.6 to 4.3
-Persei
F5
7500-6000
G
4.4 to 5.8
Sun (Sol)
G4
6000-5000
K
5.9 to 8.9
Arcturus
K2
5000-3500
M
9 to 16
3500
W
WC / WN
S
R /N
-6 to –4
-5.3 to –4.7
-1
>16
Antares
(giant)
M1
Rare
30000+
23000 to 28000
2500
<2500
Criteria
Neutral & ionised Helium, HeI
& HeII, ionised carbon CII,
ionised silicon SiIII, After O5,
classification based on HeI4471
/ HeII4541
Weak HeII, disappears at B5;
intense HeI, max. at B2; lines of
OII & NII, H becomes most
intense
HeI disappears; H very intense,
max. from A0 to A3; CaII, FeII,
CrII &TiII, FeI, CrI increase
from A0 to A9. Classification
based on the ratio of CaII3934 H
For
many
stars
strong
pecularities (eg intense bands of
Si or Eu)
Spectrum dominated by many
lines of neutral or singly ionised
metals. CaI most intense. H
rapidly decreases from F0 to F9.
CaII increases. Classification
based on ratio of HI4341 /
CaI4226
Neutral
metals
dominate
spectrum.
Classification on
HI4341 / FeI4325. Bands of
molecular CN and CH appear.
Neutral metals still intense.
Classified on ratio of CaI4226 /
FeI4290+; band of CH@4300.
CN & CH increase. TiO appears
at K5
Many metallic bands.
TiO
dominates.
Many molecules
present.
HeII in emission
CII, CIII, CIV, OII, NIV, NV
No TiO, abundant ZrO
CH, C2, CN
21
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
The Hertzsprung-Russell Diagram
By plotting the absolute magnitude of a star versus its spectral class (or surface temperature) some trends are
evident about the distribution of stars in space.
Most stars fit along a "main sequence" - a continuous series of stars showing a progressive loss of mass and
lower surface temperature. Below 3000C stars are too cool to be luminous.
22
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Galileo Galilei (1564 – 1642)
1. Constructed a refracting telescope and used to obtain direct visual evidence supporting is a heliocentric
theory of Copernicus.
2. He discovered that the moon is pitted and cratered and that the Sun has sunspots. This was contrary to
the Aristotlean dictum that the heavenly bodies were perfect and without such blemishes.
3. He also discovered that the Sun rotating about its own axis and used the sunspots to determine its
rotational period.
4. He observed that Jupiter had four satellites. This provided further evidence that the earth was not the
centre of the solar system. He also observed that the rotational periods of the satellites increased with the
distance from Jupiter, which was in accordance with Kepler’s third Law, although Galileo never
mentioned Kepler’s Law.
5. He observed that the planet Venus showed phases, like the moon. This was direct evidence that Venus
must orbit the Sun.
Some of Galileo’s publications:
The Starry Messenger (??) in which he reports his observations of the moon.
Letters on the Solar Spots (1612)
Letters Concerning the Use of Biblical Quotations in Matters of Science (1615): this was to support
Copernicus viewpoint.
Dialogue Concerning the Two Chief World Systems (1632) Ptolemaic & Copernican
The Assayer (1623) explain the motions of comets
Isaac Newton (1642 – 1727)
When Kepler was searching for the curves that would fit the motions of the planets he refused to use even a
single epicycle, because to him, the centre of an epicycle was empty space, and empty space could not exert
a force on a planet. In Newton’s time the discussions about motion were often concerned with trying to find
the law of force between the Sun and the planets which would produce the planetary motion that Kepler had
described.
In 1667 Isaac Newton published the Principia. In this famous three volume work Newton set out the three
laws of motion governing all moving objects, and the law of universal gravitation would explain the motions
of the planets in terms of a mutual force of attraction between them and the Sun.
With these laws Newton explained the motions and trajectories not irony of the planets but also of all
celestial and terrestrial objects – he united both celestial and terrestrial mechanics in one set of laws. This is
referred to as Newtonian synthesis.
Newton’s deduction of the law of universal gravitation
1 Newton showed that a central inverse square force is responsible for the elliptical orbit of the planets (Kepler’s first
Law). ie. He showed that
A
Any object acted upon by an attractive central force will orbit the centre:
B.
If the central force also obeys an inverse square law with respect to distance from the centre, ie
if F  12 , then the orbit will be a conic function: circle, ellipse, parabola or hyperbola.
R
C. Depending upon the initial velocity and position of the object subject to the central inverse square force,
the orbit will be open (parabola or hyperbola) or closed (circle or ellipse):
Sun
Parabola
Sun
Hyperbola
Sun
Circle
Sun
Ellipse
23
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
2 Newton then used Kepler’s Law of periods (the third Law) to derive his Law of universal gravitation:
Derivation of the law of universal gravitation using Kepler’s third Law
Consider a planet in a circular orbit about the Sun:
2
2
ac  v , so ac  4 2 R , since v  2R
R
T
T
3
3
4 2 K s
2
R
R K

T

Now from Kepler’s Third Law:

a

s
c
Ks
R2
T2
4 2 K s m p
Fsp  m p ac 
From Newton’s Second Law:
R2
Now Ks depends upon the sun, so let 4 2 K  Gms where G is a universal constant, thus
Centripetal acceleration
Fsp  G
ms m p
R2
towards the Sun
Newton’s verification that F  12 : the link between celestial and terrestrial mechanics
R
Newton used the fact that the Earth has a moon to test whether a celestial object (the moon) obeys the same
laws as a terrestrial object (such as a falling stone) by testing whether F  12 is true for both.
R
Prediction of the centripetal acceleration of the moon in its orbit using Newton’s Law of universal
gravitation
ms me
Re2
m m
Gravitational force on the moon at its orbital distance from the Earth Fem  mm ae  G m 2 e
Re
Fes  ms ae  G
Gravitational force on a stone near the surface of the Earth
2
a
R  m
 m  e  . m
ae  Rm  ms
Rm
2
Now if our stone has the same mass as the moon
Thus acceleration of moon in its orbit
Re
2
R 
am  ae . e   9.81X  1 
 60 
 Rm 
 am  0.00272ms 2
2
Calculation of the moon’s centripetal acceleration using the formula from terrestrial mechanics ac  v to
R
check the predicted value obtained:
Moon


4 Rm 4 3.8 X 10
ac  v 

 0.00272ms 2
2
2
6
Rm
Tm
2.36 X 10
2
2
2

8

Rm
v
Earth
24
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
The agreement is exceptionally good and was the first quantitative correlation between an earthbound
phenomenon and a heavenly phenomenon. This Newton did when he was about 24 years old, at a time when
he had retired from Cambridge due to the plague. He wrote:
“… and the same year I began to think of gravity, extending to ye orb of the moon, and… from Kepler’s rule
(Kepler’s third Law)… I deduced that the forces which keep the planets in their orbits must be reciprocally
as the squares of their distances from the centres about which they revolve: and thereby compared the force
requisite to keep the moon in her orb with the force of gravity at the surface of the Earth and found them
answer pretty nearly. All of this was in the two plague years of 1665 and 1666, for in those days I was in the
prime of my age…”
Verification that force is proportional to mass and the determination of G: the Cavendish experiment
Verification that the gravitational force acting between two bodies is directly proportional to the product of
their masses was not forthcoming until a century and a half after Newton had published his law. In 1798
Henry Cavendish developed an instrument to measure the feeble force between two objects in the laboratory:
kd 2
F  GMm

k


G

Mm
d2
where k = torsional constant of the quartz fibre
Cavendish’s value
G = 6.754 X 10-11
Today’s value
G = 6.673 X 10-11
(Heyl & Chranowski, 1942)
Cavendish’s value differs
by only 1.5%!
Corollary: Weighing the Earth
For a satellite of the earth, such as the moon:
R3
4 2 k e  Gme where k e  m2
Tm
8
Rm = 3.80 X 10 m
Tm = 27.32 days = 2.36 X 106 s
4 2 ke
 me 
 5.8 X 10 24 kg
G
Today’s value me = 5.98 X 1024 kg
25
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
The Relation between G and g (at the earth’s surface)
Gravitational force: F  mg  G
me m
Gm
 g  2e
2
Re
Re
Variations in g
The value of g varies over the earth due to a number of
factors:
1. Distance from the earth
m
(a) g  G 2e if R Re
R
(b) g  Gme R if R<Re
2. The rotation of the earth on its axis
3. The non-spherical shape of the earth. The earth is
about 15 metres higher at the North pole than it is
at the South pole.
4. The non-uniform density of the earth.
Satellites and Projectiles
1. Energy of a Satellite
ET = constant = PE + KE
Gme ms 1
 ms v 2
R
2
if ET < 0 then the satellite is bound to the earth and orbits it.
If ET  0 then the satellite is free from the earth and escapes.
ie
ET  
2. Orbital Velocity
A satellite orbits the earth when ET < 0 and centripetal force Fc= gravitational force Fg
ie
ms vo2
mm
Gme
 G e 2 s  vo 
Ro
Ro
Ro
3. Minimum Escape Velocity
A satellite will just escape the earth’s gravitational influence when ET = 0. Let the satellite’s launch velocity
mm
when this occurs be ves, ie
 G e s  1 ms ves2  0
Re
2
 ves 
2Gme
Re
26
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Black-Body Radiation
In order to understand something about the colour of stars we must visit some ideas that were established last
century. Firstly one must accept that the energy delivered by a single photon (particle) of light is given by the
formula:
Energy E (Joules) = h.f (frequency Hz)
where h is Planck's Constant = 6.62618 X 10-34 Js-1.
This means that higher frequency (hence shorter wavelength) light contains more energy. For the visible
spectrum, red has the least energy and violet has the most.
Secondly, many objects, including stars, can be thought of as a black box (body) with a tiny hole in it through
which the radiation can escape. Normally such bodies will radiate out light at all frequencies but not equally.
The distribution of frequencies depends on the temperature of the box. viz.
It is common experience that the hotter an object
gets, the more blue tends to be the light that it emits.
Consider a stove element. When it is reasonably cool
it emits a dull red glow. As it gets hotter the glow
changes from red through to orange to perhaps even
yellow. Other materials can continue to go through
the spectrum of colours as they get hotter until they
start emitting all the colours (which we perceive as
white light).
It is important to note that even at low temperatures
an object can still emit high energy light but the
proportion of this light is small compared to the other
lower energy forms of light.
Hence red stars are comparatively cooler than
yellow stars which are in turn cooler than white stars
while blue stars are the hottest objects that we can
detect.
Although for the last few thousand years we have Figure 6 - Black-Body Radiation
used visible light to detect the stars, many stellar at Different Temperatures
object radiate energy from the radio wavelengths
(lowest energy) through to cosmic rays (which are above gamma rays in energy), and it is only this century that
we have been able to detect these radiations which are invisible to us. For instance, even though we cannot "see"
a black hole, as matter is dragged into it enormous amounts of energy are released in the X-ray region of light
which we can detect using X-ray telescopes (like the one which was put into orbit in 1990).
27
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Preliminary Physics C5: The Cosmic Engine Activity 2: Probable Origins of the universe
Aim: To identify data sources and gather secondary information to describe the probable origins of the
universe
Outcomes Assessed
o accessing information from a range of resources, including popular scientific journals, digital
technologies and the Internet (12.3a)
o extracting information from numerical data in graphs and tables as well as written and spoken
material in all its forms (12.3c)
o summarising and collating information from a range of resources (12.3d)
o identifying practising male and female Australian scientists, and the areas in which they are
currently working and in formation about their research (12.3e)
Write a 500 word report on this issue, including relevant diagrams.
A bibliography must be included and in-text referencing used.
Preliminary Physics C5: The Cosmic Engine Activity 3: Luminosity
Aim: To gather secondary information to relate brightness of an object to its luminosity and distance
Outcomes Assessed
o accessing information from a range of resources, including popular scientific journals, digital
technologies and the Internet (12.3a)
o extracting information from numerical data in graphs and tables as well as written and spoken
material in all its forms (12.3c)
o summarising and collating information from a range of resources (12.3d)
o identifying practising male and female Australian scientists, and the areas in which they are
currently working and in formation about their research (12.3e)
Write a 500 word report on this issue, including relevant diagrams.
A bibliography must be included and in-text referencing used.
28
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Preliminary Physics C5 The Cosmic Engine Activity 4: The Hertzsprung-Russell Diagram
Aim: 1. To gather information from secondary sources to demonstrate the star groups that emerge when
many stars are plotted on a Hertzsprung-Russell diagram
2. To process and analyse information using the Hertzsprung-Russell diagram to examine the variety
of star groups, including main sequence, red giants, and white dwarfs
3. To gather information from secondary sources to examine the Hertzsprung-Russell diagram of
open and globular clusters and use available evidence to deduce the life cycle of a star
Outcomes Assessed
o
o
o
o
o
assess the accuracy of any measurements and calculations and the relative importance of the data
and information gathered (12.4a)
identify and apply appropriate mathematical formulae and concepts (12.4b)
justify inferences and conclusions (14.1b)
identify and explain how data supports or refutes an hypothesis, a prediction or a proposed solution
to a problem (14.1c)
predict outcomes and generate plausible explanations related to the observations (14.1d)
make and justify generalisations (14.1e)
Method
Plot a HR diagram for the data given in the table below. Plot using a different coloured pen for the two sets
of data.
Table 1: Nearest Stars
Name
Proxima centauri
-centauri
Munich 15040
Lalande 21 185
Wolf 359
Sirius A
B.D. – 12° 4523
Corboda Vh. 243
Ross 248
-Ceti
Procyon
-Eridani
61 Cygni
Lacaille 9352
-2398
Groombridge 34
-Indi
Krüger 60
Van Maanen’s
Lalande 8760
O.A. (N) 17 415
* Binary Star
Magnitude
Apparent
Absolute
10.5
15.5
0.06
4.7, 6.1
9.7
13.4
7.6
10.7
13.5
16.5
-1.6
1.3
9.5
12.1
9.2
11.7
13.8
16.3
3.6
6.1
0.5
3.0
3.8
6.3
5.6
8.0
7.4
9.7
8.8
11.1
8.1
10.4
4.7
6.9
9.3
11.4
12.3
14.3
6.7
8.6
4.3
11.2
Table 2: Brightest Stars
Spectral type
M
G0, K5*
M
M2
M4
A0
M5
M0
M6
K0
F5
K0
K5
M0
M4
M2
K5
K5
F0
M0
K
Name
Sirius
Canopus
-Centauri
Vega
Capella
Arcturus
Rigel
Procyon
Achernar
-Centauri
Altair
Betelgeuse
-Crucis
Aldebaran
Pollux
Spica
Antares
Fomalhaut
Deneb
Regulus
-Crucis
Castor
Magnitude
Apparent
Absolute
-1.58
1.3
-0.86
-7.4
0.06
4.7, 6.1
0.14
0.6
0.21
-0.6
0.24
-0.2
0.34
-5.8
0.5
3.0
0.60
-0.9
0.86
-3.9
0.89
2.4
0.92
-2.9
1.05
-2.7, 2.2
1.06
-0.1
1.21
1.2
1.21
-3.1
1.22
-4.0
1.29
2.0
1.33
-5.2
1.34
0.2
1.50
-2.5
1.58
1.4, 2.2
Spectral Type
A0
F0
G0, K5
A0
G0
K0
B8
F5
B5
B1
A5
M0
B1, B1*
K5
K0
B2
M0
A3
A2
B8
B1
A0, A0*
29
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Results
1. Comment on the distribution of the two sets of data in terms of:
(a) star type
(b) variety
(c) relative magnitude
2. On your HR diagram, indicate
(a)
(b)
(c)
(d)
(e)
the main sequence
red giants and supergiants.
Blue giants and supergiants.
Variable stars.
White dwarfs
3. Gather information from the internet to obtain the Hertzsprung-Russell diagram of open and globular
clusters and use available evidence to deduce the life cycle of a star
30
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Preliminary Physics C5 The Cosmic Engine Experiment 5: Radioactivity
Part A: , ß- and -radiations
Aim: To perform a first-hand investigation to gather information to determine the penetrating power of alpha,
beta and gamma radiation on a range of materials
Outcomes Assessed
o
o
o
o
carrying out the planned procedure, recognising where and when modifications are needed and
analysing the effect of these adjustments (12.1a)
identifying and using safe work practices during investigations (12.1d)
using appropriate data collection techniques, employing appropriate technologies, including data
loggers and sensors (12.2a)
measuring, observing and recording results in accessible and recognisable forms, carrying out
repeat trials as appropriate (12.2b)
Method
Your teacher will show you the use of the Geiger counter and demonstrate the following:
(0) Background Radiation Count
(a) Penetration of the Radiations through Materials
(b) Ionising Effect of the Radiations
(c) Deflection by Magnetic Fields
(d) Deflection by Electric Fields
(e) Radiation Count and Distance Measurements
Results
Record your results in a table.
Discussion
1. Which radiation penetrates the most? The least?
2. Is there a correlation between depth of penetration and amount of deflection in E & B-fields?
3. The radiations which are deflected by E- & B-fields are said to be ionising radiations. Explain why this
term can be applied to them and which is the most ionising radiation.
4. Why is it that only these three types of radiation are detected? Why aren't other types also found?
Part B: Modelling Radioactive Decay Using Dice.
Aim: To provide a mathematical model for radioactive decay using a simulation.
Background
Radioactive decay is a random event. As such, there are a few mathematical theories which can
determine the outcome of a probabilistic event, such as throwing dice. In this simulation each die will
represent a radioactive atom which undergoes a spontaneous decay to another atom, and hence is
effectively removed from the bulk of the sample.
Method
1. Place 100 dice in a container.
2. Shake the container well and then remove and count the number of dice which come up with the number
"1".
3. Repeat step 2 until all the dice are removed.
4. Graph the number of dice left vs. roll number.
5. If you have time and have determined the half-life of the dice, check this result by putting all 100 dice
back into the container and going for 2 rolls.
31
Physics – Preliminary – Module 8.5 The Cosmic Engine – Teaching Program
Discussion
1. Is there any way to predict when a particular die/atom will "decay"? Justify your answer.
2. From your graph, determine the half-life of the dice.
3. Does your graph conform to the standard graph for radioactive decay? Why / why not?
4. What would happen to the half-life of the dice if each die had:
(a) 4 faces?
(b) 8 faces?
(c) 16 faces?
(d) 2 faces?
Can you quantify your answer (take 6 faces as 1)? You can try the last option for yourself.
5. In many samples the actual count of disintegrations is higher than can be predicted. Why?
Preliminary Physics C5 The Cosmic Engine Activity 6:
Aim: To identify data sources, gather and process information and use available evidence to assess the
effects of sunspot activity on the Earth’s power grid and satellite communications
Outcomes Assessed
o
o
o
o
o
o
o
o
accessing information from a range of resources, including popular scientific journals, digital
technologies and the Internet (12.3a)
extracting information from numerical data in graphs and tables as well as written and spoken
material in all its forms (12.3c)
summarising and collating information from a range of resources (12.3d)
identifying practising male and female Australian scientists, and the areas in which they are
currently working and in formation about their research (12.3e)
identify and apply appropriate mathematical formulae and concepts (12.4b)
evaluate the validity of first-hand and secondary information and data in relation to the area of
investigation (12.4d)
assess the reliability of first-hand and secondary information and data by considering information
from various sources (12.4e)
assess the accuracy of scientific information presented in mass media by comparison with similar
information presented in scientific journals (12.4f)
Write a 500 words report on this issue
32