Chapter 12 – Our Place in the Universe
12.1 Observing the Universe
Learning outcomes
 astronomical distances in the Solar System can be measured by radar
 there are many units for astronomical distances including light years and parsecs
 distances to nearby stars can be found by parallax
 distances can be found using the inverse-square law for intensity of light
 some larger distances are estimated by the apparent brightness of ‘standard candles’, e.g.
Cepheid variables and Type 1a supernovae
 distant objects are observed as they once were because it has taken light time to travel
 the cosmological distance scale is still subject to uncertainty
 velocities of astronomical objects can be established by the Doppler shift with
d v


c
for v much less than c.
Lesson 1: How far away are astronomical objects and how do we know – radar and parallax
Objectives:
-
distances to nearby objects can be found using radar
distances to further objects can be found using parallax, standard
candles, Cepheid variables and inverse square law
Activity 10E: Experiment: What do you know about cosmology? And discussion
NB: the next 3 lessons can be done using the ICT sheet where students research methods of
measuring distances inside the solar system, outside the solar system but inside the galaxy,
outside the galaxy. You still need to do the expts at some point though.
Look at the powerpoint – How big is our planet
Radar:
Activity 70E: Experiment Investigating the measurement of distance using an ultrasonic sensor
Activity 80E: Experiment Tap-tap range finding
Definition of light second, minute and year as unit of distance
Looking into the night sky is like looking back in time because the light takes time to get here.
The astronomical unit (AU) (Earth sun distance) as unit of distance
Display Material 80S: Computer Screen Radar images Volcano
Display Material 100S: Computer Screen Magic from trip times
Parallax - Activity 20E: Experiment Range finding and parallax
The parsec as unit of distance
http://instruct1.cit.cornell.edu/courses/astro101/java/parallax/parallax.html
Question 50S: Short Answer Trip times tell distances or as a whiteboard quiz
Lesson 2/3:. How far away are astronomical objects and how do we know – inverse square
law, standard candles and Cepheid variables
Objectives: -
distances to further objects can be found using parallax, standard
candles, Cepheid variables and inverse square law
Inverse square law – look at butter gun in book
Activity 40E: Experiment Brightness and distance
Activity 50E: Experiment Summer Sun remembered to calculate power of Sun.
The idea of flux density in Wm-2 (like butter per slice)
To follow up: or to set for homework: choose from:
Question 40S: Short Answer Comparing intensities for lamps
Question 45S: Short Answer Jupiter and Saturn close together in the sky
Question 46S: Short Answer Brighter stars aren’t always nearer
Harder:
Question 52D: Data Handling The brighter stars in the night sky
Other methods:
Cepheid variables using the book or Question 80D: Data Handling Astronomical distances
Finish with Display Material 10O: OHT Distances in light travel time and Display Material 30O:
OHT The ladder of astronomical distances as a summary
Homework:
Piglet see above
Pooh - Question 20S: Short Answer Measuring distances within the solar system and beyond
Christopher Robin – see above
Lesson 4:. How fast are astronomical objects moving and how do we know?
Objectives:
- velocities of astronomical objects can be established by the Doppler shift
with
for v much less than c.
d v


c
Starter: How did we measure speed in Ch 8/9? Summarise methods.
Using radar:
Display Material 90O: OHT Velocities from radar ranging
Doppler shift -select from the activities below depending on time
Applet to illustrate Doppler effect.
http://www.colorado.edu/physics/2000/applets/doppler.html
http://www.lon-capa.org/~mmp/applist/doppler/d.htm
http://library.thinkquest.org/19537/java/Doppler.html
File 40L: Launchable File A Modellus model of the Doppler effect
Doppler shift song
http://www.astrocappella.com/doppler.shtml
Display Material 110O: OHT Relative velocity from radar pulses
Display Material
d v 120O: OHT The Doppler shift

You need to know

c
Using gratings to look at spectra - gas tubes. This is how we know about elements in stars (75%
hydrogen 25% helium). If we know the element we can work out the redshift.
Question 55S: Short Answer Doppler shifts in astronomy
Question 60S: Short Answer Binary stars
Laptops: Activity 90S: Software Based The space police
Activity 100S: Software Based The relativistic Doppler effect
Homework:
From above questions + this is harder
Question 30C: Comprehension Apparent star brightnesses and logarithmic scales
12.2 Was there a Big Bang?
Learning outcomes
 red shifts of distant galaxies give evidence of the expansion of the Universe. A red shift
z


corresponds to an expansion in scale of
R2
 1 z
R1
 evidence that the Universe has evolved from an initial uniform, hot dense state comes from
the existence of the cosmic microwave background.
 further evidence comes from cosmological red-shift
 Hubble’s Law is v = Hod; Galaxies further away are moving faster
 1/Ho gives an estimate of the expansion time-scale of the Universe
 current estimates of the expansion time-scale of the Universe put it at about 14 ± 2 Gy.
 there are still fundamental problems in explaining the major features of the Universe.
Lesson 5: Redshift and the big bang
Objectives:
- the difference between redshift and cosmological redshift
-
z


how this provides evidence for the expansion of the universe
how to measure expansion
further evidence is Cosmic Microwave Background Radiation (CMBR)
Difference between Doppler shift (things moving towards/away) and cosmological red-shift – the
space between galaxies is expanding. You can get Doppler blue shift but NOT cosmological blue
shift. Display Material 180O: OHT Red shifts of galactic spectra
Blow up big balloon with galaxies stuck to it
Activity with measuring the distances between galaxies when balloon partially blown up and fully
blown up to show that there is no centre.
Derivation of:
And hence
z


R2
 1 z
R1
Check out applets to show this File 70L: Executable File The space expands
Activity 130S: Software Based The cosmological red shift
Question 95S: Short Answer Redshifts of quasars
Other evidence is COBE: see ppt from 21C
Display Material 210O: OHT The cosmic microwave background radiation
Question 100S: Short Answer Cosmic microwave background radiation
Lesson 6: Hubble’s Law and the age of the Universe
Objectives:
- galaxies further away are going faster – Hubble’s Law
- the age of the universe is approx 1/H
- it is a very hard thing to measure – values have changed a lot over time.
What is Hubble's Law?
http://www.astrocappella.com/activities/how_far.html#hubbles_law
Display Material 150O: OHT The history of the Universe
Display Material 160O: OHT Hubble's law and the age of the Universe
Display Material 140O: OHT How the accepted value of the Hubble constant has changed
Great timeline:
http://resources.schoolscience.co.uk/PPARC/bang/bang.htm