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Tawa College.doc Printed 22:26 26/03/2015 Page 1 of 1
Tawa College Community Education, Astronomy, 10 June 2002
“The Scale of the Universe” – Class Handout, Duncan Hall [in place of Ed Budding]
Topic
Notes
Illustration
1. How could we build a scale
model of the solar system
and its relationship to our
galaxy – the Milky Way?
2. How do we measure the
size and whereabouts of
New Zealand?
1.
2.
3.
4.
5.
3. How has the size of the
Earth been estimated /
measured?
• Egypt: sunlight casting
shadow (-5% error)
• Time the sunset, run up the
hill and do it again – an
exercise for the student to
work out time difference
for 10 metre increase in
height
• The size of the Earth was
used to define the metre
• Satellite geodesy
4. How has the distance to the
Moon been estimated /
measured?
• Lunar eclipse – look at
earth’s circular shadow
(wrong by a large margin)
• Lunar parallax (~2 degrees
= 3.3 * 10-2 radians)
• Newton’s law of universal
gravitation, “G”
• Radar – in the 1920s radio
waves bounced off moon
• Laser ranging – accurate to
a few millimetres
5. How has the distance to the
Sun been estimated /
measured?
• Earth-moon-sun at
quadrature – but error prone
• Transits of Venus –
suggested by Halley in
1716; reason for Cook’s
voyages of 1761 and 1769
• Solar parallax ~9 arc
seconds = 4.3 * 10-5 radians
• Radar ranging of Venus
• A fundamental unit for
many other measures: AU
6. How has the speed of light /
radio been estimated /
measured?
• Galileo’s attempt
• Roemer’s observations of
Jupiter’s moons
• Laboratory measurements
Tawa College.doc Printed 22:26 26/03/2015 Page 2 of 1
Topic
Notes
Illustration
7. How have the distances to
the nearby / brighter stars
been estimated?
• Equivalent brightness to the
Sun: Newton in late 1600s
• Stellar parallax, accuracy
achieved in early 1800s –
base unit is AU
• Several thousand star
distances have been
estimated using parallax
from the earth’s surface
• Several tens of thousands
using satellite observatories
8. How have distances to
more distant / fainter stars
been estimated?
• Hertzsprung-Russell: both
observed a relationship
between star colour and
brightness
9. How do stars move in
space?
• First component: proper
motion
• Second component: radial
velocity
10. How are star sizes
measured?
• Michelson interferometry
• Intensity interferometry
• Lunar occultation: Fresnel
diffraction patterns
• Speckle interferometry
11. How have distances outside
our Milky Way galaxy been
estimated?
• Cepheid variable stars in
the LMC – Levitt in the
early 1900s
• Supernovae brightness
• Standard galaxy types
• Red shifts – the “Hubble
Constant”
12. Are there any other planets
out there?
• Yes!
• Strong evidence of 100+
• Eclipses
• Radial velocities
• Microlensing caused by
isolated planets in
interstellar space
13. How far out can we “see”?
What can we “see”?
Good reference sources are:
• New Scientist
• Sky and Telescope
• Scientific American
• Web sites – Google