Homework 3 Answers

1. How was Neptune found?

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This may be easily found in your text, see pages 397-9, 413.
Accurate measurements of the motion of Uranus where used to
calculate the position of Neptune, using Newton's law of Gravity.

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2. The text book for the class sometimes presents more than
one major topic (or subject area) in a chapter. Please try to
identify the two (or more if you like) main topics in each
of the first 4 chapters.
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Variety on obvious topics available
Chapter 1: sky, gravity
Chapter 2: stars, light
Chapter 3: Solar system summary, telescopes
Chapter 4: Solar system formation, meteors

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3. We obtain evidence about the Solar System in several
very different ways. Can you list three such ways, which are as
different as possible?
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Naked eye observation, telescopic observation at all wavelengths,
analysis of light (photometry, spectroscopy), satellites in orbit about the
Earth and near to Solar system objects,
samples collected by satellites and landers,
samples which have fallen onto the Earth (meteorites, Martian rocks).

NOTE Mathematics & theories do NOT constitute evidence.
     Rather, they help us understand.

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4. We distinguish three types of activity (what scientists to
try to learn and understand more) in astronomy and physics:
theory, observation and experiment.
Please give a specific example of each.
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Theory: Big Bang, Heliocentric theory, geocentric theory, Kepler's laws
Observation: phases of moon or Venus, sunspot cycle, pictures of the stars
Experimentation: Rolling balls down inclined plane,
  analysis of the chemical composition of meteorites

NOTE: Experimentation involves a controlled environment, not just observing

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5. Given an example from astronomy where the accuracy of the
measurement was (or is) important. If the measurement had a
significantly (e.g. several times worse) accuracy, different
conclusions would have been reached.
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Accuracy helped conclude...

That planetary orbits are ellipses and not circles; Discovery of Neptune
(positional accuracy)
identification of light from different elements
(spectroscopy: each element makes light of slightly different wavelengths)

NOTE: The key is a differing conclusion. If the distance to the Sun or
moon or the period of the sunspot cycle were slightly in error,
There would be no major change in understanding.

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6. Give a concise summary of the sun. Mention all of the following:
what it is (both inside and out), what it does, how it evolves
(changes) and how it works.
a) Start my making a list of words which give an outline of your answer.
b) Then compose one or more sentences which give an accurate
summary.
c) Then edit your answer (you might want to do this on a
computer) to end up with as few words as possible.
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Info for this question is easily located in Chapter 2.
Remember, in questions like these, the key is to communicate
all the IMPORTANT information in few words. You loose points
if you miss major points and if you add unnecessary details.

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