Transcript 1 month - Otterbein

Motion of the Moon
• Moon shines not by its own light but by reflected
light of Sun
 Origin of the phases of the moon
• Moon revolves around the Earth
• period of revolution = 1
month
Phases of the Moon
Phases of the
Moon (cont’d)
• Moon rotates around
earth in one month
• Moon rotates around
itself in the same time
•  always shows us the
same side!
•  “dark side of the moon”
(not dark at all!)
Eclipses
• One celestial object hidden by other or in
the shadow of another
• Solar eclipse: sun hidden by the moon
• Lunar eclipse: moon in earth’s shadow (sun
hidden from moon by earth)
• Also: eclipses of Jupiter’s moons, etc.
• Most spectacular because moon and sun
appear to be the same size from earth
Solar Eclipses
•
•
•
•
Umbra – region of total shadow
Penumbra – region of partial shadow
Totality lasts only a few minutes!
Why isn’t there a solar eclipse every month?
Solar Corona
1
Annular Eclipse
2
3
Lunar Eclipses
Moon moves into
earth’s
shadow…
…and out of it
(takes hours!)
Question
Why isn’t there
an eclipse
every month ?
Skylab Workshop
• Choose one of six possible projects
– All involve observing
•
•
•
•
May work in groups of up to four
Hand in one report per group
Due Tuesday, March 11 (strict deadline!)
Weather may be a problem, so start early!
– If you wait and the weather turns bad, you will have to
do the term paper
• Come ask me if you have questions
Writing a Report
• Introduction
• Procedure
– Describe what you did
– Give enough detail so that others could repeat your
measurements
• Presentation of data
– Tables or graphs may be helpful
– Include description, units, etc. – not just numbers
• Answers to any questions
• Conclusions
Writing a Report
• At least one paragraph per section, except for
questions
• About 2–4 pages total
• Properly cite any references (articles, books, etc.)
that you use
– See e.g. the Blair Handbook or other writing guide for
acceptable formats
• Strive for clarity – the point is to communicate!
Making Measurements
• Errors
– Random
– Systematic
• With every measurement, it is essential to provide
an estimate of the uncertainty – the likely range of
errors
• Example:
– Using a ruler marked in mm, we round to the nearest
marking – at most off by half a division, or 0.5 mm
– Cite a measurement of 15 mm as 15  0.5 mm to
indicate that the real value of the length is likely to be
anywhere between 14.5 mm and 15.5 mm
– If a theory predicts a value of 15.2 mm, then a reading
of 15  0.5 mm is in agreement with the theory but a
reading of 15  0.1 mm is probably not
#1: Now where was I?
• Determining the difference between the
solar and sidereal days
– Understand the difference before you start
• Measure interval between times when a
star returns to the same spot on the sky
• Measure times as accurately as possible
(you should be able to get to within a
second or so)
• Need 4–6 measurements, best if spread
out with a few days between each
measurement
• Ask if you have questions about the
error analysis!
To Sun
#2: Road Trip
• Measure the size of the Earth using
Shadow
Eratosthenes’s method
• Probably the most math of any of the
projects (some trig)
• Need two sets of measurements separated
(N–S) by 150 miles or so
– Detroit or Lexington, say
– Don’t go too far East or West (a little is okay)
Gnommon
#2: Road Trip (cont’d)
• Need two sets of measurements separated
(N–S) by 150 miles or so
– Detroit or Lexington, say
– Don’t go too far East or West (a little is okay)
• Ask me if you want more details on the trig, or if
you have questions about the error analysis
To Sun
• Measurements should be as close as
possible in time
Gnommon
– Ideal would be on the same day by
different group members
Shadow
#3: Where did I put that chart?
• Study variation of the rising/setting points of the
sun over time
• Need at least 10 sunrises or sunsets; more is better
• Measure time and azimuth (angle relative to
North)
– Note position of sunrise/sunset on horizon
– Measure angle to that position relative to some fixed
landmark (mountain, etc.)
#4: That thing is supposed to be a bear?
• Study the apparent motion of the
stars in the night sky
• Requires one entire (clear) night
• Most involved equipment making
of all the projects!
• Best to get out of the city; avoid
bright moon
• Every hour, measure elevations
of four stars in different
constellations using a quadrant
#5 Take a Photo!
• take long exposure photographs of the night sky.
• stars appear to rotate once around the Earth in a day
• measure the duration of one rotation, this is the
duration of a sidereal day
• Need camera capable of making long exposure photos
and tripod to mount the camera absolutely stable.
• Time required: About an hour for a couple of nights
which do not have to be adjacent.
• What to do: take photos of the night sky centered
around the north pole star, Polaris. The stars will
establish part of an arc around Polaris on the photo.
#6 Simulated Experiments
• In case weather becomes an issue
• Download manual and executable file from
webpage
• Two choices:
– Jupiter’s Moons
– Hubble Law
Development of the Scientific
Method
The Scientific Method
• Systematized by Francis
Bacon, Descartes and
Galileo in the 17th
century
• Not the only way of
knowing, but a very
successful one
• A method to yield
conclusions that are
independent of the
individual
• Conclusions are based
on observation
Francis Bacon (1561-1626)
Contemporary of Shakespeare,
Elizabeth I, Kepler and Galilei
Rejects Aristotelianism and
Scholasticism
Major Work:
• Novum Organum (1620)
(“New Tools”, the old Organum was Aristotle’s)
Francis Bacon
(1561-1626)
Novum Organum Title:
Allegory on the daring
mind: A Ship passes
through the “pillars of
Hercules”, beyond old
knowledge.
Rene Descartes – The Rationalist
Described the method to do science,
known for his mind-body dualism
Major Works:
• Discourse (1637) [full title: Discours
de la méthode pour bien conduire sa
raison et chercher la vérité dans les
sciences]
• Meditations on first Philosophy (1641)
[6 Meditations: Of the Things that we may doubt;
Of the Nature of the Human Mind; Of God: that He
exists; Of Truth and Error; Of the Essence of
Material Things; Of the Existence of Material
Things; Of the Real Distinction between the Mind
and the Body of Man]
Rene Descartes (1596-1650)
Rene Descartes’
Discourse
Describes the method to do science
in a straightforward way (see below)
Major points:
• Science must be based on
correct reasoning (logic)
• Science must be formulated in
mathematical language
Starting line:
“Good sense is the most evenly distributed thing in the world, for all people suppose
themselves so well provided with it that even those who are the most difficult to satisfy
in every other respect never seem to desire more than they have.”
A Classical Example
• Aristotle observes that during lunar eclipses the
Earth’s shadow on the moon is curved
• He assumes it will be curved for all eclipses
• A hypothesis that explains this: the earth is round
• A prediction of this theory is that the location of
the stars in the sky should be different for
observers at different latitudes
• This is confirmed by additional observations
– E.g. Canopus is visible in Egypt but not further north
Scientific Literacy
• An important skill to have in an increasingly
complex society
• As a voting citizen you should know what you
are voting on
• As a consumer you should know (or be able to
figure out) what you buy
• Makes life more interesting
• Nobody knows everything, but smart people can
figure out fast if something is obviously wrong