Transcript Integrative Studies 410 Our Place in the Universe

Simple observations – profound
Questions
• Just using eyes & brain can provoke
“cosmological” questions:
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Is the Earth the center of the Universe?
How far away are Sun and Moon?
How big are they?
How big is the Earth?
How heavy is the Earth?
Earth or Sun the Center?
• Aristotle (384–322 BC)
– Argued that the planets move on spheres around the
Earth (“geocentric” model)
– Argues that the earth is spherical based on the shape of
its shadow on the moon during lunar eclipses
• Aristarchus (310–230 BC)
– Attempts to measure relative distance and sizes of sun
and moon
– Proposes, nearly 2000 years before Copernicus, that all
planets orbit the Sun, including the Earth
(“heliocentric” model)
Counter Argument
or not?
• Objection to
Aristarchus’s model:
parallax of stars is not
observed (back then)
• Aristarchus argued that
this means the stars must
be very far away
Measuring the Size of the Earth
• Eratosthenes (ca. 276 BC)
– Measures the radius of the earth to about 20%
Documentation discerns subtle Effects
Hipparchus (~190 BC)
– His star catalog a
standard reference
for sixteen centuries!
– Introduces
coordinates for the
celestial sphere
– Also discovers
precession of the
equinoxes
How far away is the Moon?
• The Greeks used a special configuration of
Earth, Moon and Sun (link) in a lunar eclipse
• Can measure EF in units of Moon’s diameter,
then use geometry and same angular size of
Earth and Moon to determine Earth-Moon
distance
That means we can size it up!
• We can then take distance (384,000 km)
and angular size (1/2 degree) to get the
Moon’s size
• D = 0.5/360*2π*384,000km = 3,350 km
How far away is the Sun?
• This is much harder to measure!
• The Greeks came up with a lower limit,
showing that the Sun is much further away
than the Moon
• Consequence: it is much bigger than the
Moon
• We know from eclipses: if the Sun is X times
bigger, it must be X times farther away
Simple, ingenious idea – hard
measurement
Graphs
• Making a graph
– Create a table with values of the independent
variable and the function
– Draw the coordinate system on a piece of paper
– Put in (x,y) pairs
– Connect the dots
• Example: y = 3x - 1
Daily Rising and Setting
• Due to the rotation of the
Earth around its axis
• Period of rotation:
1 siderial day= 23h56m4.1s
• 1 solar day (Noon to Noon) =24h
• Stars rotate around the
North Star – Polaris
What time is it?
• Depends on where you are on the Earth!
• Time zones ensure that the noon is really
noon, i.e. sun is at highest point
• To avoid confusion, use universal time (UT),
the time at the meridian in Greenwich
UT = EST + 5 hrs
• Daylight savings adds one hour in spring, so
UT = EDT+ 4 hrs
The Time Zones
Established to insure that sun is at highest point
approximately at noon in the middle of the time zone
Daily and yearly motion intertwined
Solar vs Siderial Day
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Earth rotates in 23h56m
also rotates around sun
 needs 4 min. to “catch
up”
Consequence: stars rise 4
minutes earlier each
night (or two hours
per month, or 12
hours in ½ year)
After 1/2 year we see a completely different sky at night!
Carl Sagan Article: Baloney
Detection Kit
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Occam's Razor
Authorities do NOT carry a lot of weight
Ask whether the hypothesis can be falsified
Use MANY hypotheses to explain
experimental facts
• There must be an independent confirmation
of the facts
• Quantify!
Bacon: The subtlety of Nature is
greater than the subtlety of
argument.
• Often Nature is much weirder than we think
(or are used to from our every day
experiences)
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At very large speeds (Relativity)
For very small objects (Quantum Mechanics)
For very dense objects (Black Holes)
Etc.
Fallacies of logic and rhetoric
• Ad hominem
• Non sequitur
• Appeal to ignorance
• Begging the question
• Observational selection
 You may influence public opinion, but for
scientific progress, all that matters is
agreement with observations