Scientific approach to the study of nature

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• Scientific approach to the study of nature
• Copernicus and Galileo introduced observation and
  experimentation in the 16th century.
• Science is not a set of facts.
• It is a way of conducting a dialogue about our
  physical surroundings.
• The scientific method consists of careful
  observation of nature and an open-minded creative
  search for general ideas that agree with and
  predict those observations.
• To be scientific, a statement must be capable of
  being proven wrong.

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• Scientific approach to the study of nature.
• Observation and experimentation set science apart
  from other ways of knowing - ways that are not
  less important - just different
• Philosophy Reason Logic
• Art Appreciation of form Beauty
• Pseudoscience statements
• Hypothesis that cannot be tested with
  reproducible results
• Cold fusion, ufo's, astrology. . .

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• Scientific approach to the study of nature.
• Scientific Law
• Statement of observed regularity in nature -
  attempts to describe the observations
• has a well documented history of successful
  replication and extension to new conditions
• Scientific Theory
• Statement of observed regularity in nature -
  attempts to explain the observations
• General principle offered to explain a set of
  phenomena or observed facts.
• Not all scientific predictions can be tested
  directly
• Core of earth
• Sunenergy
• Expansion of the universe
• Require modelscreative thought
• No ultimate truthsall Provisional
• Ok as long as they are not contradicted

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• Scientific approach to the study of nature.
• Model
• Simplified version of reality used to describe
  aspects of nature.
• Not synonymous with reality.
• Based on assumptions that may simplify some
  aspects of nature, or may be incomplete
  statements about nature
• Useful to make predictions that can be verified
  by experimentation or observation.

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The Scientific Method
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Hallmarks of Science

• Modern science seeks explanations for observed
  phenomena that rely solely on natural causes.
• Science progresses through the creation and
  testing of models of nature that explain the
  observations as simply as possible.
• A scientific model must make testable
  predictions about natural phenomena that would
  force us to revise or abandon the model if the
  predictions do not agree with observations.

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Occams Razor
The idea that scientists should prefer the
simpler of two models that agree equally well
with observations - the second hallmark - after
medieval scholar William of Occam (1285 - 1349).
For instance, original model of Copernicus
(Sun-centered) did not match the data noticeably
better than Ptolemy's model (Earth-centered).
Thus, a purely data-driven judgment based on the
third hallmark might have led scientists to
immediately reject the Sun-centered idea.
Instead, many scientists found elements of the
Copernican model appealing, such as the
simplicity of its explanation for apparent
retrograde motion. Was kept alive until Kepler
found a way to make it work.
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The most exciting words in science are not
Eureka (I found it) but Now thats funny.
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MOTIONS OF EARTH

• 1. ROTATION ON ITS AXIS - Day
• 2. REVOLUTION ABOUT SUN - Year
• 3. PRECESSION - Wobble of spin axis

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Motions of Earth
Motion Typical Speed
rotation 1,000 km/hr or more around axis, with one rotation taking 1 day
orbit of Sun 100,000 km/hr around Sun, with one orbit taking 1 year
motion within local solar neighborhood 70,000 km/hr relative to nearby stars
rotation of the Milky Way Galaxy 800,000 km/hr around galactic center, with one galactic rotation taking about 230 million years
motion within Local Group 300,000 km/hr toward Andromeda Galaxy
universal expansion more distant galaxies moving away faster, with the most distant moving at speeds close to the speed of light
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Rotation
The Earth rotates about its axis axis once per
day - one rotation equals one day. The axis goes
through the north and south poles and through the
center of the Earth. It rotates counterclockwise
when looking down on the north pole which means
that the sun rises in the east and sets in the
west.
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The Rotation of the Earth From Space
Earth Rotation Movie
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Earths rotation causes the stars - the celestial
sphere - to appear to rotate around the Earth.
Viewed from outside, the stars (and the Sun,
Moon, and planets) therefore appear to make
simple daily circles around us. The red circles
represent the apparent daily paths of a few
selected stars.
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The Celestial Sphere

• Envisioned by the ancients, the celestial sphere
  had Earth at the center with the stars emblazoned
  on the sphere. They thought the stars rose and
  set because the celestial sphere (the sky)
  rotated, carrying the stars from east to west.
  All stars appear to move around two points on the
  celestial sphere, the north and south celestial
  polesprojections of earths axis of rotation.
  Earth's equator projected on the celestial sphere
  becomes the celestial equator.

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Our lack of depth perception when we look into
space creates the illusion that the Earth is
surrounded by a celestial sphere. Thus, stars
that appear very close to one another in our sky
may actually lie at very different distances from
Earth.
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Constellations
Constellations - groupings of stars named after
mythical heroes, gods, and mystical beasts -
made up over at least the last 6000 years - maybe
more - used to identify seasons - farmers
know that for most crops, you plant in the spring
and harvest in the fall. - in some
regions, not much differentiation between the
seasons. - different constellations visible
at different times of the year - can use them
to tell what month it is. For example, Scorpius
is only visible in the northern hemisphere's
evening sky in the summer. - many of the
myths associated with the constellations thought
to have been invented to help the farmers
remember them - made up stories about them
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Picture at right shows a start chart of the
region around the constellation Orion. Picture at
the left is an ornate star chart printed in 1835
- shows the great hunter Orion. He is holding a
lion's head instead of his traditional bow or
shield. He is stalking Taurus, the Bull in the
upper right hand corner. Behind him, his faithful
dog, Canis Major, is chasing Lepus, the Hare.
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Constellations Western culture constellations
originated in Mesopotamia over 5000 years ago -
added to by Babylonian, Egyptian, and Greek
astronomers - current list based charts of Roman
astronomer, Claudius Ptolemy (140 AD)
In modern world - constellations redefined so now
every star in the sky is in exactly one
constellation. In 1929, the International
Astronomical Union (IAU) adopted official
constellation boundaries that defined the 88
official constellations that exist today.
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Star Names
Brightest stars named thousands of years ago -
most come from ancient Arabic Astronomers now
use Bayer designations for the brighter stars -
introduced by Johann Bayer in his star atlas
Uranometria in 1603 - consists of a Greek letter
followed by the genitive (in Latin) of the name
of the constellation in which the star
lies Aries ? Arietis Taurus ? Tauri Gemini ?
Geminorum Virgo ? Virginis Libra ? Librae
Pisces ? Piscium Lepus ? Leporis.

• brightest star of the constellation given the
  designation Alpha, the next brightest Beta, and
  so on.
• Flamsteed designations (introduced by John
  Flamsteed in 1712) - used when no Bayer
  designation exists - use numbers instead of Greek
  letters. Numbers were originally assigned in
  order of increasing right ascension within each
  constellation - due to the effects of precession
  they are now slightly out of order in some
  places.

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• A model of the celestial sphere shows the
  patterns of the stars, the borders of the 88
  official constellations, the ecliptic, and the
  celestial equator and poles.

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Latitude and Longitude
Latitude - lines of latitude parallel to Earths
equator - labeled north or south relative to
equator - from 90º N to 90º S Longitude - lines
of longitude extend from North Pole to South Pole
- by international treaty, longitude 0 (the prime
meridian) runs through Greenwich, England
Dallas latitude 32.78º N longitude 96.78º W
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• A circumpolar constellation never rises or sets -
  they are always visible.
• Your latitude determines the portion of the
  celestial sphere visible in your sky.
• (a) A Northern Hemisphere sky.
• (b) A Southern Hemisphere sky.
• At what latitude would you see the entire sky?

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Star Trails
The Southern Hemisphere
The Northern Hemisphere
The Earth's rotation causes stars to trace daily
circles around the sky. The north celestial pole
lies at the center of the circles. Over the
course of a full day, circumpolar stars trace
complete circles, and stars that rise in the east
and set in the west trace partial circles. Here,
the time exposure lasted about 6 hours - we see
only about one-quarter of each portion of the
full daily path.
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Finding the Celestial Poles
You can always find north using the North Star.
Polaris can be found using the big dipper. Draw
a line through the two pointer stars at the end
of the big dipper and follow it upwards from the
dipper about four outstretched hands width. The
big dipper is circumpolar in the US so is always
above the horizon. The south celestial pole can
be found using the Southern Cross. There is no
South Star
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The Big and Little Dippers
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Motion of the Night Sky Animation
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The height in degrees of the north star above the
horizon is the same as your latitude.
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The angle ? between the horizon and Polaris is
the latitude of the observer. If Dallas is at 33º
latitude, where is Polaris in the sky? Where is
it at the Equator?
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Angular Size
Distances in the sky measured by angular
distance Minute of arc 1/60th of a
degree Second of arc 1/3600th of a
degree Angular diameter - angular distance from
one side of an object to the other
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Revolution
Earth travels around the sun (orbits) once per
year in the same direction it rotates. Its orbit
is not quite a perfect circle - it is elliptical.
The location in the orbit of the minimum and
maximum distances from the Sun are called
perihelion and aphelion. The plane of the orbit
is called the ecliptic.
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Earths Axial Tilt
Ecliptic Plane
The Earths axis is currently tilted 23.5º to the
ecliptic. It varies over time between 22º and 25º
due the the gravitational forces from Jupiter and
the other planets.
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The axis remains at the same tilt angle - pointed
at Polaris - throughout the orbit because of
conservation of angular momentum. The ecliptic
plane is the plane of the Earths orbit. Looking
from the Earth, it is the apparent path of the
Sun (and planets) in the sky.
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The Relationship of the Celestial Equator and the
Ecliptic Plane
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The Zodiac
The Sun appears to move steadily eastward along
the ecliptic, through the constellations of the
zodiac. As Earth orbits the Sun, we see the Sun
against the background of different zodiac
constellations at different times of year. For
example, on August 21 the Sun appears to be in
the constellation Leo. Defines astral calendar.
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Suns Path Through the Zodiac
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Celestial Sphere The apparent Sphere of the sky
Celestial Poles The points about which the celestial sphere appears to rotate
Celestial Equator Projection of the Earths equator on the celestial sphere
Ecliptic Apparent annual path of the sun on the celestial sphere