http:www.phys.selu.eduallaineasc101i

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Chapter 1
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• http//www.phys.selu.edu/allain/easc101i

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What Causes the Seasons?

• 1.The tilt of the Earths axis as it orbits the
  Sun
• 2.The distance from the Earth to the Sun
• 3.The speed at which the Earth spins
• 4.The varying amount of carbon dioxide in the
  atmosphere

The tilt affects how directly the sun shines on
the Earth. The direct (90o) sunlight warms the
earth more than the angled sunlight.
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Why is it warmer in the summer?

• 1.The Sun rises higher in the sky
• 2.The tilt of the Earth makes our location closer
  to the Sun
• 3.The Earth is closer to the Sun in that part of
  the orbit
• 4.There is more carbon dioxide in the atmosphere

1 - Sun rises higher in sky.
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What causes the phases of the moon?

• 1.The phases are caused by the Earths shadow on
  the Moon
• 2.The phases are caused by clouds blocking the
  Moon
• 3.The shadow of something other than the Earth on
  the Moon
• 4.Viewing the dark side of the Moon from
  different angles

4 - Viewing the dark side of the moon from
different angles.
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What time of the day is the sun at its highest
point?

• 1.Around 1100 AM
• 2.Around 1130 AM
• 3.Around 1200 Noon
• 4.Exactly at 1200 Noon
• 5.Around 1230 PM
• 6.Around 100 PM

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Does the sun pass directlyoverhead?

• 1.Yes
• 2.No
• 3.Sometimes

Never in Hammond, sometimes at the equator.
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Video of a shadow over a day

• http//www.phys.selu.edu/allain/easc101i/page2/as
  sets/sun.mp4

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What about the motion of the stars at night?

• 1.They dont significantly move through the
  night.
• 2.They rise in the east and set in the west
• 3.They rise in the west and set in the east
• 4.They just move in circles, but dont rise or set

They rise in east set in west but also move in
circles.
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The stars over the course of a night.
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September 21
October 21
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December 21
November 21
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January 21
February 21
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April 21
March 21
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June 21
May 21
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August 21
July 21
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There are two days when the sun rises due east. 
What are they?

• Sept 21 and March 21
• Dec 21 and June 21
• Sept 21 and Dec 21
• March 21 and June 21
• Sept 21 and June 21
• Dec 21 and March 21

September March
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Which day does the sun rise in the most in the
North?

• Sept 21
• Dec 21
• March 21
• June 21
• Everyday is the same

June
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Celestial Sphere Model
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Motion of the Sun (Celestial sphere)
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If you were standing on the Earths equator,
where would you see the North celestial pole?

• 1.You could not see it
• 2.Directly North right at the horizon.
• 3.Directly above you (look straight up)
• 4.Directly East some point above the horizon
• 5.Directly West some point above the horizon.

2 - If standing on the earth's equator, the
celestial poles would appear to be right on the
horizon north / south (pg 27)
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Locating Objects
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Right Ascension

• From W to E
• Units of hours, min, sec

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Sun at summer solstice is at RA 6hours. What
is the RA of the sun atwinter solstice?

• 1 hours
• 6 hours
• 12 hours
• 18 hours
• 24 hours

sun at summer solstice is at RA 6 hours, winter
is RA 18 hours (12 hours difference b/c at
opposite sides)
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Declination

• Angle from eq.
• Measured in deg.
• From -90 to 90
• Dec of Sun at summer solstice is 23.5 degrees

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What is the declination of thesun at winter
solstice?

• -90 degree
• -23.5 degrees
• 0 degrees
• 23.5 degrees
• 90 degrees

-23.5o in winter is lowest
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When is the Sun directlyoverhead?

• Lets check the simulator

sun is never directly overhead in Hammond - is
only directly over equator on march Sept 21 -
it will be directly over Cuba on June 21 - in Dec
it lands near bottom of Brazil
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Zodiac

• zodiac breaks celestial spear into 12 (month)
• divisions are according to which constellation
  the sun is in (washing out)

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Seasons
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Phases of the Moon

• created by the moon's own shadow - the sun hits
  it at dame angle as earth but it is moving in
  relation to each
• every year gives question on final on what causes
  phases of the moon - NOT earth's shadow but is
  moon's shadow combined with relative location
• new moon - can't see any part of it b/c is on day
  side of earth
• dark side of the moon refers to the part away
  from the earth NOT the unlit part

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Sidereal vs. Synodic Period

• Sidereal - time for one revolution (27.3 days)
• Synodic - time for moon to appear in the same
  position (29.5 days)
• Moon looks bigger when closer to horizon because
  of its comparison to other objects

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Why there is not a solar eclipse every month.
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Solar vs. Lunar Eclipse

• solar is when moon is between earth sun - small
  dot hidden - happens less than once per year in
  small area of earth
• lunar is when earth is between moon sun

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How long does it take the moon to rotate once?

• 24 hours
• 27.3 days
• 29.5 days
• 1 year
• The moon does not rotate

Sidereal - time for one revolution around the
earth - 27.3 earth days
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Prehistoric Observations(people discover the
obvious.)

• Sun rises in the East and sets in the west
• Moon changes appearance
• Eclipses happen
• Planets are different than stars how?
• move at a different speed than stars
• some significantly brighter than stars
• do not twinkle like stars (created by distance)

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Many astronomical events are cyclic

• Day cycle
• sun rises sets
• Year cycle
• where the sun rises sets each day
• acient calendar systems are similar b/c set on
  sun
• Eclipses are more than a year cycle why?
• depend on location of sun moon

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Shape of the Earth

• Greeks (500 BC)
• Pythagoras - round because sphere is perfect form
• Aristotle because of shape of shadow on moon
  (eclipse)
• Also going South you see new stars (if flat would
  see same stars anywhere)

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Fig. 1.18
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Eratosthenes 240 B.C.

• Calc a circumference of  25,000 mi
• At tropic of cancer - sun is directly overhead at
  highest point on June 21
• In Alexandria the sun was not overhead at it's
  highest point - same day, same time
• Calculated same angle from center of earth
  between cities as sunlight hits in Alexandria
• Knowing the distance between Alexandria Syene
  (_at_ 500 mi) could calculate total circumference
• Ptolemy later - 18,000 mi

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Distance to moon

• Hipparchus of Nicea (150 B.C.)
• Used Earths shadow during eclipse
• Geometry to determine distance of moon in terms
  of Earths diameter
• Answer distance 30 times Earths diameter
  (about correct)

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Aristarchus

• Distance to the Sun
• Used geometric method that was valid, but
  difficult to measure (small angles)
• Answer Sun is 20 times as far as moon (wrong, it
  is 400 times as far)
• Anyway, this means the sun is very large
• Thus earth must revolve around sun
• No one listened to him - partly because it does
  not feel like earth is moving

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Which of the following statements describes the
ecliptic?

• The line of the solar and lunar eclipses on the
  celestial sphere
• The elliptical shape of the Earths orbit around
  the Sun
• The extension of the Earths path on the
  celestial sphere
• The apparent path of the Sun across the celestial
  sphere
• Both 3 and 4 are correct.

True
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Which of the following is true during the
equinoxes?

• The Sun is on the ecliptic
• The Sun is on the celestial equator
• The Sun rises due east and sets due west
• All of the above
• Only 1 and 3 are correct.

True - Always
True - Sometimes
True - Sometimes
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Which phase of the Moon do you expect to see
setting at sunset (both setting at the same time)
?

• Full Moon- it is in the same location (direction)
  as the sun
• Third quarter
• New Moon
• Waxing crescent.

True
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Development of Science

• Greeks  Deductive Reasoning is the way
• Start with the obvious and work to the specifics
• start with obvious unquestionable ideas - i.e.
  the sun rises in the east sets in the west
• then work out the consequences
• if start with a wrong conclusion, results will be
  wrong, so do not need to test
• Logic is the authority
• Good for geometry
• The way of Aristotle
• their view of reality was that there was a
  perfect idea what we see on earth was just a
  shadow of that perfect ideal
• no experiment required, just logical thought
• Monty Python witch clip is example

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Inductive Reasoning

• Galileo Galilei, Francis Bacon, Tycho Brahe
• do not start with idea but with general
  observations connect them to create idea
• Starts with the specifics (observations) and
  generalizes upwards
• Data is the authority

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Start Edit Here - 11th
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Motion of planets

• Geocentric theories - objects rotatearound the
  EarthMultiple rotating spheres (400
  BC)Retrograde motion?Good example of models
  in science

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Fig. 1.23
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Fig. 1.14
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Galileo was the first to observe the phases
of_____.

• 1.A.   The Moon2.B.   Venus

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Ptolemy (150 AD)

• Geocentric model - circles in circlesClose
  fit - but not exactToo complicated

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Fig. 1.24
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Renaissance Astronomy

• Copernicus (1500)Tried to fit data to
  Ptolemys model - failed.Heliocentric
  modelDerived distances of planets from
  sunStayed with circlesStar parallax?  Still a
  problem

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Stellar Parallax
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Tycho Brahe (1546 - 1601)

• Created better instruments formeasurementsCol
  lected good dataObserved supernova and comets
  (veryvery important - why?)Modified geocentric
  model

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Johannes Kepler (1571-1630)

• Used Tychos dataMars orbit is an
  ellipseKeplers 3 lawsPlanets move in
  ellipitical orbitsOrbital speed varies - equal
  area in equaltimesP2 a3

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Show planet applet
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Galileo (1564-1642)

• Used telescopeMoon has features - not
  perfectSun has spotsJupiter has moonsVenus
  has phases

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Isaac Newton   (1642-1727)

• Major advances in math, physics,
  andastronomyLaws of MotionCalculusUnivers
  al gravity

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During which phase of the Moon do youexpect to
observe a lunar eclipse?

• 1.A.  Full Moon2.B.   New Moon3.C.   First
  quarter4.D.  Third quarter5.E.   Lunar eclipses
  can occur at any phaseof the Moon.

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Which of the following observations did the
ancient Greeksuse to reject the suggestion that
the Earth revolves around theSun?

• 1.A.   The shadow cast by the Earth on the Moon
  during alunar eclipse is always circular.2.B.  
  The sphere is a perfect shape3.C.   The relative
  positions of the stars on the celestialsphere
  did not change during the year4.D.   They
  believed that the Earth was flat.5.E.   The
  irregular motion of the planets.

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Slides on the net not in class PPT
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History of Astronomy

• Prehistoric Before 500 BC
• Classical 500 BC to 1400AD
• Renaissance 1400 to 1650
• Modern after 1650

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Describe the daily motion of the sun

• Why is this difficult to do?
• When is the sun directly overhead?

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Tool 1 Scientific Notation

• The Earths equatorial radius is about 6,400,00
  meters
• To really understand scientific notation we first
  need to look at exponents

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Exponents

• a2
• a2 a x a
• a3 a x a x a

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a-2

• -a x -a
• (1/a) x (1/a)
• a a
• 1/(a x a)

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24 ?

• 2
• 8
• 24
• 16
• 6

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2-3 ?

• 1/8
• -1
• -6
• -8
• 1/6

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Multiplying numbers with exponents

• a2 x a3
• a2 x a3 (a x a) x (a x a x a) a5
• a2 x a3 a(23) a5
• If a 2 then
• 22 x 23 25 32
• Or .. 4 x 8 32

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Division with exponents
a5 a3

• a (5-3) . a2
• (a x a x a x a x a) / (a x a x a)

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