Outline for 05 September Tuesday

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Outline for 05 September (Tuesday)

• Review topics from Lecture 2. Finish last topic
  on the movement of Earth in its orbit special
  circles
• ( 25 minutes)
• Understanding the movement of objects in the sky
  with the help of the celestial sphere
• ( 40 minutes)
• The calendar
• ( 10 minutes)

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Eventually we want to be able to explain this
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Reminder

• Dont be alarmed if the material I cover always
  seems difficult I spend the most time on the
  most difficult concepts in the book
• Tutoring see syllabus for times
• Group Study some tips
• Office Hours after class and by appt.

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Feedback (How can I make things easier for you
with technology?)

• Post notes before lecture? O.K.
• On Monday _at_ 500 pm you will find Tuesdays
  notes, on Wednesday _at_ 500 pm you will find
  Thursdays notes.
• This will result in two sets of lecture notes
  before lecture and after (added annotation)
• What else? Ill pass around a survey on Thursday.

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Keywords

• Zenith
• Projection
• Meridian
• Tropic of Cancer
• Tropic of Capricorn
• Antarctic Circle
• Arctic Circle
• Declination
• Right ascension

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Zenith

• The direction straight up from an observer

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Landmarks on the Earths surface are marked by
the Suns position in the sky throughout the year
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Group Question What is special about each
circle?
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TipBe able to sketch this from memory
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Group Question Sketch image
(Talk your way through it)
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Individual Question

• Where on Earth would you have to be in order to
  see the Sun at the zenith?
• Equator
• Tropic of Capricorn
• Tropic of Cancer

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Individual Question

• Where on Earth would you have to be in order to
  see the Sun at zenith?
• Equator - Equinox
• Tropic of Capricorn winter solstice
• Tropic of Cancer summer solstice

It depends on the time of year.
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Individual Question

• Where on Earth would you have to be in order to
  see the Sun at zenith?
• Equator - Equinox
• Tropic of Capricorn Dec. solstice
• Tropic of Cancer June solstice

More specific
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Outline for 05 September (Tuesday)

• Review topics from Lecture 2. Finish last topic
  on the movement of Earth in its orbit special
  circles
• Understanding the movement of objects in the sky
  with the help of the celestial sphere
• The calendar

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It is convenient to imagine that the stars are
located on a celestial sphere

• The celestial sphere is an imaginary object that
  has no basis in physical reality
• However it is still a model that remains a useful
  tool of positional astronomy
• Landmarks on the celestial sphere are projections
  of those on the Earth

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• Celestial equator divides the sky into northern
  and southern hemispheres
• Celestial poles are where the Earths axis of
  rotation would intersect the celestial sphere
• Polaris is less than 1 away from the north
  celestial pole, which is why it is called the
  North Star or the Pole Star.
• Point in the sky directly overhead an observer
  anywhere on Earth is called that observers
  zenith.

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Projection

• Connect point on celestial sphere with a line to
  the center of Earth. Where line intersects
  Earth is where celestial point projects onto
  Earth.
• The North celestial pole projects on to Earths
  North pole.

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Tips for getting orientated

• First think about what you will see looking
  straight up at special points poles and equator
• Imagine you are in a dome standing on a sphere
  and you shoot a paint ball along your line of
  sight. Then the dome rotates. What happens to
  the paint mark when the dome rotates?

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Question

• Look at a star along zenith at Earths north
  pole. What happens to the star during the course
  of a day?
• Stays in the same place
• Moves south
• Moves north

20
Question

• Look at a star along zenith at Earths north
  pole. What happens to the star during the course
  of a day?
• Stays in the same place
• Moves south
• Moves north

21
Question

• Look toward horizon at Earths north pole. What
  happens to the star during the course of a day?
• Stays in the same place
• Moves vertically
• Moves horizontally

Note difference in emailed slides
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Question

• Look toward horizon at Earths north pole. What
  happens to the star during the course of a day?
• Stays in the same place
• Moves vertically
• Moves horizontally

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Question

• Look west while you are at Earths equator. What
  do you see?
• Stars moving straight up
• Stars moving straight down
• Stars moving horizontally

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Question

• Look west while you are at Earths equator. What
  do you see?
• Stars moving straight up
• Stars moving straight down
• Stars moving horizontally

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• Lets try to explain this. Observatory is in
  Hawaii.
• Which way is South?
• Which way do stars rotate?
• Why are paths half circles?
• Why no star that does not move?

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Alternative Visualizations
http//www.astronomynotes.com/nakedeye/s4.htm
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Question

• Where on Earth would you have to be for your
  zenith to pass through the celestial equator?
• North Pole
• Tropic of Cancer
• Tropic of Capricorn
• Equator

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Question

• Where on Earth would you have to be for your
  zenith to pass through the celestial equator?
• North Pole
• Tropic of Cancer
• Tropic of Capricorn
• Equator

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• Declination lines of latitude for the celestial
  sphere
• Right ascension lines of longitude for the
  celestial sphere
• Vernal Equinox defines
• (Decl, R.A.) (0,0)

Use of these will be (or were) covered in Lab
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• We usually draw pictures of how the Earth looks
  in its orbit around the Sun. Sometimes it is
  convenient to think about the path the sun takes
  on the celestial sphere throughout the year.

Suns path on the celestial sphere over the
course of a day
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Path of Sun on Celestial Sphere

• The path that the Sun (or any star) takes over a
  day is called a diurnal circle. Diurnal circles
  are parallel to the celestial equator.   On the
  day of an equinox the path of the Sun is same as
  the celestial equator.

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• The Sun appears to trace out a circular path
  called the ecliptic on the celestial sphere
  tilted at 23 ½ degrees to the equator
• The ecliptic and the celestial equator intersect
  at only two points
• Each point is called an equinox
• The point on the ecliptic farthest north of the
  celestial equator that marks the location of the
  Sun at the beginning of summer in the northern
  hemisphere is called the summer solstice
• At the beginning of the northern hemispheres
  winter the Sun is farthest south of the celestial
  equator at a point called the winter solstice

Sept 21
June 21
Dec 21
March 31
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Meridian

• Trace meridian in sky by lying on your back with
  your head pointing north. Draw a line with a
  laser pointer in the sky that connects north to
  your zenith to south.
• Local noon is defined to be when the Sun crosses
  the upper meridian, which is the half of the
  meridian above the horizon

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Outline for 05 September (Tuesday)

• Review topics from Lecture 2. Finish last topic
  on the movement of Earth in its orbit special
  circles
• Understanding the movement of objects in the sky
  with the help of the celestial sphere
• The calendar (sections 2.7, 2.8 of text)

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Positional astronomy plays an important role in
keeping track of time

• Apparent solar time is based on the apparent
  motion of the Sun across the celestial sphere,
  which varies over the course of the year
• Mean solar time is based on the motion of an
  imaginary mean sun along the celestial equator,
  which produces a uniform mean solar day of 24
  hours
• Ordinary watches and clocks measure mean solar
  time
• Sidereal time is based on the apparent motion of
  the celestial sphere

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The Moon helps to cause precession, a slow,
conical motion of Earths axis of rotation
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Precession causes the gradual change of the star
that marks the North Celestial Pole
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Astronomical observations led to the development
of the modern calendar

• The day is based on the Earths rotation
• The year is based on the Earths orbit
• The month is based on the lunar cycle
• The time for each cycle is not exactly integer
  (or constant), so astronomers use the average or
  mean day and leap years to keep the calendar and
  time consistent

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Keywords

• Zenith
• Projection
• Meridian
• Tropic of Cancer
• Tropic of Capricorn
• Antarctic Circle
• Arctic Circle
• Declination
• Right ascension

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Questions

• Textbook problems 4, 5, 6, 8, 9, 12, 17
• Textbook Box 2-1 page 27
• CD or Online Quiz for Chapter 2 5, 7, 8, 9, 11,
  12, 13, 18, 19, 20, 22, 23, 24, 29
• Dont worry about understanding Figures 2-17 and
  2-20b. Just know the reasons why the Sun is not
  a good timekeeper and the reason why no star is
  always at the North Celestial Pole.