Outline for 31 August Thursday

1
Outline for 31 August (Thursday)

• Review topics from Lecture 1
• ( 20 minutes)
• Ancient astronomy
• ( 10 minutes)
• Understanding the movement of Earth in its orbit
• ( 45 minutes)

2
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
• Group Study
• Office Hours

3
Feedback (How can I make things easier for you
using technology?)

• Post notes before lecture?
• On Sunday you will find Tuesday and Thursday
  notes for that week.
• What else?
• Email list?
• Other technology?

4
Outline for 31 August (Thursday)

• Review topics from Lecture 1
• ( 20 minutes)
• Ancient astronomy
• ( 10 minutes)
• Understanding the movement of Earth in its orbit
• ( 45 minutes)

5
Keywords

• Diurnal
• Sidereal
• Local Time
• Universal Time
• Ecliptic

6
Eventually we want to be able to explain this
7
Naked-eye astronomy had an important placein
ancient civilizations

• Positional astronomy
• the study of the positions of objects in the sky
  and how these positions change
• Naked-eye astronomy
• the sort that requires no equipment but human
  vision
• Extends far back in time
• British Isles Stonehenge
• Native American Medicine Wheel
• Aztec, Mayan and Incan temples
• Egyptian pyramids

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9
Eighty-eight constellations cover the entire sky

• Ancient peoples looked at the stars and imagined
  groupings made pictures in the sky
• We still refer to many of these groupings
• Astronomers call them constellations (from the
  Latin for group of stars)

10
Modern Constellations

• On modern star charts, the entire sky is divided
  into 88 regions
• Each is a constellation
• Most stars in a constellation are nowhere near
  one another
• They only appear to be close together because
  they are in nearly the same direction as seen
  from Earth

11
Outline for 31 August (Thursday)

• Review topics from Lecture 1
• ( 20 minutes)
• Ancient astronomy
• ( 10 minutes)
• Understanding the movement of Earth in its orbit
• ( 45 minutes)

12
Question

• Rotate B around A without slippage (like a gear).
  How many times does B rotate?
• 1 time
• 2 times
• 3.14 times
• 6.28 times

A
(A is glued to the table)
B
13
Question

• Rotate B around A without slippage (like a gear).
  How many times does B rotate?
• 1 time
• 2 times
• 3.14 times
• 6.28 times

A
(A is glued to the table)
B
14
Question

• Rotate B around A without slippage (like a gear).
  How many times does B rotate?
• Same as when B was a quarter
• More than when B was a quarter
• Less than when B was a quarter

A
B
(A is glued to the table)
15
Question

• Rotate B around A without slippage (like a gear).
  How many times does B rotate?
• Same as when B was a quarter
• More than when B was a quarter
• Less than when B was a quarter

A
B
(A is glued to the table)
16
Therefore

• Break the rotation of B into two parts rotation
  about the fixed quarter and rotation about
  itself. If B does not rotate about itself, it
  still rotates around the fixed quarter.

17
Earths Motion in Orbit

• Diurnal (Daily)
• Annual (Yearly)

18
The appearance of the sky changes during the
course of the night and from one night to the next

• Stars appear to rise in the east, slowly rotate
  about the earth and set in the west.
• This diurnal or daily motion of the stars is
  actually caused by the 24-hour rotation of the
  earth.

19
Sidereal Time Prep

• What happens to lines as star moves to the right?

20
Sidereal Time Prep

• What happens to lines as star moves to the right?
  Lines become more nearly parallel.

21
Sidereal Time Prep

• What happens to lines as star a small amount up
  and down when star is very, very far away? Lines
  still look parallel.

22
Sidereal Time Definition

• From text A sidereal day is the time between
  two successive upper meridian passages of the
  vernal equinox. By contrast, an apparent solar
  day is the time between two successive upper
  meridian crossings of the Sun.

23

• Sidereal Time star time
• Solar Time sun time

At 1, line points at sun and distant star
Line 1 goes through sun and distant star
24
At 2, 24 sidereal hours since 1, line is now
pointing at distant star only

• Sidereal Time star time
• Solar Time sun time

Line 1 goes through sun and distant star
At 1, line points at sun and distant star
Line 1 goes through sun and distant star
25
At 2, 24 sidereal hours since 1, line is now
pointing at distant star only

• Sidereal Time star time
• Solar Time sun time
• Which is longer?
• Sidereal day
• Solar day

At 1, line points at sun and distant star
At 3, 24 solar hours since 1, line points at sun
only
26
At 2, 24 sidereal hours since 1, line is now
pointing at distant star only

• Sidereal Time star time
• Solar Time sun time
• Which is longer?
• Sidereal day
• Solar day by 4 min.

At 1, line points at sun and distant star
At 3, 24 solar hours since 1, line points at sun
only
27
See also Box 2-2, page 35.
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Where is Cygnus 24 solar hours later?

• West
• East
• Vertical

30
Where is Cygnus 24 solar hours later?

• West
• East
• Vertical

(It will soon be over the Pacific Ocean)
31
Local Time vs. Universal Time
32
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33
Earths Motion in Orbit

• Diurnal (Daily)
• Annual (Yearly)

34
Annual Motion

• Stars appear to slowly shift in position
  throughout the year
• This is due to the orbit of the earth (in the
  ecliptic plane) around the sun
• If you follow a particular star on successive
  evenings, you will find that it rises
  approximately 4 minutes earlier each night, or 2
  hours earlier each month

35
The Seasons
36
What causes the seasons?

• Distance of the sun from earth
• Tilt of Earth with respect to the ecliptic plane

37
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38
What causes the seasons?

• Distance of the sun from earth
• Tilt of Earth with respect to the ecliptic

39
What causes the seasons?

• Distance of the sun from earth
• Tilt of Earth with respect to the ecliptic

40
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41
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42
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43
Remember

• Rotation axis always points in same direction
  with respect to far away stars
• Looking down on north pole, Earth rotates CCW
  about its axis and CCW about sun

44
The seasons are caused by the tilt of Earths
axis of rotation with respect to ecliptic

• The Earths axis of rotation is not perpendicular
  to the plane of the Earths orbit
• It is tilted about 23½ away from the
  perpendicular
• The Earth maintains this tilt as it orbits the
  Sun, with the Earths north pole pointing toward
  the north celestial pole

45
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46
Seasons

• During part of the year the northern hemisphere
  of the Earth is tilted toward the Sun
• As the Earth spins on its axis, a point in the
  northern hemisphere spends more than 12 hours in
  the sunlight
• The days there are long and the nights are short,
  and it is summer in the northern hemisphere and
  winter in the southern hemisphere
• The summer is hot not only because of the
  extended daylight hours but also because the Sun
  is high in the northern hemispheres sky
• As a result, sunlight strikes the ground at a
  nearly perpendicular angle that heats the ground
  efficiently
• This situation reverses six months later

47
Questions

• Textbook problems 10, 11, 20, 36, 47
• CD Quiz (also at http//bcs.whfreeman.com/universe
  7e) for Chapter 2 3, 4, 9, 14, 15, 23, 24

48
From Chapter 2 quiz

• The constellation Cygnus appears overhead to an
  observer in the state of New York, USA, at
  midnight on a particular night. In which part of
  the sky will this constellation appear to an
  observer at the same latitude in Montana, 30º
  farther west in longitude, if observed at
  precisely the same absolute time (Universal
  Coordinated Time, or UTC) (which will be 10 PM,
  Montana local time)?
• In the western sky.
• Overhead, of course.
• In the eastern sky.

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50
From Chapter 2 quiz

• The constellation Cygnus appears overhead to an
  observer in the state of New York, USA, at
  midnight on a particular night. In which part of
  the sky will this constellation appear to an
  observer at the same latitude in Montana, 30º
  farther west in longitude, if observed at
  precisely the same absolute time (Universal
  Coordinated Time, or UTC) (which will be 10 PM,
  Montana local time)?
• In the western sky.
• Overhead, of course.
• In the eastern sky.

51
Book Question 20

• Why is it convenient to divide the Earth into
  time zones?

52
Group Question

• Paris Hilton wants to celebrate New Years Eve
  more than three times in a 24 hour period. She
  is in D.C. Which way does her assistant tell the
  pilot to fly? Is it possible?
• East
• West
• North
• South
• Up

53

• Paris Hilton wants to celebrate New Years Eve
  many times. She is in D.C. Which way does her
  assistant tell the pilot to fly? Does she make
  it?
• East
• West
• North
• South
• Up

(She really did this)
54
Group Question

• Now she wants to tan extra long in her jet with a
  sun roof. She starts in D.C. Which way does her
  assistant tell the pilot to fly?
• East
• West
• North
• South
• Up

55
Group Question

• Now she wants to tan continuously. She starts in
  D.C. Which way does her assistant tell the pilot
  to fly?
• East
• West
• North
• South
• Up

56
Group Question (See also Chapter 2, question 36)

• Where does the term Southern Exposure come
  from?

57
Group Question

• Where does the term Southern Exposure come
  from? To help heat house in winter, have windows
  on the south side of the house.

Images from http//home.howstuffworks.com/question
174.htm