Agenda

1
Agenda Week 7

• Lecture
• More on Motion
• Sidereal vs. Solar Motion and Models of the Solar
  System
• Lab
• Keep up Moon journal and work on Moon paper
• Norton Coordinates Lab and Movie - Privileged
  Planet

2
A more in depth explanation from last week If
Earth had no tilt, what else would happen?

• The equator would be much hotter due to the
  direct sunlight which would lead to a lower
  survival rate and little life.
• The poles would receive less direct light and
  thus be colder making the survival rate there
  lower as well.
• The species would have evolved differently
  (micro-evolution), thus different life would be
  on Earth.
• But we would have a habitable zone between the
  poles and the equator, but unfortunately it would
  be a smaller habitable region than we have now.

3
Solar Sidereal Motion andModels of the Solar
System(Week 7)
4
Why does Sidereal Motion (Time) matter?

• It is a system of timekeeping used by
  astronomers, useful because a star rises and
  sets at the same sidereal time every day, but not
  at the same solar (synodic) time which is our
  typical time system.

• Because local sidereal time is the right
  ascension (RA) of a star on the observers
  meridian, it is a direct indication of whether a
  celestial object of known right ascension is
  observable at that instant.

• Our clocks are based upon Solar time and we
  measure stars rising about 4 minutes earlier each
  day.

• Why does this happen?

The short versionbecause of Earths motion
around the Sun.

• What types of motion can be measured with the
  Sidereal system?

Sidereal Day, Sidereal Periods of Celestial
Bodies to include the Sidereal Month of the Moon
5
Sidereal Time vs. Solar (Synodic) Time

• A time-keeping system astronomers use to keep
  track of the direction to point their telescopes
  to view a given star in the night sky.
• One sidereal day corresponds to the time taken
  for the Earth to rotate once with respect to a
  distant star.

• A time keeping system based upon when the Sun is
  highest in the sky (12 pm).
• One solar day corresponds to the time taken for
  the Earth to rotate once with respect to the Sun.
  

6

• Prior to Tutorial completion, the Instructor
  will
• define parallel lines
• define period
• define high noon (in the diagram below)
• in the diagram below illustrate a 360 degree
  rotation of person/Earth with a ruler (students
  use toothpick) while Earth is still orbiting the
  Sun sketch the Earth/person in a later snapshot
• help students visualize distant stars (see
  top of page) and have
  them draw similar
  stars on their Tutorial
• f) provide every student with a toothpick

7
Solar vs. Sidereal Day - Lecture Tutorial (pg
11-12 10-20 minutes)

• STOP the Tutorial just after the Note on page
  12, put name on it and turn it in to Instructor
  next Tuesday.
• Be ready to struggle a little bit, this is a
  discovery!
• Work with a partner!
• Read the instructions and questions carefully.
• Discuss the concepts and your answers with one
  another.
• Come to a consensus answer you both agree on.
• If you get stuck or are not sure of your answer,
  ask another group.
• If you get really stuck or dont understand what
  the Lecture Tutorial is asking, ask one of us for
  help.

8
Follow up to Tutorial
Using the angle that the Earth sweeps out as it
goes once around the Sun and the number of days
in a year, the number of degrees per day that
Earth moves in orbit about the Sun is A) 365
days/180 degrees 2 days/degree B) 365 days/180
degrees 0.5 degrees/day C) 360 degrees/365 days
1 degree/day D) 360 degrees/24 hours 15
degrees/hour E) none of the above
ANSWER C or 1 degree/day for Earth revolving
about the Sun Realize that choice D or 15
degrees/hour is the rotation rate of the Earth
about its axis, which is also the rate the
celestial sphere appears to rotate.
9
Follow up to Tutorial

• During what type of a day does the Earth rotate
  through slightly more than 360 degrees?
• Synodic day which is 24 hrs
• Solar day which is less than 24 hrs
• Sidereal day which is less than 24 hrs
• Sidereal day which is more than 24 hrs
• Both A) B) above

ANSWER A One solar/synodic day corresponds to
the time taken for the Earth to rotate once with
respect to the Sun which is more than 360 degrees
and takes 24 hours.
10
Follow up to Tutorial

• During what type of a day does the Earth rotate
  through 360 degrees?
• Synodic day in 24 hrs
• Solar day in less than 24 hrs
• Sidereal day in less than 24 hrs
• Sidereal day in 24 hrs
• Both A) B) above

ANSWER C One sidereal day corresponds to the
time taken for the Earth to rotate once with
respect to a distant star.
11

• One sidereal day lasts approximately 23 hours and
  56 minutes during which time the Earth rotates
  360 degrees
• (4 minutes shorter than a solar day).
• One solar (synodic) day lasts 24 hours during
  which time the Earth rotates more than 360
  degrees.

12
Local Sidereal Time Clock
http//www.jgiesen.de/astro/astroJS/siderealClock/
Apparent Movement of a Star

• http//www.jgiesen.de/elevaz/basics/astro/stposeng
  l.htm

13
Synodic (Solar) vs. Sidereal Periodofthe Moon
( brief intro. to Moon phases)
14
In this video, be sure toa) notice how the
Earths orbit around the Sun makes the Moons
sidereal period different from its synodic
periodb) try to identify several Moon phases at
various points in the animation c) read the
blue writing, see next slide for a snapshot of
it

• http//www.youtube.com/watch?vfLhxF6cnUoQ

15
(No Transcript)
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Sidereal vs. Synodic Period of the Moon (zooming
in)
Sidereal Period is 27.32 days, Moon rotates to
the purple line (which should be parallel to the
leftmost red dotted line), 360 degrees not back
to New Moon - same phase as leftmost image
Synodic Period is 29.53 days, Moon rotates to the
orange line, more than 360 degrees back to the
same phase (new moon) as leftmost image.
17
Models of the Solar System

• Retrograde Motion of the Planets
• Geocentric vs. Heliocentric
• Keplers Laws

18
Planets were often called wandering stars because
they seem to slowly move from one constellation
to the next.
West
East
South
Mars prograde retrograde motion is in red
between May 1 and Dec. 31
19
Retrograde Motion

• Models of the universe MUST adequately describe
  this retrograde motion!

20
What did the Greeks have to say about the motion
of the Solar System?
The astronomer must try his utmost to explain
celestial motions by the simplest possible
hypothesis but if he fails to do so, he must
choose whatever other hypotheses meet the
case. -Ptolemy of Alexandria (140 A.D.)
21
Ptolemy

• He tried to create a model that would account for
  retrograde motion.
• He placed the planets in orbits (deferments)
  using epicycles.

• What is this Earth-centered theory called?

Geocentric theory (in Greek, geo means earth)
which maintained that Earth was the center of the
universe
22
For most of human history, we have thought the
universe was geocentric.
Copernicus devised the first comprehensive
heliocentric cosmogony to successfully explain
retrograde motion.
Copernicus(1473 1543 AD)
Heliocentric theory with the Sun at the center
of the universe or solar system
23
Retrograde motion is an apparent motion caused
when one planet moves from being behind another
planet to being in front of the other planet.
24
Lets watch a movie(s) of this motion.
http//www.astronomy.ohio-state.edu/pogge/Ast161
/Movies/marsretro
25
Tycho Brahe (1546-1601)
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• Tycho Brahe (1546-1601) is known for -
• First telescope observations of the sun
• First sun centered scientific model of the solar
  system or universe
• Being the worlds best naked-eye astronomer
• Creating first a theoretical model to explain
  planetary motions
• Creating first a theoretical model for explaining
  gravity

27

• Tycho Brahe (1546-1601) is known
• for -
• First telescope observations of the sun
• First sun centered scientific model of the solar
  system or universe
• Being the worlds best naked-eye astronomer
• Creating first a theoretical model to explain
  planetary motions
• Creating first a theoretical model for explaining
  gravity

28
What do we mean by Greatest Naked-eye
Astronomer? No telescope!
29
Scientists use parallax to measure distances.
30
(No Transcript)
31
Tycho Brahe measured distances using parallax
that disproved ancient ideas about the heavens

• He observed a supernova in 1572 and with this
  showed that the heavens were both changing and
  had a dimension of distance this troubled
  scholars who previously thought the heavens were
  unchanging.
• He showed that comets were objects that occurred
  in the region of the planets, not in Earths
  atmosphere.

32
Johannes Kepler1571 - 1630
He was rumored to have hated Tycho Brahe and was
in the relationship for the data. With that data
he changed the understanding of motion of
heavenly bodies forever.
33
Johannes Kepler 1571 - 1630 is Known for -

1. First telescope observations of the sun
2. First sun centered scientific model of the solar
   system or universe
3. Being the worlds best naked-eye astronomer
4. Creating the first theoretical model to explain
   planetary motions
5. Creating the first theoretical model for
   explaining gravity

34

• Johannes Kepler 1571 - 1630 is Known for -
• First telescope observations of the sun
• First sun centered scientific model of the solar
  system or universe
• Being the worlds best naked-eye astronomer
• Creating first a theoretical model to explain
  planetary motions
• Creating first a theoretical model for explaining
  gravity

35
Johannes Kepler1571 1630Keplers Three Laws
of Planetary Motion
36
Eccentricity, e

• how squashed or out of round the ellipse is
• a number ranging from 0 for a circle to 1 for a
  straight line
• e 0.02
• e 0.7
• e 0.9

37
Keplers First Law The orbit of a planet about
the Sun is an Ellipse with the Sun at one focus.
38
What is the shape of Earths orbit around the
Sun?Earth, e 0.016
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Keplers Second Law A line joining a planet and
the Sun sweeps out equal Areas in equal intervals
of time.
40
Kepler's Second Law Moviehttp//bcs.whfreeman.com
/universe6e/pages/bcs-main.asp?vcategorys00110
n01000i04110.07o0400001000ns0
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Keplers SECOND LAW

• A line drawn from the planet to the Sun sweeps
  out equal Areas in equal times
• orbital speed is not constant for an ellipse only
  for a circle
• planets move faster when near the Sun
  (perihelion)
• planets move slower when they are far from the
  Sun (aphelion)

42
SECOND LAW

• The speed a planet travels during its orbit is
  related to the distance from the star
• When the planet is near the sun the planet goes
  faster than when the planet is farther from the
  sun

Planet travels slow here
Planet travels fast here
43
Keplers THIRD LAW

• The size of the orbit (a is the length of its
  orbits semi-major axis) determines the orbital
  period, T

Thus planets that orbit near the Sun orbit with
shorter periods (T) than planets that are far
from the Sun
44
THIRD LAW

• The size of the orbit determines the orbital
  period
• planets that orbit near the Sun orbit with
  shorter periods than planets that are far from
  the Sun

45
Keplers Third Law The square of a planets
sidereal (orbital) period is proportional to the
cube of the length of its orbits semimajor axis
(T2?a3).
,T
T2
46
The Second and Third Laws

• The Third Law how the orbital periods are
  related to the orbital distances for all the
  planets in the Solar System
• planets that are in an orbit located near the Sun
  have short orbital periods
• planets that are in an orbit located far from the
  Sun have long orbital periods

• The Second Law tells us what a particular planet
  does when it orbits a Star
• The planet will move faster when it is close to
  the Sun and slower when it is farther from the Sun

47
THIRD LAW

• The size of the orbit determines the orbital
  period
• planets that orbit near the Sun orbit with
  shorter periods than planets that are far from
  the Sun

T 12 years
T 1 year
48
THIRD LAW

• The size of the orbit determines the orbital
  period
• planets that orbit near the Sun orbit with
  shorter periods than planets that are far from
  the Sun
• MASS DOES NOT MATTER

Both have T 1 year
49
According to Keplers second law, a planet with
an orbit like Earths would

1. move faster when further from the Sun.
2. move slower when closer to the Sun.
3. experience a dramatic change in orbital speed
   from month to month.
4. experience very little change in orbital speed
   over the course of the year.
5. none of the above.

50
Which of the following best describes what would
happen to a planets orbital speed if its mass
were doubled but it stayed at the same orbital
distance?

1. It would orbit half as fast.
2. It would orbit less that half as fast.
3. It would orbit twice as fast.
4. It would orbit more than twice as fast.
5. It would orbit with the same speed.

51
Keplers second law says a line joining a planet
and the Sun sweeps out equal areas in equal
amounts of time. Which of the following
statements means nearly the same thing?

1. Planets move fastest when they are moving toward
   the Sun.
2. Planets move equal distances throughout their
   orbit of the Sun.
3. Planets move slowest when they are moving away
   from the Sun.
4. Planets travel farther in a given time when they
   are closer to the Sun.
5. Planets move the same speed at all points during
   their orbit of the Sun.

52
If a small weather satellite and the large
International Space Station are orbiting Earth at
the same altitude above Earths surface, which of
the following is true?

1. The large space station has a longer orbital
   period.
2. The small weather satellite has a longer orbital
   period.
3. Each has the same orbital period

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Keplers 2nd 3rd Laws - Lecture Tutorials (pg
21-27)

• Work with a partner!
• Read the instructions and questions carefully.
• Discuss the concepts and your answers with one
  another.
• Come to a consensus answer you both agree on.
• If you get stuck or are not sure of your answer,
  ask another group.
• If you get really stuck or dont understand what
  the Lecture Tutorial is asking, ask one of us for
  help.