Transcript Phys 104 – Honors Astronomy - Gardner

Did you get the Key
Ideas from the
Seasonal Stars Lecture
Tutorial?
Post Tutorial Question

What component of Earth’s motion causes the stars
to rise earlier on successive nights?
A) its rotation about its axis
B) its orbit around the Sun
C) the tilt of its rotation axis
North
Star
Aquarius
Pisces
Capricornus
Aries
1 day
Sagittarius
Taurus
Scorpius
365 days
Libra
Gemini
Virgo
Cancer
Leo
Figure 1
Taurus
Aries
Gemini
South
Pisces
Cancer
E
Figure 2 – What it
would look like if you
were the observer in
Figure 1
W
Two months from
the time shown
what constellation
will be high in the
Southern sky, at
Midnight?
At Noon?
What sign will a
person be if they
are born at that
time?
For more practice at this – Look back at
Part I of the “Seasonal Stars” Lecture
Tutorial
Post Tutorial Question

One night, you see the star Sirius rise at exactly 7:36
PM. The following night it will rise
A) slightly earlier.
B) at the same time.
C) slightly later.
Post Tutorial Question

One evening at midnight, you observe Leo high in
the southern sky at midnight. Virgo is to the east of
Leo and Cancer is to the west. One month earlier,
which of these constellations was high in the
southern sky at midnight?
A) Leo
B) Virgo
C) Cancer
How do we define what time it is?
What time is it now?
http://www.jgiesen.de/SiderealTimeClock/index.html
How do we define what time it is?
What time is it now?
http://www.jgiesen.de/SiderealTimeClock/index.html
How do we define a day?
Tutorial: Solar vs. Sidereal Day
p.11
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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 don’t understand what the
Lecture Tutorial is asking, ask me for help.
Which takes longer to complete?
A) one solar day.
B) one sidereal day.
C) Both take the same amount of time.
Image that Earth begins orbiting the Sun twice
as fast while maintaining the same rotation
rate. It now orbits once around the Sun every
6 months. In this case, what happens to the
length of the solar day?
A) It gets slightly longer.
B) It does not change.
C) It gets slightly shorter.
D) It is cut in half.
E) It doubles.
The changing position of the Sun during the year!
How can we describe the motion of the sun in
the sky?
meridian
east
X Zenith or overhead
south
west
How can we describe the motion of the sun in the sky?
meridian
zenith
LUNCH!!
PM or post
meridian
AM or ante
meridian
east
south
west
Where is the Sun at noon today?
zenith
here or
there?
east
south
west
Where is the Sun at noon today?
zenith
What about
tomorrow at
noon?
there
east
south
west
What about the path of the Sun?
zenith
What about
tomorrow at
noon?
there
JUST A
LITTLE
LOWER !!
east
south
west
Where is the Sun throughout the year?
Mar 21
(Vernal) and
Sept 21
(Autumnal)
Equinox
zenith
June 21
Summer
Solstice
Dec 21
Winter
Solstice
east
south
west
The time for
the sun to go
from being
highest in the
sky at noon,
to lowest and
back to
highest again
is…
east
zenith
south
ONE
YEAR
west
Where would the Sun be on your birthday?
Hour by hour of path of sun
from the southern hemisphere!
Position of the Sun when photographed during
the day of the winter and summer solstice
Shadow Paths
Sundial Time Lapse
Path of the Sun when photographed from
Phoenix, the Mars rover, up near
the north pole of Mars.
Sun at the exact same time
of the day over the course of
a full year.
The shape is called an analemma.
This picture shows every 10 days.
Altitude of the Sun Animation
•
•
•
Note where the sun rises and sets
Note how the altitude of the sun changes during a
day and over the course of the year.
Note how the shadow changes during a day and
over the course of the year.
http://astro.unl.edu/naap/motion3/animations/sunmotions.swf
Tutorial: Path of the Sun
p.87
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

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 don’t understand what the
Lecture Tutorial is asking, ask me for help.
Under which of the following circumstances will a
vertical flagpole not cast a shadow as seen from
the continental United States?
A.
B.
C.
D.
E.
0/0
every day at noon
every day at the time when the sun is highest in the sky
when the sun is highest in the sky on the summer solstice
when the sun is highest in the sky on the winter solstice
none of the above
If you are located in the continental U.S. on the first
day of October, how will the position of the Sun at
noon be different two weeks later?
A.
B.
C.
D.
E.
It will have moved toward the north.
It will have moved to a position higher in the sky.
It will stay in the same position.
It will have moved to a position closer to the horizon.
It will have moved toward the west.
For an observer in the continental U.S., which, if any,
of the x’s (a – e) in the figure below
correctly shows the position of the Sun’s shadow at
noon? Choose all that could be correct.
Note that the position of the Sun’s shadow at noon on
the Winter and Summer Solstices are
shown.
NORTH
For an observer in the
continental U.S., which of
the three shadow plots,
shown at right, correctly
depicts the Sun’s motion
for one day?
x
x
B.
C.
D.
E.
x
x
x
x
Shadow
plot B
x
x
WEST
A.
x
Shadow
plot A
x
x
x
x
x
x
x x
x
x
EAST
x
x
x
Shadow
plot C
SOUTH
Shadow plot A
Shadow plot B
Shadow plot C
More than one of the plots are possible, on different days of the
year.
None of the plots are possible.
Time?
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What causes Seasons?
Angular Momentum
•
If something is
spinning, the axis of
rotation resists a
change in direction.
Precession
26,000 years
Time?

What causes Seasons?
Hour by hour of path of sun
from the southern hemisphere!
When the Sun is high in the sky during the day, the number of
daylight hours is greater and the amount of direct sunlight
received is greater. This results in Summer.
When the Sun is high in the sky during the day, the number of
daylight hours is greater and the amount of direct sunlight
received is greater. This results in Summer.
When the Sun is low in the sky during the day, the number of
daylight hours is less and the amount of direct sunlight
received is less. This results in Winter.
When the Sun is low in the sky during the day, the number of
daylight hours is less and the amount of direct sunlight
received is less. This results in Winter.
The tilt of Earth’s axis of
rotation produces longer (or
shorter) hours of more (or less)
direct sunlight
The tilt of Earth’s axis of rotation produces longer (or
shorter) hours of more (or less) direct sunlight
Which positions (1, 2, 3, or 4) correspond with which seasons
(fall, summer, spring, winter) for the northern hemisphere?
What about the southern hemisphere?
1
4
2
3
Looking at the images below, which letter (a-e) best
represents winter in the United States?
Sunlight
Sunlight
a
c
d
2
3
b
Sun
Note: this drawing is not to scale. In fact you could fit more than 11,000 Earths between the Sun and the Earth.
e
The tilt of Earth’s axis of rotation produces
longer (or shorter) hours of more (or less)
direct sunlight
What are the possible dates for positions 1, 2,
3, and 4?
1
4
2
3
Time?
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Seasons on Mars?
Tutorial: Seasons
p.91
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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 don’t understand what the
Lecture Tutorial is asking, ask me for help.
Which of the locations identified with an “x” for each of the
situations (A – E) would experience the coolest temperature
over the course of one day?
Which of the following describes one reason that the Northern and
the Southern Hemispheres have different seasons at the same
time?
a. The Earth is closer to the Sun during summer in the Southern
Hemisphere and is farther from the Sun during winter in the Northern
Hemisphere.
b. During a day of the year when the Sun is high in the sky in the
Northern Hemisphere it will be low in the sky in the Southern
Hemisphere.
c. Earth is tilted, so the Sun is closer to one hemisphere than the other,
which causes one hemisphere to be in winter and the other in summer.
d. The energy received at Earth from the Sun changes throughout the
year providing more energy to one hemisphere than the other.
e. None of the above.
Which of the following locations experiences
the smallest amount of change in sunlight over
the course of a year?
h of the following locations experiences the smallest amount of change in sunlight
a. north pole
b. south pole
c. equator
d. They all experience the same amount of
change in sunlight over a year.
ourse of a year?
north pole
south pole
equator
They all experience the same amount of change in sunlight over a year.
If Earth were tilted more (60o rather than 23.5o), then during winter at
your location you would:
a. experience cooler temperatures.
b. experience warmer temperatures.
c. not experience any significant change in temperature.
GO CONFIDENTLY IN THE
DIRECTION OF YOUR DREAMS!!
LIVE THE LIFE YOU’VE IMAGINED