Download A1 F2015 Seasonal.key

Night Sky II
Annual Motion
Seasons
Planetary Motion
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
Quotes & Cartoon of the Day
“You will certainly not doubt the necessity of studying astronomy and physics, if you are
desirous of comprehending the relation between the world and Providence as it is in
reality, and not according to imagination.”
— Maimonides
“Even if 'going retrograde' or 'moving into Aquarius' were real phenomena, something
that planets actually do, what influence could they possibly have on human events? A
planet is so far away that its gravitational pull on a new-born baby would be swamped
by the gravitational pull of the doctor's paunch.”
— Richard Dawkins
Astronomy 1 - Elementary Astronomy
LA Mission College
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Quotes & Cartoon of the Day
Astronomy 1 - Elementary Astronomy
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Announcements
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Last Class
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Intro to the Night Sky
Apparent Magnitude
Diurnal Motion
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LT “Position” time permitting
Astronomy 1 - Elementary Astronomy
LA Mission College
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This Class
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LT Position
Annual Motion
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Zodiac
Seasons
Planetary Motion (time permitting)
Astronomy 1 - Elementary Astronomy
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LT “Position”
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
WARM UP QUESTION FOR LT
POSITION
You observe a star rising directly in the East. When it
reaches its highest position above the horizon, where
will it be?
A. high in the northern sky
B. high in the eastern sky
C. high in the southern sky
D. high in the western sky
Astronomy 1 - Elementary Astronomy
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LECTURE-TUTORIAL “POSITION”
PP 1-2
LT Position pp 1-2
1) Is the horizon shown a real physical
horizon or an imaginary plane that extends
from your observing location on Earth out
to the stars?
2)Can the observer shown see a star when it
is located below the horizon? Why or why
not.
3)Is either Star A or Star B even in an
unobservable position? If so, which
position(s)?
4)When a star travels from a position below
the observer’s horizon to a position above
the observer’s horizon, is that star rising or
setting?
5)When a star travels from a position above
the observer’s horizon to a position below
the observer’s horizon, is that star rising or
setting?
Astronomy 1 - Elementary Astronomy
LA Mission College
Figure 1
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LT Position pp 1-2
6)Star A is just visible above your eastern
horizon at Position 1. At which of the
numbered positions is it just visible above
your western horizon?
7)At which position(s) if any, does Star B rise
and set?
8)Two students are discussing their answers
to Question 7.
Student 1: Locations B1 and B3 are on my
horizon because they are rising and setting
just like A1 and A3.
Student 2: Figure 1 shows that Star B is as
low as it will get when it is just above the
northern horizon at B4. So Star B never
goes below the horizon.
Figure 1
Do you agree or disagree with either of both
of the students? Explain your reasoning.
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LT Position pp 1-2
9)Label the directions north, south,
east and west on Figure 1.
Check your answer with another
group.
Figure 1
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LT Position pp 1-2
10)For each indicated position, describe where
in the sky you must look to see the star at that
time. Each description requires two pieces of
information: the direction you must face (north,
northeast, east, etc.) and how far above the
horizon you must look (low, high or directly
overhead). If you cannot see the star, state
that explicitly. The descriptions for four
positions are given as examples
a) A1: east, low
E
N
S
W
b) A2
c) A3
d) A4
e) North Star: north, high
f) B1
g) B2: directly overhead
Figure 1
h) B3: northwest, high
i) B4
11)Does Star B ever set?
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
You observe a star rising directly in the East. When it
reaches its highest position above the horizon, where
will it be?
A. high in the northern sky
B. high in the eastern sky
C. high in the southern sky
D. high in the western sky
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Let’s Practice
If you observe the constellation Orion just above the
horizon to the east, where will it appear to be an hour
later?
A. Closer to the horizon, to the East.
B. Further above the horizon, to the East.
C. In the same location.
D. It will not be visible.
Astronomy 1 - Elementary Astronomy
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Stars that rise due East are above the horizon 12
hours. Circumpolar stars are always above the
horizon.
About how long do you think a star that risesEnearer
the NE compass point could be aboveNthe horizon?
S
W
A. 6 hours
B. 12 hours
C. 18 hours
D. 24 hours
Astronomy 1 - Elementary Astronomy
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In the northern hemisphere, stars rise in the East, set
in the West and travel counter-clockwise in circles
around the North celestial pole.
In the southern hemisphere, the stars
A. rise in the West, set in the East and travel clockwise
around the South celestial pole.
B. rise in the East, set in the West and travel counterclockwise around the South celestial pole.
C. rise in the East, set in the West and travel clockwise
around the South celestial pole.
D. rise in the West, set in the East and travel counterclockwise around the South celestial pole
Astronomy 1 - Elementary Astronomy
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Zodiac and Apparent Solar
Motion
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
Apparent Solar Motion
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Due to Earth’s rotation, the sun & stars rise & set
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When do we see stars? What does that mean?
The Sun also appears to move against the
background stars due to the Earth’s orbit around it
Astronomy 1 - Elementary Astronomy
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Visible Night Sky Changes
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We see stars in the direction away from Sun
Which stars are visible at night changes over the orbit.
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Like a merry-go-round that takes a year to
make one rotation
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Astronomy 1 - Elementary Astronomy
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Astronomy 1 - Elementary Astronomy
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Constellation Transiting at Midnight Changes
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Midnight — direction opposite Sun
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“The Sun is In”
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Constellation “behind” the Sun
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Apparent Solar Motion
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The path the Sun appears to take is called the Ecliptic
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The Ecliptic Plane is the plane in which the Earth orbits the Sun
Planets appear near the ecliptic
The zodiacal constellations lie near the Ecliptic
Astronomy 1 - Elementary Astronomy
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Apparent Solar Motion
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Zodiac = imaginary belt about 8° on each side of the
ecliptic
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within which are the apparent paths of the sun, moon, and
principal planets.
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There are actually 13 classical constellations in the Zodiac
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Ophiucus is between Scorpius and Sagittarius
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Seasonal Constellations
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Seasonal Constellations
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Sun moves ~1
constellation per
month.
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This is ~ Dec 1
The Sun is in Scorpius
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actually Ophiucus
Taurus transits near
midnight
Astronomy 1 - Elementary Astronomy
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Seasonal Constellations
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Sun moves ~1
constellation per
month.
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This is ~ Jan 1
The Sun is in ?
? transits near midnight
Did Taurus rise earlier
or later?
Astronomy 1 - Elementary Astronomy
Cancer
Leo
LA Mission College
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Let’s Practice
If The Sun appears in Virgo in the Fall (mid Sep to late
Oct), approximately what time of year will it appear in
Sagittarius?
A. Fall
B. Spring
C. Summer
D. Winter
Astronomy 1 - Elementary Astronomy
LA Mission College
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One night, you see the
rise
at exactly
ICE 2! star Sirius
ASTRO
110/120!
Levine Spring7:36
2013
PM. The following night it will rise
Name:____________________!
!
Date:__________
A. slightly earlier.
B. at the same time.
C. slightly later.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
You go out tonight and see
the brightest
star inLevinethe
ICE 2!
ASTRO 110/120!
Spring 2013
constellation Orion just rising above your eastern
horizon at 10 PM. One week later at 10 PM this same
star will be _____.
Name:____________________!
!
Date:__________
A. slightly higher in the sky.
B. below your horizon.
C. at the same height as before.
D. setting on your western horizon.
Astronomy 1 - Elementary Astronomy
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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
Astronomy 1 - Elementary Astronomy
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SO... WHY DO WE HAVE SEASONS?
We have Seasons because we are tipped!
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The Earth’s axis is tipped 23.5° from the plane of it’s
orbit.
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Axial Tilt
Axial tilt is the cause of seasonal variations
It is NOT!!! Because the Earth’s orbit is elliptical!
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I bet you know something that tells you it can’t be this!
The Earth’s orbit is almost circular AND the point of closest
approach, perihelion, is in January
Astronomy 1 - Elementary Astronomy
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Axial Tilt
Astronomy 1 - Elementary Astronomy
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The Reasons for the Seasons
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Like a gyroscope, the Earth “holds” it’s tilt as it travels
around the Sun. The tilt does not rotate as the Earth
revolves
Astronomy 1 - Elementary Astronomy
LA Mission College
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Why does axial tilt drive the seasons?
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It’s about the transfer of Energy
Specifically energy from Sun to Earth
Astronomy 1 - Elementary Astronomy
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Energy
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Energy=capacity to start, stop, accelerate, turn, raise etc.
something
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microscopically or macroscopically
capacity to “do work” — change the energy state of something
E.g.
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kinetic energy — energy of motion
gravitational potential energy — boulder at top of hill
thermal energy — motion of atoms and molecules
chemical energy
light energy
electric potential energy — capacity to move electrons
etc.
Astronomy 1 - Elementary Astronomy
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Energy from the Sun
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Light or electromagnetic radiation
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visible light
infrared light
ultraviolet light
Net absorbtion of energy = heating
Sun puts out same energy summer & winter, but in
summer energy transfer is locally more efficient
Astronomy 1 - Elementary Astronomy
LA Mission College
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Why does the tilt affect the Solar Energy
Transfer?
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The length of the day
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Summer days are longer than winter days
The angle at which sunlight falls on the surface
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The sun appears higher in the sky in summer and lower in
winter
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Sunlight is more direct in summer
Astronomy 1 - Elementary Astronomy
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The Length of the Day
Northern summer =
southern winter
Northern winter = southern summer
longer days mean more total exposure
Astronomy 1 - Elementary Astronomy
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The Angle of Sunlight Winter vs. Summer
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Sun appears higher in the sky in summer &l ower in
winter
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lower= light hits surface at steeper angle.
Steeper angles = less concentrated light; dimmer
Astronomy 1 - Elementary Astronomy
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Terminology: Solstice & Equinox
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Tilt toward or away from Sun — solstice
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“sun stop”
start of winter or summer
Tilt parallel to Sun — equinox
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“Equal night”
start of spring or fall
Astronomy 1 - Elementary Astronomy
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Direction of Sunrise and Sunset are also affected
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At summer solstice, the Sun rises N of due E (in the
northern hemisphere)
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At winter solstice the Sun rises S of due E
This is the same reason the day length varies
Astronomy 1 - Elementary Astronomy
LA Mission College
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Let’s Practice
Which lettered position (A-E), in the image below, best
represents the location on Earth that is experiencing
winter in the Northern Hemisphere?
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If Earth were tilted more (60° rather than 23.5°), then
during winter at your location you would _____
compared to what you experience during winter now.
A. experience cooler temperatures
B. experience warmer temperatures
C. not experience any significant change in
temperature
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Planets... the Wanderers
Astronomy 1 — Elementary Astronomy
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Planets... the wanderers
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It was a warm summer evening in ancient Greece....
Astronomy 1 - Elementary Astronomy
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Apparent Motion of Planets
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Indeed originally named for their “wandering” movement
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Most of the time rise a bit later each night
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move eastward against the background stars
Sometimes appear to go “backwards” for a while
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“Late Old English planete, from Old French planete (Modern
French planète), from Late Latin planeta, from Greek
planetes, from (asteres) planetai "wandering (stars),..."
i.e. rise earlier each night/go westward
This is called retrograde motion
We will explain how this works later in the course
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Mars and Retrograde Motion
QuickTime movie from Dr. Ted Snow's web site at The University of Colorado, Boulder.)
Astronomy 1 - Elementary Astronomy
LA Mission College
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Let’s Practice
For how many days was this planet in retrograde
motion?
May
A. 10 days
B. 12 days
C. 15 days
D. 17 days
E. 32 days
Astronomy 1 - Elementary Astronomy
LA Mission College
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On which date would the planet appear to rise in the
west?
May
A. March 1
B. March 31
C. April 5
D. April 12
E. Never Ever, Never, Ever, EVER!!!!!!!
Never,
Astronomy 1 - Elementary Astronomy
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WRAP-UP
Topic for Next Class
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Night Sky III
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Lunar Phases
Eclipses
Astronomy 1 - Elementary Astronomy
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Reading Assignment
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Ch 2 in either text
Astronomy 1 - Elementary Astronomy
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Homework
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None Assigned yet
Astronomy 1 - Elementary Astronomy
LA Mission College
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