Download Night Sky II Annual Motion Seasons Planetary Motion

Night Sky II
Annual Motion
Seasons
Planetary Motion
(Take 2)
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
Quotes & Cartoon of the Day
“Astronomy is useful because
it raises us above ourselves; it
is useful because it is grand;
…. It shows us how small is
man's body, how great his
mind, since his intelligence
can embrace the whole of this
dazzling immensity, where his
body is only an obscure point,
and enjoy its silent harmony.”
— Henri Poincaré, The Value
of Science, George Halsted
translation, 1907.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Announcements
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First HW, through part of today’s material, posted
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due next Tuesday 9/22
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Last Class
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LT Position
Annual Motion
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Zodiac
Seasons
Planetary Motion (time permitting)
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
This Class
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Annual Motion
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Zodiac
Seasons
Planetary Motion
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
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
LA Mission College
Levine F2015
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.
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Like a merry-go-round that takes a year to
make one rotation
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Constellation Transiting at Midnight Changes
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Midnight — direction opposite Sun
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
“The Sun is In”
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Constellation “behind” the Sun
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
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
LA Mission College
Levine F2015
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
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Seasonal Constellations
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
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
LA Mission College
Levine F2015
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
Levine F2015
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
Levine F2015
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
LA Mission College
Levine F2015
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
LA Mission College
Levine F2015
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
LA Mission College
Levine F2015
Axial Tilt
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
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
Levine F2015
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
LA Mission College
Levine F2015
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
LA Mission College
Levine F2015
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
Levine F2015
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
LA Mission College
Levine F2015
The Length of the Day
Northern summer =
southern winter
Northern winter = southern summer
longer days mean more total exposure
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
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
LA Mission College
Levine F2015
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
LA Mission College
Levine F2015
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
Levine F2015
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?
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
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
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Planets... the Wanderers
Astronomy 1 — Elementary Astronomy
LA Mission College
Spring F2015
Planets... the wanderers
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It was a warm summer evening in ancient Greece....
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
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
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
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
Levine F2015
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
Levine F2015
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
LA Mission College
Levine F2015
WRAP-UP
Topic for Next Class
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Night Sky III
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Lunar Phases
Eclipses
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Reading Assignment
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Ch 2 in either text
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015
Homework
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Sci, Annual, Diurnal due 9/22
Astronomy 1 - Elementary Astronomy
LA Mission College
Levine F2015