Planetary Motion Notes

EFFECTS OF
PLANETARY MOTION
Seasons, Moon Phases, Eclipses, and Tides
HISTORY
• The Ptolemaic Solar System: Planets, Sun and
Moon orbit the Earth in 'perfect' circles.
• Copernicus: Sun at the center of the solar system.
• Tycho Brahe: Observed planetary positions.
• Johannes Kepler: Planets move in elliptical orbits,
NOT circular ones.
• Galileo Galilei: Observations using his telescope
supported Copernicus and Kepler.
• Isaac Newton: Law of Universal Gravitation
explains WHY planets move in accordance with
Kepler's Laws
EFFECTS OF PLANETARY
MOTION
• Once these discoveries were made, there were
relationships made to other natural phenomena
like…
• Seasons
• Moon Phases
• Eclipses
• Tides
How does planetary
motion effect our ……
SEASONS
• What causes our seasons?
• Is it caused by the varying distance of the earth to the sun
as it travels in its elliptical path?
• NO!
• The Earth has an elliptical orbit around our Sun.
– The Earth is actually at its closest distance to the Sun in
January (called the Perihelion)
• OUR WINTER
– The Earth is its furthest distance in July (the Aphelion).
• OUR SUMMER
• Obviously, this distance change is not great enough to
change the climate.
• The Earth's 23.5 degree tilt (known as obliquity) is
important in our seasonal change.
• Obliquity is the angle between the perpendicular to the
plane of a planet's orbit and is what gives Earth its
seasons.
SEASONS
SEPTEMBER
DECEMBER
JUNE
MARCH
How does planetary
motion effect our ……
What is a moon phase?
• The Moon is a cold, rocky body about 2,160 miles
(3,476 km) in diameter, and ~ 239,000 miles (384,400 km)
from Earth.
• The Moon orbits Earth about once every 29 and 1/2 days.
• As the moon circles the Earth, the shape of the moon
appears to change.
• It has no light of its own but shines by reflecting sunlight
from its surface.
• As it circles our planet, the changing position of the Moon
with respect to the Sun gives it a series of phases.
CRESCENT
MOON
• With a crescent moon,
only a small sliver,
about one quarter of
the visible surface of
the moon is illuminated
by the sun
• With a half moon,
approximately one half of
the visible surface of the
moon is illuminated by the
sun.
– It looks like half a circle.
• A half moon is sometimes
called a quarter moon.
– this Moon has completed
one quarter of an orbit
around the Earth from
either the full or new
position and one quarter
of the moon's surface is
visible from Earth.
HALF
MOON
• With a gibbous moon,
approximately three
quarters of the visible
surface of the moon is
illuminated by the sun.
GIBBOUS
MOON
• With a full moon, the whole
surface of the moon is
illuminated by the sun
• It appears as a full circle.
• When the Moon is full, it rises at
sunset and is visible all night
long.
• At the end of the night, the Full
Moon sets just as the Sun rises.
None of the Moon's other phases
have this unique characteristic.
• It happens because the Moon is
directly opposite the Sun in the
sky when the Moon is Full.
• Full Moon also has special
significance with regard to
eclipses
FULL
MOON
NEW
MOON
• The new moon is the phase of the moon when the
moon is not visible from Earth
• This is because the side of the moon that is facing
us is not being lit by the sun
• The illuminated side of the Moon is pointed away
from Earth
• Did you ever say- “it
happens once in a blue
moon”
• When two full moons
occur in a single
month, the second full
moon is called a "Blue
Moon."
• The moon is not
necessarily the color
blue.
BLUE
MOON
Half Moon-Last Quarter
Waning Gibbous
Waning Crescent
Day 22
Day 18
Day 26
Day 29
Day 0
NEW
MOON
Day 14
Full Moon
Day 10
Day 4
Day 7
Waxing Gibbous
Waxing Crescent
Half Moon-First Quarter
How does planetary
motion effect our ……
WHAT IS A LUNAR ECLIPSE?
• A lunar eclipse is when the earth is between the sun and
the moon and it blocks the light from the sun from hitting
the moon.
It can only occur at Full Moon, and only if the Moon passes
through some portion of the Earth's shadow.
WHAT IS A SOLAR ECLIPSE?
• A solar eclipse is when the moon is between the sun and
the earth and it blocks the light from the sun from hitting
the earth.
It also can only occur at New Moon when the Moon passes
between Earth and Sun.
ONE OF EACH A MONTH?
• If Lunar Eclipses occur at full moon, and solar eclipses
occur at new moon, do we have one of each every month?
• Actually no, but why?
• The Moon's orbit around Earth is tipped about
5 degrees to Earth's orbit around the Sun.
– This means that the Moon spends most of the time
either above or below the direct line of Earth's orbit.
– Therefore, our natural satellite usually passes above or
below, it shadows and misses them entirely.
No eclipse takes place.
So How Often?
• SOLAR ECLIPSE
– At least twice a year, the geometry lines up just
right so that some part of the Moon's shadow
falls on Earth's surface and an eclipse of the
Sun is seen from that region
• LUNAR ECLIPSE
– Usually two to four times each year, the Moon
passes through some portion of the Earth's
shadows giving us a lunar eclipse
IT’S ALL ABOUT THE
SHADOWS
• The extent of an eclipse depends on the shadows being cast
• Shadows generally have two cone-shaped components, one
nested inside the other.
– Penumbra - Faint outer shadow- a zone where the suns
rays are partially blocked
– Umbra- Dark inner shadow where the shadows
overlap- a zone where the suns rays are totally blocked
PENUMBRA
UMBRA
PENUMBRA
• Only a small zone ends up in the totally blocked UMBRA
region
TYPES OF LUNAR ECLIPSES
• Lunar Eclipses have three types:
1. Penumbral Lunar Eclipse - the Moon passes
through Earth's penumbral shadow.
2. Partial Lunar Eclipse - a portion of the Moon
passes through Earth's umbral shadow.
3. Total Lunar Eclipse - the entire Moon passes
through Earth's umbral shadow.
These eclipses are usually the most
magnificent to see
TOTAL LUNAR ECLIPSE
TYPES OF SOLAR ECLIPSES
• There are only 2 types of solar eclipses
– A total eclipse
– A partial Eclipse (Annular Eclipse)
• A Total eclipse of the Sun is seen when the Moon's dark
umbral shadow sweeps across Earth's surface.
– The track of the Moon's umbral shadow across Earth's
surface is called the Path of Totality.
– It is typically 10,000 miles long but only 100 miles wide.
– In order to see the Sun totally eclipsed by the Moon,
you must be in the path of totality.
“TOTALLY” AWESOME
• The total phase of a solar eclipse is very brief.
It rarely lasts more than several minutes.
• Nevertheless, it is considered to be one of the most
awe inspiring spectacles in all of nature.
• The sky takes on an eerie twilight as the Sun's
bright face is replaced by the black disk of the
Moon.
• Surrounding the Moon is a beautiful gossemer
halo. This is the Sun's spectacular solar corona,
a super heated plasma two million degrees in
temperature.
• The corona can only be seen during the few brief
minutes of totality.
• To witness such an event is a singularly
memorable experience which cannot be conveyed
adequately through words or photographs.
TOTAL SOLAR ECLIPSE
Partial or Annular Eclipse
• The moon travels in an elliptical path
– As the Moon orbits our planet, it's distance varies.
– This variation in the Moon's distance makes the Moon's
apparent size in our sky vary.
• When the Moon is on the near side of its orbit, the Moon
appears larger than the Sun.
– If an eclipse occurs at that time, it will be a total eclipse.
• When the Moon is on the far side of its orbit, the Moon
appears smaller than the Sun and can't completely cover it.
– In this case the Moon's umbral shadow is not long
enough to reach Earth.
– Instead, the 'antumbral' or negative shadow reaches
Earth.
– The track of the antumbra is called the path of
annularity.
• It is all about the relative positions of the earth, sun, and
moon, since they all are moving.
•If you are within this path, you will see an eclipse where a
ring or 'annulus' of bright sunlight surrounds the Moon at
the maximum phase.
Annular Eclipse
OCCURRENCES
•
•
•
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•
•
•
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2010 Jun 26 Partial Asia, Aus., Pacific, w Americas
2010 Dec 21 Total Asia, Aus., Pacific, Americas, Europe
2011 Jun 15 Total S.America, Europe, Africa, Asia, Aus.
2011 Dec 10 Total Europe, e Africa, Asia, Aus., Pacific, N.A.
2012 Jun 04 Partial Asia, Aus., Pacific, Americas
2012 Nov 28 Penumbral Europe, e Africa, Asia, Aus., Pacific, N.A.
2013 Apr 25 Partial Europe, Africa, Asia, Aus.
2013 May 25 Penumbral Americas, Africa
2013 Oct 18 Penumbral Americas, Europe, Africa, Asia
2014 Apr 15 Total Aus., Pacific, Americas
2014 Oct 08 Total Asia, Aus., Pacific, Americas
2015 Apr 04 Total Asia, Aus., Pacific, Americas
2015 Sep 28 Total Pacific, Americas, Europe, Africa, w Asia
OCCURRENCES
•
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2011 Jan 04 Partial: Europe, Africa, c Asia
2011 Jun 01 Partial: e Asia, n N. America, Iceland
2011 Jul 01 Partial: s Indian Ocean
2011 Nov 25 Partial: s Africa, Antarctica, Tasmania, N.Z.
2012 May 20 Annular: Asia, Pacific, N. America
Annular: China, Japan, Pacific, w U.S.
2012 Nov 13 Total: Australia, N.Z., s Pacific, s S. America
2013 May 10 Annular: n Australia, Solomon Is., c Pacific
2013 Nov 03 Hybrid: e Americas, Atlantic, s Europe, Africa
2014 Apr 29 Annular: s Indian, Australia, Antarctica
2014 Oct 23 Partial: n Pacific, N. America
2015 Mar 20 Total: Iceland, Europe, n Africa, n Asia
Total: n Atlantic, Faeroe Is, Svalbard
2015 Sep 13 Partial: s Africa, s Indian, Antarctica
How does planetary
motion effect our ……
WHAT ARE TIDES?
• According to Webster, a TIDE is the periodic
variation in the surface level of the oceans and of
bays, gulfs, inlets, and estuaries, caused by
gravitational attraction of the moon and sun.
• Exactly how does the moon and sun influence the
depth of our waters on earth?
• It is really all about gravitational forces
IT’S ALL ABOUT FORCES
Differential Forces
• Consider a water molecule in the ocean.
• It is attracted gravitationally to the Earth, but it also
experiences a much smaller gravitational attraction to the
Moon
• This gravitational attraction to the Moon is not limited to
the water molecules, every object on and in the Earth is
affected.
• Tides occur because these forces are not uniform:
– some parts of the Earth are closer to the Moon than
other parts, and since the gravitational force drops off
as the inverse square distance, those parts experience a
larger gravitational tug from the Moon than parts that
are further away.
HOW IT WORKS
Differential Forces
The Larger the arrow, the larger the pull from the
moon
BODY DISTORTION
• In this situation, we say that differential forces act
on the the Earth.
• The effect of differential forces on a body is to
distort the body.
• The body of the Earth is rather rigid, so such
distortion effects are small.
• However, the fluid in the Earth's oceans is much
more easily deformed and this leads to significant
tidal effects.
• We may illustrate the basic idea with a simple model of a
planet completely covered by an ocean of uniform depth,
with negligible friction between the ocean and the
underlying planet.
• The gravitational attraction of the Moon produces two
tidal bulges on opposite sides of the Earth.
•The liquid at point A is
closer to the Moon and
experiences a larger
gravitational force than
the Earth at point B or
the ocean at point C.
• Because it experiences a
larger attraction, it is
pulled away from the
Earth, toward the Moon,
thus producing the bulge
on the right side.
•On the left side the
Earth is actually being
pulled away from the
water.
•This is because the
gravitational force
exerted by the Moon at
point B is larger than
that exerted at point C.
•This pulling away gives
us our bulge on the left
side
Then, as our idealized Earth rotates under these bulges, a
given point on the surface will experience two high and two
low tides for each rotation of the planet.
SOURCES
Tides
http://csep10.phys.utk.edu/astr161/lect/time/tides.html
Eclipse
http://www.mreclipse.com/Special/LEprimer.html
http://www.mreclipse.com/Special/SEprimer.html
Phases
http://www.enchantedlearning.com/subjects/astronomy/moon/Phases.shtml
Seasons
http://csep10.phys.utk.edu/astr161/lect/time/seasons.html
http://www.crh.noaa.gov/fsd/astro/season.htm