MOON
PHASES, TIDES, OCEAN CURRENTS, AND SEASONS
Unit Overview
In this unit we will explore how the moon interacts
with Earth. We will also learn about the phases of the moon and how the Earth’s
positioning with the sun gives us seasons.
Motions of the Earth
When the motions of the Earth and the moon are
considered, they can be described separately, but scientists prefer to describe
their motions in relation to each other. The Earth revolves every 364 ¼ days
around the sun while rotating every 24 hours on its own axis. At the same time,
the moon revolves every 29 ½ days around the Earth and rotates on its axis in
27 ⅓ days. These events cause us to basically see the same side of the
moon. Gravitational attraction keeps the Earth in its orbit around the sun and
the moon around the Earth.
Gravity and Orbits
Phases
of the Moon
As the moon revolves around the Earth, the shape of
the moon appears to change. The varying shapes, lighted by reflected sunlight,
are called the PHASES of the moon.
When the moon is in between the sun and the Earth, the side of the moon facing
the Earth is not lighted. This is the NEW
MOON PHASE.
As the moon continues in its orbit around the Earth,
part of its lighted half becomes visible. As the size of the lighted portion
increases, the moon is WAXING. When
the lighted portion of the moon becomes a semi-circle it is in the FIRST QUARTER PHASE. The lighted
portion of the moon continues to increase in size until it appears as a full
circle. This is the FULL MOON PHASE.
As the moon continues in its revolution around the
earth after the full moon phase, the size of the lighted portion decreases so
less of it is visible to the Earth. This is called WANING. When the visible portion becomes a semi-circle again, this
is the LAST QUARTER PHASE. The moon
again moves between the Earth and the sun, and becomes a NEW MOON. The cycle of phases begins again.
For additional information on the Phases of the Moon click here https://en.wikipedia.org/wiki/Lunar_phase
Moon Phases (01:56)
Eclipses
Eclipses
and Conclusion (01:37)
All the bodies moving around the sun cast long shadows
into space. When one planetary or satellite body passes through the shadow of
another, an ECLIPSE occurs.
There are two types of eclipses which are named
depending on which body, the sun or the moon is blocked. The first is a SOLAR ECLIPSE. A solar eclipse happens
when the new moon comes directly between the sun and the Earth. The small inner
part of the shadow is called the UMBRA.
Only those in this portion of the Earth in this part of the shadow see a TOTAL SOLAR ECLIPSE. The larger, outer
shadow is called the PENUMBRA. Those
who view an eclipse from this part of the shadow see only a PARTIAL SOLAR ECLIPSE. Since the orbit
of the moon is tilted in relation to the Earth, an eclipse occurs only when the
new moon is directly between the Earth and sun. This is a rare occurrence and
never lasts more than seven minutes.
Solar Eclipses (01:02)
The second type of eclipse happens when the
Earth comes directly between the sun and the full moon. This is called a LUNAR
ECLIPSE and takes place when the moon passes through the Earth’s
shadow. When it passes through the umbra, the eclipse is total. When the moon
passes through the penumbra a PARTIAL LUNAR ECLIPSE occurs.
Since the shadow of the earth is much larger than the shadow of the moon, lunar
eclipses may last several hours.
Tides
Due to the close proximity of the moon to the Earth,
there is a gravitational attraction between the Earth and the moon. This was
first discovered in the late 1600’s by Sir Isaac Newton. According to Newton’s
Law of Universal Gravitation, the gravitational pull of the moon on the Earth’s
waters causes the daily changes in the level of the ocean’s surface. This rise
and fall of the ocean is called TIDES.
The gravitational pull of the moon is stronger on the side of the Earth that
faces the moon, and causes a bulge known as the DIRECT TIDE. A smaller bulge is also created on the opposite side
of the Earth, called the OPPOSITE TIDE.
Low tides are produced halfway between the two high tides because ocean water
flows away from those areas toward the areas of high tide. Since the Earth
rotates on its axis, the moon’s gravity affects different parts of the Earth at
different times of the day. Therefore, any given location has two high tides
and two low tides every 24 hours. Since the moon rises about 50 minutes later
each day, the high and low tides are also 50 minutes later each day.
THE TIDES
During the full moon and new moon phases, the sun and
moon are directly in line with the Earth. This causes higher than normal high
tides called SPRING TIDES.
During the first and third quarter phases of the moon,
the moon’s gravitational pull is partially cancelled by the sun’s gravitational
pull. This causes high tides to be lower than normal. These are called NEAP TIDES.
The
Moon and Tides (04:00)
For additional information on Tides click on this link
http://www.sailingissues.com/navcourse6.html
Ocean Currents
CURRENTS
are the predictable patterns of the movement of water. This movement can be on the surface or in the
depths of the ocean. SURFACE CURRENTS are mainly controlled
by the wind. Wind patterns are fairly
predictable therefore so are the currents.
Currents move warm and cold water around, affecting the climate. The Gulf Stream is the most known warm water
current. It moves warm water from the Gulf of Mexico up the eastern coast of
the United States. The California
Current is a cold water current and that brings cold water down the California
coast from Alaska.
Oceans: Surface Currents and Deep
Currents (02:27)
Convection in the Atmosphere and
Oceans (03:07)
Seasons
Because the Earth is tilted on its axis, a different
portion of the Earth’s surface is exposed to varying intensities of the sun’s
rays as it revolves in its orbit around the sun. These changes in the angle at
which the sun’s rays strike the earth’s surface and changes in the amount of
daylight is what causes the SEASONS.
When the North Pole is tilted away from the sun, the
sun’s rays fall on the Northern Hemisphere at a lower angle. This tilting
causes there to be fewer hours of daylight. The sun’s rays also deliver less
heat to the Earth’s surface because they must travel through more of the
atmosphere before reaching it. With the weaker the sun and fewer hours of
daylight the WINTER season takes
place. At the same time, the Southern Hemisphere is tilted toward the sun and
the sun’s rays fall at a higher angle. This causes there to be more hours of
daylight and more heat is delivered to the Earth’s surface. This is the SUMMER season.
On June 21st or 22nd of each year, the sun’s rays
strike the Earth at a 90 degree angle along the Tropic of Cancer. At this point
in the Earth’s orbit, the North Pole points toward the sun. This day is the SUMMER SOLSTICE, also known as the
first day of summer. The Northern Hemisphere experiences the most hours of
daylight on that day. On December 21st or 22nd of each year, the sun’s rays
strike the Earth at a 90 degree angle along the Tropic of Capricorn. The North
Pole is now pointing away from the sun. This day is the WINTER SOLSTICE, or the first day of winter in the Northern
Hemisphere. The least hours of daylight are experienced on that day.
On September 22nd or 23rd of each year, the sun’s rays
strike the Earth at a 90 degree angle along the equator. This day is the AUTUMNAL EQUINOX or first day of fall
in the Northern Hemisphere.
On March 21st or 22nd of each year, the sun’s rays
once again strike the Earth at a 90 degree angle along the equator. This day is
the VERNAL EQUINOX or the first day
of spring in the Northern Hemisphere. During both equinoxes the hours of
daylight and darkness are equal because the North Pole points neither toward
nor away from the sun.
Spring
the Summer Solstice (01:44)
|
Winter Solstice – First day of Winter |
|
Vernal (Spring) Equinox – First day of Spring |
|
Summer Solstice – First day of Summer |
|
Autumnal Equinox - First day of Fall |
Now answer questions 1 through 14.