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Water, Air, and Space General Concepts
1) Earth Science is the study of Earth and Space and the forces and processes that shape it. It includes four
major branches: meteorology, oceanography, astronomy, and geology.
2) Scientists have given names to the living, solid, liquid, and gas parts of the earth. The four spheres of
Earth Science are the Biosphere, Lithosphere, Hydrosphere, and Atmosphere.
3) The living part of the Earth is called the Biosphere. The term is used to refer to the whole earth.
Ecologists, Environmentalists, and other types Life Scientists study the Biosphere.
4) The lithosphere is the solid part of the earth. It is made up of rocks, minerals, and soil. The ground you
walk on is part of the lithosphere. Mountains are part of the lithosphere. The lithosphere extends under the
ocean and makes up the continents. It includes the earth’s crust and the top part of the upper mantle.
Various types of geologists study the lithosphere.
5) The hydrosphere is the liquid part of earth that is near or around the surface. About 71% of the earth’s
surface is covered by water. The amount of water on earth is immense, an estimated 326 million cubic miles.
A cubic mile of water equals more than one trillion gallons. However, 99.7% of all water on earth is
unusable by humans.
6) 97.2269% of the earth’s water is found in the oceans. Salt lakes, sometimes called inland seas, make up
0.008% of the earth’s water supply. Salt water is unusable by living organisms. The remaining 2.7651% is
classified as fresh water. However, most fresh water on earth is locked up in ice sheets and glaciers (2.14%)
so it is not usable by living organisms. Only 15% of the Earth’s freshwater can be used by living things. Of
the remaining water, 0.61% of the world’s supply is in the ground. This leaves only 0.009% for all the
world’s fresh water lakes and 0.0001% for rivers and streams. 0.005% of the water is found in soil moisture
(above the aquifer) and, 0.001% is found in the atmosphere.
7) Humans use an enormous amount of water. Each person uses about 80-100 gallons per day. In the year
2005, the United States used about 410,000 million gallons per day of fresh water. Water usage is broken
down into eight major categories. The following is what water was used for in 2005: thermoelectric power
= 49%, irrigation (farming) = 31%, public supply = 11%, industry = 4%, aquaculture (fish farms) = 2%,
domestic (self-supplied wells) = 1%, mining = 1%, livestock = <1%
8) All organisms need clean water for life processes. Water quality is a measure of the suitability of water for
a particular use based upon selected characteristics. Some include: chemical characteristics - pH,
dissolved oxygen, nitrates, phosphates, salts, hardness, iron, carcinogens, solvents, sediments, etc.; physical
characteristics - temperature, electrical conductivity, turbidity / suspended particulates (muddiness), etc.;
biological characteristics- bacteria such as fecal coliform, protozoa, pathogens, etc.
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9) Water pollution contains minerals, chemicals, or organisms that can disrupt life processes and cause disease
or death. The EPA (Environmental Protection Agency) has defined had defined water unsafe to drink as
having greater than 1000 ppm of contaminates. The largest source of water pollution is sediment - loose clay,
mud, or minerals that have been eroded. There are two types of pollution. Point source and nonpoint source
10) Point source pollution enters the water supply from a specific location which is known and is confined to
a relatively small area. Non point source pollution enters the water supply from a large area, and the exact
source or origin of the pollution is unknown.
11) An algae bloom is an area of water pollution. Pollution feeds the plant life in the water. The plants
overpopulate causing the germs that decompose them to overpopulate. The excess germs take the oxygen
out of the water causing animal life to die.
12) Acid rain is a type of both water and air pollution. Pollutants such as sulfur dioxide (SO2) or nitrogen
oxide (NOx) enter the air from a source such as a power plant or volcano. The wind blows the pollutions far
from the source. The pollutant lowers the pH (raises the acidity) of the water in the air. Pure water has a pH
of 7.0.
Normal rain is slightly acidic because carbon dioxide dissolves into it, so it has a pH of about 5.5.
As of the year 2000, the most acidic rain falling in the US has a pH of about 4.3 which is very harmful to plant
and animal life.
13) Although the percentage of fresh water available on earth is small, the earth never runs out because water
is a renewable resource. This means its actual amount is not limited and it can be easily replenished. This
happens because water can readily change from one state of matter (solid, liquid, gas) to another at the
temperatures and pressures that occur around Earth’s surface.
14) Water is constantly moving between each of the four spheres of Earth Science. This unending circulation
of earth’s water supply is called the water cycle or the hydrologic cycle. It has several main steps: water
storage, evaporation/transpiration, condensation, precipitation, and recharge of water storage.
15) Water storage supplies are stored in lakes, streams, oceans, and snow fields. Man-made water supplies
are called reservoirs. Water can also be stored underground in an area called an aquifer.
16) Evaporation is the process where liquid water is heated and becomes a gas called water vapor. Usually
the sun heats the water supply and vaporizes it at its surface. Transpiration is the process by which water is
evaporated into the air through plants (leaf pores).
17) Condensation is the process of changing water vapor (gas) held in the air into a liquid by removing heat cooling. Water drops on the outside of a cold glass are condensed water. The temperature at which water
vapor changes from a gas to a liquid is called the dew point or saturation point. When the dew point is close
(within 5ºF) to the air temperature, rain is very likely. Dew forms when moist air (water vapor) near the
earth’s surface cools. If the surface temperature falls below freezing, then the dew turns into frost.
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18) Humidity is moisture or water in the atmosphere. The amount of humidity is determined by temperature.
Higher temperatures mean higher humidity. Lower temperatures mean lower humidity.
19) Relative humidity is a measure of how much water air holds at a certain temperature compared to the total
amount of moisture that it can hold. It is measured in percent. When air is totally dry, the relative humidity
is 0. When air holds half the water that it is able, the relative humidity is 50%. When air is completely full
of water the relative humidity is 100%. When air reaches the point of 100% humidity, the air is saturated and
water vapor will change from a gas to a liquid and it will rain.
20) Fog is a mass of tiny liquid droplets of water that have condensed around dust particles (cloud seeds).
The droplets are too tiny to fall and are held in place by air currents. Fog forms on the ground when a layer of
air is cooled to its dew point by contact with the colder surface. Clouds are very similar to fogs only they
form at much higher altitudes. They are formed when a layer of moist air is cooled by another layer of air.
Clouds are not water vapor. They are liquid water droplets too tiny to fall to Earth as precipitation.
21) Precipitation is water that falls to earth from clouds in the atmosphere. There are five kinds: drizzle,
rain, sleet, snow, and hail. The size of water vapor droplets is very small. When water droplets cool and
condense, they get larger to the point that gravity pulls them to the earth. Drizzle droplets are much smaller
than rain droplets, but are much larger than water vapor droplets.
22) When water droplets freeze on their way to the earth, sleet, snow, and hail form. Sometimes strong
updrafts blow the droplets back up into the clouds where they gain another layer of water which refreezes. A
hailstone the size of a marble might have been blown up and fallen down over 25 times.
23) The recharge of water storage happens after precipitation hits the ground. It can happen above ground or
below ground. The water follows surface contour lines as it flows as runoff into lakes, rivers, and the ocean.
Much of the water that hits the ground does not runoff. It percolates or moves downward through the pores
and spaces in the soil until it hits the water table - a place where the soil is saturated or completely filled with
water. This zone of saturation is an underground water storage area called an aquifer. If it rains so much
that the water table moves to the surface, there will be a flood. If it rains so hard and fast that most of the rain
runs off above the ground and does not go into the ground, then flash flooding occurs.
24) The rate of movement of ground water depends on the porosity and permeability of the ground.
Porosity
is the amount of void space or opening in a rock or other earth material like a sand deposit. It is how much
water a material can hold. Porosity represents the storage capacity of the ground material. It is measured in
percent of open space. The more tightly packed the grains are, the lower the porosity. If the sizes of the
ground particles are both large and small, the smaller grains tend to fill the spaces between the larger grains,
resulting in lower porosity.
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25) Permeability refers to how well water flows through a material. It is controlled by how large the pores
are, and how well connected they are. Materials such as clay and shale may have a high porosity because of
lots of microscopic openings, but they have low permeability because the openings are not connected. So,
water cannot pass through. Materials such as clay and solid rock that block water are called confining units.
26) The water in the aquifer moves due to gravity and eventually recharges or refills wells, reservoirs, lakes,
rivers, and the ocean. This is how we get our water.
27) Weather is the day-to-day conditions of the atmosphere. It is caused by two main things: (a) the
unequal heating of the earth’s surface by the sun, and (b) the earth’s rotation on its axis.
28) The unequal heating is caused by the earth’s tilt and curvature. The earth’s rotation causes wind and
ocean currents. Some parts of the earth get hotter than others, and the heat is spread around by the
atmosphere.
29) The atmosphere is the area of gases that surrounds the earth. It is held to earth by gravity. The air you
breathe is part of the atmosphere.
30) Air is a colorless, odorless, and tasteless mixture of gases. It is matter and takes up space (mass and
volume). The atmosphere has the following ingredients:
nitrogen - 78% of the atmosphere; inert gas; dilutes oxygen; mostly useless for animals in its
pure form; bacteria “fix” nitrogen and turn it into nitrates and nitrites which are used by plants and
animals to make proteins and DNA
oxygen - 20% of the atmosphere; used by plants and animals for respiration - breathing and making
food; includes ozone - a poisonous bluish form of oxygen with a strong odor; when ozone is
produced on the ground from cars and factories, it is harmful and forms smog; from the middle to the
top of the stratosphere is the ozone layer; the ozone layer acts like a shield that absorbs the sun’s
ultraviolet (UV) energy which is destructive to life and causes cancer.
water vapor - varies between 1 to 4% of the atmosphere; heavy greenhouse gas; absorbs heat
argon - 1% of the atmosphere; inert gas; used in welding
carbon dioxide CO2 - 0.04% of the atmosphere; produced when materials burn (combustion) and
when humans and animals breathe out (respiration); heavy greenhouse gas; absorbs heat
methane, hydrogen, CFC’s - trace greenhouse gases, less than 1 % of the atmosphere
helium, neon, krypton, xenon - other inert trace gases, less than 1 % of the atmosphere
31) The atmosphere has five main layers which are identified mainly by their change in temperature but also by their
pressure/density, and content. The atmosphere extends out about 41,000 miles from earth’s surface to outer space, but
most of the air is concentrated into the bottom two layers (troposphere and stratosphere - 0 to 30 miles above the ground)
due to gravity. The layers beginning from the surface are: troposphere, stratosphere, mesosphere, ionosphere (lower
thermosphere), exosphere (upper thermosphere).
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32) Heavier gases separate from lighter ones and are near the surface. Different gases absorb different
amounts and types of solar energy. This is why the temperatures change through the layers. From the
ground, the temperature first decreases, then increases, then decreases, then increases, then decreases to outer
space. Each layer has a top part, called a pause, where the temperature stays the same for a distance.
33) The troposphere is about 5-11 miles deep (26,000 to 60,000 ft). It is the layer closest to earth and
contains most of the air. The troposphere is where weather happens. Temperatures drop as you move away
from the earth (go higher). The top part of the troposphere is called the tropopause. It acts like a lid to keep
water vapor and other heavy greenhouse gases in the troposphere. The temperature stops dropping and
remains at -76°F.
34) The earth’s atmosphere spreads out the heat from the sun, so the earth has an even temperature. The
worldwide average temperature on the ground or standard atmospheric temperature is 59°F or 15°C
35) The greenhouse effect is the trapping of heat by the tropopause. Life on earth could not exist without it.
Radiant energy is both absorbed by the ground and reflected back to the atmosphere. Heavy greenhouse
gases in the troposphere such as carbon dioxide, water vapor, and methane absorb the reflected infrared rays
and reflect them back to earth. In this way, much of the heat is trapped like a blanket. The amount of energy
trapped depends on the contents of the troposphere.
36) Venus has a much thicker atmosphere causing its average temperature to be almost 900°F, while Mars has
a much thinner atmosphere causing its temperature to be around -81°F.
37) Adding extra gases such as CO2, ozone, methane, and CFC’s from car exhaust fumes and factory
emissions increases the amount of trapped energy in the troposphere. Global warming, sometimes called the
enhanced greenhouse effect, refers to the increase in global average temperature potentially due to human
activity. A rise in global temperatures could mean higher sea levels, less land, different vegetation - direct
impact on human civilization. There are extremist positions that people take on both sides of the issue of
global warming. Some think that human beings have totally caused the recent rise in global temperatures,
while some think that humans have not had an effect at all on climate change.
38) There are three ways that heat travels on earth.
(a) conduction - heat moves from direct contact between two or more objects
(b) radiation - heat moves with no contact between objects
(c) convection - heat is carried between objects by a medium (liquid or gas)
39) Most energy on earth travels in convection currents. A convection current is a moving wave of liquid
(water) or gas (air) caused by heat spreading molecules apart. Heat energy causes a liquid or gas to rise
because it gets lighter. As the heat is slowly lost, the molecules get cooler and heavier and sink. This
movement causes currents.
40) All winds on earth are convection currents. They move vertically (up and down)
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when warm low pressure (lighter/less dense) air rises and cooler high pressure (heavier/more dense) air sinks.
Winds move horizontally (side to side) because of the earth’s rotation. Winds are always described by the
direction they come from!
41) Convection cells are large bodies of moving air. They are global wind patterns that are named for the
direction they come from.
42) The Coriolis Effect is the cause of worldwide wind patterns in which winds are deflected and move to the
right in the northern hemisphere and move to the left in the southern hemisphere.
43) The Coriolis Effect is caused by the earth’s rotation. Cool air from the polar regions sink down while
warm air from the equator rises. The rotation causes the winds to be deflected. Six distinct global wind
patterns are formed from the Coriolis effect- three on each hemisphere.
(a) polar easterlies (60° to 90°)
(b) westerlies (30° to 60°)
(c) east trade winds (0° to 30°)
44) The horse latitudes are at 30 latitude in both hemispheres. Because it is the area between convection
cells, there is no horizontal wind here. Winds sink straight down. The doldrums are at the equator - 0°.
Because it is the area between convection cells, there is no horizontal wind here. Winds rise straight up.
45) Jet streams are often called rivers of air. They are narrow bands of strong wind found at the top of the
troposphere. Their paths typically have a meandering or winding shape. The width of a jet stream is
typically a few hundred miles and its vertical thickness often less than three miles. Jet stream winds usually
have a speed of 150 to 300 miles per hour, but speeds up to 450 miles per hour have been recorded. In the
northern hemisphere jet stream winds blow from west to east but the flow often shifts to the north and south.
The location of jet streams shift throughout the year and they are said to "follow the sun" since they move
north with warm weather and south with cold weather. Jet streams are also stronger in the winter because there
is a large contrast between colliding arctic and tropical air masses. In the summer, the temperature difference
is less extreme between the air masses and the jet stream is weaker. One of the most important impacts of the
jet stream is the weather it brings. Because it is a strong current of rapidly moving air, it has the ability to push
weather patterns around the world. As a result, most weather systems do not just sit over an area, but they are
instead moved forward with the jet stream. The position and strength of the jet stream then helps
meteorologists forecast future weather events. In addition, they are important to air travel because flying in
or out of them can reduce flight time and fuel consumption. One future benefit of jet streams could be to
power airborne wind turbines.
46) Two main jet streams affect weather in North America, the polar jet and the subtropical jet. The polar jet
stream is found between 23,000 to 39,000 feet above the ground and is located between 30° to 60° north
latitude. It has the strongest winds. The subtropical jet stream has lower wind speeds and is located at
around 33,000–52,000 feet above the ground at 30° north latitude.
Stop!
Pretest A covers only concepts 1-46
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47) El Nino is a climate event where a tropical South Pacific ocean current found around the equator and
countries of Peru and Chile warms a few degrees. It is a convection current, not a storm. An El Nino cycle
lasts about one calendar year and occurs about every 3 to 7 years, but they are beginning to happen more often.
During an event cycle, ocean temperatures rise a couple degree causing sea levels to rise. Trade winds are
weakened and even reversed. Heated water means more precipitation; more rain effects global wind patterns.
48) El Nino cycles disrupt the jet stream in North America causing unusual weather. El Nino cycles are even
responsible for monsoons in the far East and droughts in Africa. El Nino cycles predate human industrial
activity. La Nina is the normal condition where the South Pacific ocean is cool.
49) The Gulf Stream is a strong, fast moving, warm ocean current that originates in the Gulf of Mexico and
flows into the Atlantic Ocean. It is generally contains very warm, deep, and narrow currents that carry water
from the tropics to the poles. The Gulf Stream was first discovered in 1513 by the Spanish explorer Juan
Ponce de Leon and was then used extensively by Spanish ships as they travelled from the Caribbean to Spain.
In 1786, Benjamin Franklin mapped the current, further increasing its usage. The Gulf Stream, like all other
ocean currents is mainly caused by wind as it creates friction when moving over the water. This friction then
forces the water to move in the same direction.
50) Because ocean currents circulate water of different temperatures all over the globe, they often have a
significant impact on the world’s climate and weather patterns. The Gulf Stream is one of the most important
currents in this regard since it gathers all of its water from the warm tropical waters of the Caribbean and the
Gulf of Mexico. As such, it keeps sea surface temperatures warm, causing the areas around it to be warm and
more hospitable. Florida and much of the Southeastern United States for instance is mild all year round.
51) The greatest impact the Gulf Stream has on climate is found in Europe. Since it flows into the North
Atlantic Current, it too is warmed (though at this latitude the sea surface temperatures are cooled
considerably), and it is believed that it helps keep places like Ireland and England much warmer than they
would otherwise be at such a high latitude. The Gulf Stream and its warm winds are also responsible for
keeping northern Norway’s coast free of ice and snow. As well as keeping many places mild, the Gulf
Stream’s warm sea surface temperatures also aid in the formation and strengthening of many of the hurricanes
that move through the Gulf of Mexico. Additionally, the Gulf Stream is important to the distribution of
wildlife in the Atlantic. The waters off of Nantucket, Massachusetts for example are incredibly biodiverse
because the presence of the Gulf Stream makes it the northern limit for southern species varieties and the
southern limit for northern species.
52) The stratosphere is about 20 miles thick. It starts at about 10 miles or 60,000 feet above the ground and
goes to about 30 miles or 160,000 ft above the ground. Temperatures start to increase through this layer.
They start at about -76°F and increase to about 40°F in the stratopause (top part). The stratosphere has very
thin air made mostly of oxygen.
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53) From the middle to the top of the stratosphere is the ozone layer. The reason the sky looks blue is because
of the ozone layer. Ozone is a poisonous bluish gas with a strong odor. It is a molecule made of three
oxygen atoms (O3). The ozone layer acts like a shield that absorbs the sun’s ultraviolet (UV) energy which is
destructive to life and causes cancer.
UV hits O3 breaking it into O2 and O; UV hits the O2 and O and combines them again into O3
54) When ozone is produced on the ground from cars and factories, it is harmful and forms smog. Pollutant
such as chlorofluorocarbons (CFC’s) from factories, refrigerators, and air conditioners rise through the
atmosphere. The chlorine in the CFC molecule attacks the ozone molecule destroying it. When the
molecules in the ozone layer are broken apart (from above by the sun and below by pollution), the layer is
thinned allowing more harmful UV rays to reach the earth. The thin areas are sometimes called holes.
55) There are different temperatures on earth because all parts do not get the same amount of radiant energy
from the sun. This difference in radiant energy is caused from sunlight striking the earth at different angles.
The different angles are causes by the tilt and curvature.
56) Sunlight at the equator hits the earth at 90° or straight on. This means all the energy is concentrated or
focused directly on this area. higher angle = less area = more radiant energy = more heat energy = highest
temperatures
57) Sunlight at the polar regions hits at a very low angle. Most radiant energy skims by without touching and
is not concentrated in any one spot.
58) When referencing the earth, always look down from above. The earth spins counterclockwise on its axis
(north and south poles). This is why the sun always rises in the East and sets in the West. One rotation on its
axis is called a day (about 24 hours). The earth also revolves around the sun in a counterclockwise direction
when looking down from above. One rotation is called a year (about 365 days).
59) Seasons are periods of time within a year when the temperature stays about the same. A change in the
season means a change in temperature. Seasons are caused by the tilt of the earth as it goes around the sun.
60) The earth’s tilt affects (a) temperature variation in one spot in one year - seasons; the greater the tilt, the
larger the variation (b) amount of daylight (c) climate regions
61) Our earth is currently tilted at about a 23.5° angle. During some parts of the year, the tilt leans toward the
sun (summer). During some parts the year, the tilt leans away (winter). Seasons are opposite in the northern
and southern hemispheres.
62) The earth’s tilt is currently decreasing. A 40,000 year cycle will bring the tilt from 24.5° to about 21.5°.
A greater tilt means hotter summers (and colder winters), because the added heat is trapped by the
atmosphere. So, global temperatures increase as the tilt increases, and ice ages match up with a lower tilt.
Paeloclimatology uses ice core samples, tree rings, coral reefs, and various other methods to study the history of earth’s
temperature. Studies show that the earth’s climate both rises and decreases over long cycles.
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63) There are three distinct climate regions caused by the tilt – tropics, temperate, and polar. Climate is a
combination of temperature and precipitation over an area. The tropics are around the equator between 23.5°
south and 23.5° north latitudes. The tropic of Cancer is 23.5° north latitude, and the tropic of Capricorn is
23.5° south latitude. There are no seasons in the tropics. Every day gets about 12 hours of sunlight (exactly
12 at the equator).
64) The temperate climate regions are between 23.5º and 66.5º. There are distinct seasons here. The sub
tropics are part of the temperate region. They have mild seasons and are mostly dry. They are between
23.5º and 35º.
Central Ohio is about 40º north latitude. The polar regions are between 66.5º and 90º
latitude. There are no seasons here. It is always cold and dry. The arctic circles are 66.5º latitude.
65) On June 21st (the summer solstice) the northern hemisphere leans the most toward the sun. There are
more hours of daylight on this day than any other. Ohio latitudes receive about 14-16 hours of daylight.
The north polar climate regions receive 24 hours of daylight this day, and the tropics 12 hours.
66) On December 21st (the winter solstice) the northern hemisphere leans the most away from the sun. There
are fewer hours of daylight on this day than any other. Ohio latitudes receives about 7-10 hours of daylight.
The north polar climate regions receive 0 hours of daylight and the tropics 12 hours.
67) On March 20 or 21 (the Spring or Vernal equinox) and September 22 or 23 (the Fall or Autumnal
equinox), the earth’s axis not leaning toward or away from the sun. On these days, all parts of the earth
receive 12 hours of daylight and 12 hours of darkness. Ohio gains or loses between 5 ½ and 7 ½ minutes of
daylight every day.
68) The earth averages 93 million miles from the sun. On July 3-4 the earth is at its farthest distance from the
sun at 94.5 million miles, called the aphelion. On January 2-3, the earth is at its closest point to the sun at
91.5 million miles, called the perihelion. For this reason, the southern hemisphere of earth tends to have
hotter summers and colder winters, while the seasons in the northern hemisphere (United States) are not as
harsh as those in the south (Australia).
69) The average distance between the earth and the moon is about 240,000 miles. The orbit of the moon
around the earth is an ellipse (a circle with two centers), so the distance is not constant. The point in orbit
where the moon is farthest from the earth is called the apogee. This distance is about 254,000 miles. The
point in orbit where the moon is closest to the earth is called the perigee. This distance is 227,000 miles.
70) If viewed from above the north pole, the earth rotates counterclockwise on its axis and orbits
counterclockwise around the sun. The moon also rotates counterclockwise and orbits counterclockwise
around the earth. However, they travel and rotate at much different speeds. The earth orbits the sun at about
66,620 mi/hr while the moon obits the earth at the speed of only about 36 mi/hr
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71) The moon is about 1/4 the size of earth and has about 1/6 the gravity. Earth’s gravity holds the moon in
orbit and controls the rate at which it spins. Because the rotation and revolution of the moon take the same
amount of time, 27.3 days, observers on the earth always see the same side of the moon. Astronomers call
this captured rotation.
72) Because of captured rotation, there is a side of the moon which no one on earth ever sees. Often called
the far side of the moon or the dark side of the moon, this region was first seen by a Russian spacecraft in
1959.
73) The moon shines by reflecting sunlight from its surface. Half of the moon is lighted while the other half
is dark. As the moon revolves around the earth, you see different portions of its lighted side, causing its
appearance to change.
74) Moon phases are the
changing appearances of the
moon as seen from the earth.
The phase you see depends on
the relative positions of the
moon, Earth, and sun. One
moon phase lasts 29 calendar
days, 12 hours, 44 minutes, and
29 seconds, or 29.5 days.
75) A moon phase or month
begins with a new moon. A
new moon occurs when the
lighted half of the moon is facing
the sun and the unlighted side
faces the earth. The moon is in the sky, but cannot be seen because there is no light reflecting from it onto us.
76) As the moon continues its orbit around the earth, part of its lighted half becomes visible. When the
visible portion of the moon is increasing, the moon is in its waxing phases.
77) When a sliver of the moon becomes visible from the earth, the moon enters the waxing crescent phase.
78) When the moon has moved through one quarter of its orbit after the new moon, half of the lighted side is
facing the earth. This is called the first quarter phase. When the visible portion on the moon is larger than a
semi-circle and is still increasing, the moon is in the waxing-gibbous phase.
79) At a full moon the earth is between the sun and the moon. The entire lighted side of the moon is seen
from the earth.
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80) After the full moon phase, the portion of the moon visible from the earth deceases. This is called the
waning phases of the cycle.
81) The moon moves through the waning gibbous phase, last quarter phase or third quarter phase, and waning
crescent phase until none of the lighted portion faces the earth, and a new moon appears to start another cycle.
82) Although the moon revolves around the earth in 27.3 days, a longer period of time is needed for it to go
through a complete cycle of phases. The period from one new moon to the next is 29.5 days. This 2.2 day
difference is due to the orbiting of the earth-moon system around the sun. In the 27.3 days in which the moon
orbits the earth, the two bodies move slightly farther along in their orbit around the sun. Therefore, the moon
must go a little farther to get directly between the earth and the sun. This is the position of the moon in the
new moon phase. About 2.2 days are needed for the moon to travel this extra distance and catch up with the
earth.
83) The phrase “once in a blue moon” means not very often. It comes from the fact that every 2.5 years one
month will have a second full moon called a blue moon. This happens because each month has more time
than it takes to complete one moon cycle.
84) When something is eclipsed, it is blocked, or its view is obscured. An eclipse occurs when the earth or
moon temporarily block sunlight from reaching the other causing a shadow on one. They can only occur
when the sun, the moon, and earth are perfectly lined up.
85) A solar eclipse occurs when the moon moves directly between the sun and the earth blocking sunlight and
casting a shadow on part of the earth. Only the outer portion of the sun’s atmosphere is visible at this time.
Only a small area of the earth experiences a total solar eclipse. A person must be within the shadow region to
see the eclipse, so they are difficult to see. A total solar eclipse occurs up to twice a year.
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86) A lunar eclipse occurs when the earth moves in between the moon and sun. The earth’s shadow falls on
the moon. The moon may appear dark red. Lunar eclipses also occur twice a year, but they are much easier
to see than a solar eclipse because anyone on the night time side of earth can see the lunar eclipse. Lunar
eclipses may last several hours, much longer than a solar eclipse, because the earth casts a much larger shadow
than the moon.
87) If the plane of
rotation of the
earth and the moon
were lined up
exactly, solar and
lunar eclipses
would happen
every month.
However, the orbit
of the moon is
tilted at a 5º angle to the plane of the earth and sun.
88) The daily changes in the level of the ocean surface are called tides. Tides are caused by the gravitational
pull of the moon and the sun, but primarily the moon since it is closer. The moon’s pull is strongest on the
part of the earth directly facing the moon. The moon’s gravity actually pulls the earth’s water as it orbits the
earth causing a slight bulge. The water on the opposite side of the earth also bulges. This is called a high
tide. The area 90º to the tides, where the water is drawn away from, is called low tide. There are two high
tides and two low tides on earth each day.
89) Since the earth rotates, different parts of the water face the moon daily which causes the tides to keep
changing. The difference between high tide and low tide is called a tidal range.
90) Lakes also have tides, but the changes are very small. Lake Superior has a tidal range of only 5 cm.
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91) If the earth and moon did not move, tides would always occur in the same locations. Since the earth
rotates from west to east, tidal bulges appear to move westward around the earth. Because there are two tidal
bulges, high tides and low tides are less than a day apart.
92) The sun also affects the tides. When the sun, moon, and Earth are in alignment, there is a greater
gravitational pull. High tides are higher, and low tides are lower. This alignment is called spring tide. It
occurs every 14 calendar days, or during the full moon and new moon.
93) When the sun, moon, and Earth are at a 90º angle, gravitational forces work against each other so the tides
are lower. This is called neap tide. It occurs half way between the spring tides during first quarter moons
and last quarter moons.
94) One low tide-high tide cycle takes 12 hours and 25 minutes. A daily cycle of two highs and lows, a tidal
day, takes 24 hours and 50 minutes. A tidal day is the time period between two successive passes of the
moon over a point on the earth.
95) While the earth turns, the moon is also moving eastward along its orbit about the earth. Like the sun, the
moon appears to rise in the east and set in the west. The earth’s rotation brings the moon into view every day.
After 24 hours, the earth point that began directly under the moon is no longer directly under the moon. The
earth must turn another 12º, requiring an additional 50 minutes, to bring the starting point on earth back in line
with the moon. In other words, as the moon
revolves around the earth, the earth must rotate
through more than one complete rotation to
catch up with the moon. As a result, the moon
rises and sets a little later each day. The earth
must rotate 24 hours and 50 minutes to bring the
moon back into the same position, so the moon
rises 50 minutes later each day. This explains
why tides arrive at any location about one hour
later each day.
96) The earth’s rotation speed is not constant.
Right now the earth’s rotation is slowing down.
This is caused by the friction of the ocean tides
rubbing against the continents. On average the
earth’s rotation is slowing 1/500th second each
day. Every 500 days, we lose one second.
Stop!
Pretest B covers
only concepts 47-96