Download Earth in Space

6th Grade Astronomy
KEY CONCEPTS
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How does Earth move in
space?
What causes the cycle of
seasons on Earth?
KEY TERMS
Astronomy
 Revolution
 Axis
 Rotation
 Calendar
 Solstice
 Equinox
 Orbit
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Earth moves through space in two major ways:
rotation and revolution.
The imaginary line that passes through Earth’s center
and the North and South pole is Earth’s axis. The
spinning of Earth on its axis is called rotation.
Earth’s rotation causes day and night.
As the Earth rotates eastward, the sun appears to
move westward. It is day on the side of the Earth
facing the sun. As Earth continues to the east, the sun
appears to set in the west. Sunlight cannot reach the
side facing away from the sun, so it is night.
It takes Earth 24 hours to rotate once.
We call that cycle a day.
http://www.learner.org/jnorth/images/graphic
s/mclass/jr/Day2/Day_Sol_Eq21_RevolvingEar
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In addition to rotating on its axis, Earth
travels around the sun.
Revolution is the movement of one object
around another.
One complete revolution of Earth around the
sun is called a year.
Earth follows a path , or orbit, as it revolves
around the sun.
Earth's orbit is a slightly elongated circle, or
ellipse.
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You might be surprised to know that a spot
on the surface of the Earth is moving at 1675
km/h or 465 meters/second.
That’s 1,040 miles/hour.
Just think, for every second, you’re moving
almost half a kilometer through space, and
you don’t even feel it.
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Want to do the calculation for yourself?
The Earth’s circumference at the equator is
40,075 km.
And the length of time the Earth takes to
complete one full turn on its axis is 23.93
hours.
So 40,075/23.93 = 1,675 km.
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The speed of the Earth’s rotation changes as
you go North or South away from the
equator.
Finally, when you reach one of the Earth’s
poles, you’re taking a whole day to just turn
once in place – that’s not very fast.
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Because you’re spinning around and around on
the Earth, there’s a force that wants to spin you
off into space; like when you spin a weight on a
string.
The force is inertia.
But don’t worry, that force isn’t very strong, and
it’s totally overwhelmed by the force of gravity
holding you down.
The force that wants to throw you into space is
only 0.3% the force of gravity. In other words, if
the Earth wasn’t spinning, you would weigh
0.3% more than you do right now.
What is rotation?
 Which direction does the
Earth rotate?
 What causes day and
night?
 What force wants to fling
you off into space?
 Is the Earth spinning
faster at the equator, or
at the poles?
 How long does it take the
Earth to revolve around
the sun?
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A calendar is a system of organizing time that defines the
beginning, length, and divisions of a year.
The ancient Egyptians created one of the first calendars.
Egyptian astronomers counted the number of days
between each first appearance of the star Sirius in the
morning.
They found out that there are about 365 days in a year.
Dividing the year into smaller parts was also difficult.
Early people used the moon cycles to divide the year.
The time from a full moon to the next is 29 ½ days. A year
of 12 of these adds up to 354 days.
The ancient Egyptian calendar had 12 months of 30 days
each with an extra 5 days at the end.
The Romans borrowed the Egyptian calendar.
The Earth orbits the sun in about 365 ¼ days.
The Romans adjusted the Egyptian calendar by
adding one day every four years.
 We know this fourth year as “leap year.”
 During a leap year February is given 29 days
instead of 28.
 Using this system makes sure that events such
as summer, occurs on the same date each year.
 The Roman calendar was off by a little more
than 11 minutes a year.
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Who invented the first known
calendar?
What star did they observe?
What was the problem with
this calendar?
How did the Romans adjust
the Egyptian calendar?
The sun hits the Earth from various angles. The
sunlight hits the Earth most directly near the equator.
At the poles, sunlight arrives at a steep angle. That is
why it is warmer near the equator.
 If the Earth’s axis were straight up and down relative
to its orbit, temperatures would remain constant
year-round. There would be no seasons.
 Earth has seasons because its axis is tilted as it
revolves around the sun.
 It is tilted as a 23.5 degree angle. As it revolves around
the sun, the north end is titled toward the sun for part
of the year and away from the sun the other part of
the year.
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Summer and winter are caused by the Earth’s
tilt as it revolves around the sun.
The change in season is not caused by
changes in the Earth’s distance from the sun.
In fact, Earth is farthest away from the sun
when it is summer in the Northern
Hemisphere.
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In June, the north end of Earth’s axis is tilted
toward the sun.
In the Northern Hemisphere the noon sun is
high in the sky and there are more hours of
daylight than dark.
The combination of direct rays and more
hours of sunlight heats the surface more in
June than any other time of the year.
It is summer in the Northern Hemisphere.
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At the same time south of the equator, the
sun’s energy is spread over a larger area.
The sun is low in the sky and the days are
shorter than the nights.
The combination of less direct rays and fewer
hours of sunlight, heats the Earth’s surface
less than any other time of the year.
It is winter in the Southern Hemisphere.
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In December, people in the Southern
Hemisphere receive the most direct sunlight,
so it is summer there.
At the same time, the sun’s rays in the
Northern Hemisphere are more slanted and
there are fewer hours of daylight.
So it is winter in the Northern Hemisphere.
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The sun reaches its greatest distance north or
south of the equator twice each year.
These days are known as a solstice.
The day when the sun is farthest north of the
equator is the summer solstice in the
Northern Hemisphere.
It is also the winter solstice in the Southern
Hemisphere.
This solstice occurs June 21 each year.
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It is the longest day of the year in the
Northern Hemisphere and the shortest day in
the Southern Hemisphere.
On December 21, the sun is farthest south of
the equator.
This is the winter solstice in the Northern
Hemisphere and the summer solstice in the
Southern Hemisphere.
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Halfway between the solstices, neither hemisphere is
tilted toward or away from the sun.
This occurs twice a year, when the moon is directly
overhead at the equator.
Each of these days is known as an equinox, which
means “equal night.”
During and equinox, day and night are about 12 hours
long everywhere on Earth.
The vernal (spring) equinox occurs around March 21
and marks the beginning of spring in the Northern
Hemisphere.
The autumnal equinox occurs around September 22.
It marks the beginning of fall.
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What are the two major motions of Earth as it
travels through space?
Which motion causes day and night?
What causes the seasons?
What are solstices?
What are equinoxes?
How are they related to seasons?
How would the seasons be different if the
Earth was not tilted on its axis?
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The changing relative positions of the moon,
Earth, and sun causes the phases of the
moon, eclipses, and tides.
The moon rotates once on its axis in the same
amount of time as it revolves around Earth.
A day and a year on the moon are the same
length.
For this reason, the same side of the moon
always faces Earth.
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The different shapes of the moon you see from
Earth are called phases.
The moon goes through a different set of phases
each time it makes a complete revolution around
Earth.
Half of the moon is always in sunlight.
The half of the moon that faces Earth is not always
the half that is sunlit.
The phase of the moon you see depends on how
much of the sunlit side of the moon faces Earth.
When the moon’s shadow hits the Earth or Earth’s
shadow hits the moon, an eclipse occurs.
 There are two types of eclipses: solar and lunar.
(solar and lunar come from the Latin words for “sun”
and “moon.”)
 A solar eclipse occurs when the moon passes
directly between Earth and the sun, blocking
sunlight from Earth. This happens during the new
moon phase.
 A solar eclipse occurs when the new moon blocks
our view of the sun.
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The very darkest of the moon’s shadow, the umbra
is cone-shaped.
From any point in the umbra, light from the sun is
completely blocked.
Only the people in the umbra experience a total
solar eclipse.
The larger part of the shadow is the penumbra. In
the penumbra, part of the sun is visible from Earth.
During a solar eclipse, people in the penumbra see
only a partial eclipse.
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A lunar eclipse occurs at a full moon when the Earth
is directly between the moon and the sun.
During a lunar eclipse the Earth blocks the sunlight
from reaching the moon.
Only during a full moon, because the moon is
closest to Earth’s shadow at that time.
Like the moon’s shadow during a solar eclipse,
Earth’s shadow has an umbra and penumbra.
Unlike a total solar eclipse, a total lunar eclipse can
be seen anywhere on Earth.
A partial lunar eclipse occurs when the moon passes
partly into the umbra of Earth’s shadow.
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During the 20th century 375 eclipses have
taken or will take place: 228 solar and 147
lunar. The last total eclipse of the sun visible
in the U.S. in this century occurred over the
state of Hawaii on July 11, 1991. The prior
such eclipse occurred over the state of
Washington on Feb. 26, 1979. The next total
eclipse will be visible from the U.S. in 2017.
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Tides- the rise and fall of ocean water that occurs every 12.5
hours.
The water rises for about 6 hours, then falls for about 6
hours.
Tides are caused mainly by differences in how much the
moon’s gravity pulls on different parts of the Earth.
At any one time there are two high tides and two places with
low tides on Earth.
As Earth rotates, one high tide stays on the side of Earth
facing the moon. The second high tide is on the opposites
side of Earth.
Each location on Earth sweeps through those tides every 25
hours.
The sun’s gravity also pulls on Earth’s waters.
The sun, moon, and Earth are nearly in a line during a new
moon.
 The gravity of the sun and moon pull in the same direction.
 Their combined forces produce a spring tide.
 This tide has the greatest difference between high and low.
 At a full moon the sun and moon are on opposite sides of the
Earth.
 This also causes a spring tide.
 It doesn’t matter the order in which they line up.
 Spring tides occur twice a month, at new moon and at full
moon.
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During the moon’s first quarter and thirdquarter phases, the line between Earth and
the sun are at right angles to the line between
Earth and the moon. The sun’s pull is at right
angles to the moons pull.
They are pulling in different directions,
producing the least difference between low
and high tides.
Neap tides occur twice a month.
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Think to yourself, what is the
difference between spring and
neap tides?
On your white board, draw a
Venn diagram comparing and
contrasting spring and neap
tides.
Using your white board as a
guide, discuss with your
neighbor the similarities and
differences of spring and neap
tides.
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The Greeks thought the moon was perfectly
smooth.
1609- Galileo Galilei made his own telescope
by putting two lenses in a wooden tube.
He was able to see details of the moon, that
had never been seen before.
Features of the moon include- maria, craters,
and highlands.
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The moon’s surface has dark, flat areas, which GaIileo called maria, the
Latin word for “seas.” Galileo thought the maria were oceans. He was
wrong.
The maria are hardened rock formed from lava flows that occurred
between 3-4 billion years ago.
The moon has many craters covering the surface.
Some craters are hundreds of kilometers across.
A long time ago scientist thought volcanoes caused these craters.
Today they know that meteoroids hitting the surface caused these holes.
Meteoroids are chunks of rock or dusk from space.
On Earth our craters have been worn away over time by water, wind and
other forces.
Since the moon has no liquid water or atmosphere, its surface has
changed very little over billions of years.
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Galileo correctly guessed that some of the
light colored features of the moon were
highlands, or mountains. The peaks of the
highlands and the rims of the craters cast
dark shadows.
The rugged lunar highlands cover much of
the moon’s surface.