Earth, Moon, and Sun
Chapter 19
Voting Questions:
How many of you……
• would like to live where it is dark all the
time?
How many of you……
• would like to live where it is light all the
time?
How many of you……
• enjoy having four seasons?
How many of you……
• would like to travel into space?
How many of you……
• would like to go to the moon?
How many of you……
• would like to live on Mars?
How many of you……
• would like to live on Mars if it meant never
returning to Earth and seeing your family
and friends again?
• Ancient Egyptians were among the first people
to study the stars.
• The study of the moon, stars, and other objects
in space is called Astronomy.
• In past times people believed the Earth to be a
the center of the Universe and everything
revolved around us.
• The Earth rotates on its axis which is an
imaginary line that runs through the North and
South Poles.
• This axis is tilted to 23.5 degrees (the tilt of the
Earth on its axis changes from 24.5 degrees to
22.5 degrees on a 41,000 year time scale).
• Earth spinning on its axis is called its rotation
(this is how we have day and night).
• A point on the equator rotates at about 1,600
kilometers per hour (most commercial jets don’t
move this fast).
• As the Earth rotates eastward, the sun appears
to move westward across the sky.
• The side facing the sun is daytime and the side
not facing the sun is night time (no kidding Mr. J
we are not stupid). DEMO
• The Earth rotates on its axis about once
every 24 hours.
• The Earth also revolves around the sun.
• The movement of one object around
another is called revolution.
Harvard Question
• When are we closer to the SUN?
Summer or Winter
• One complete circle around the sun is called an
orbit.
• As the Earth circles around the sun it is not a
perfect circle. The orbit is elliptical (this
changes over time).
• The elliptical orbit of the Earth around the sun
changes on a 100,000 year time scale.
• There are 365 days a year, but actually it
takes the Earth 365.25 days to make one
orbit around the sun.
• So this is why we have leap year.
• What would happen if we did not have
leap year?
Earth has seasons because its axis
is tilted as it moves around the sun.
• The SOLSTICE occurs in December and
June.
• It is when the axis of the Earth is facing
towards or away from the sun.
• When this occurs the sun will be directly
over head at 23.5 degrees north or 23.5
degrees south
Halfway between the solstices,
neither hemisphere is tilted toward
or away from the sun.
This is known as an EQUINOX which means “equal
night”.
During the equinox the daytime and nightime are
about the same.
Vernal equinox occurs around March 21st, and the
autumnal equinox occurs around September
21st.
Phases, Eclipses, and Tides
Moons Facts
• It takes the moon 27.3 days to revolve around the Earth.
• The moon has an oval orbit around the Earth.
• The moon rotates on it’s axis once every 27.3 days.
• A day and a year on the moon is the same.
• The same side of the moon, the “near side” always faces
the Earth. The “far side” of the moon always faces away
from the Earth.
Phases of the Moon
• The phase of the moon you see depends
on how much of the sunlit side of the
moon faces Earth.
Eclipses
• When the moon’s shadow hit Earth or Earth’s
shadow hits the moon, an eclipse occurs.
• An eclipse occurs when an object in space
comes between the sun and a third object, and
casts a shadow on that object.
• There are 2 types of eclipses:
– Solar
– Lunar
Solar Eclipse
Lunar Eclipse
Tides
• What causes tides?
• Tides are the daily rise and fall of Earth’s waters on its
coastlines.
When the tide comes in the tide rises until the water on the
beach reaches the highest point. This is called HIGH
TIDE.
Then the tide will go out until it reaches the lowest part on
the beach. This is called LOW TIDE.
Tides happen regularly.
Tides occur in all bodies of water, but they are most
noticeable in the ocean and large lakes.
Spring Tides
• Twice a month the moon, Earth and
sun are lined up (During the full and
new moons).
• Their combined gravitational pull
produces the greatest range between
the high and low tide, called a SPRING
TIDE.
Neap Tides
• In between spring tides, at the first and third quarter of
the moon, the sun and moon pull at right angles to each
other.
• This produces a NEAP TIDE, a tide with the least
difference between low and high tide.
• During a neap tide the sun pulls some of the water away
from the bulge. This tends to “even out the water level
reducing the difference between high and low tides.
Tides
• Tides are caused by the interaction of the Earth , the
moon, and the sun.
• This occurs by the force of gravity.
• Gravity is the force exerted by an object that pulls other
objects toward it.
• As the distance between objects increase gravity
decreases.
The Effect of the
Moon’s Gravity
• The moon pulls on the side closest to it more strongly than it pulls on the
center of the Earth.
• This creates a bulge of water, called a tidal bulge, on the side of the Earth
facing the moon (Letter A).
• The water at point C is pulled toward the moon less strongly than Earth is
as a whole.
• This water is left behind to form a second bulge.
• So you have tidal bulges at A and C and along coastlines in these areas you
have high tides and the areas between the bulges are experiencing low
tide.
A
D
B
• As the Earth rotates different places on
the surface of the Earth pass through the
areas of the tidal bulges and therefore
experience the change in water levels.
The Daily Tide Cycle
• As the Earth rotates, once per day, people on or near the
shore experience high and low tides as they pass
through the tidal bulges.
• In most areas high tide occurs about 12 hours and 25
minutes apart in each location.
• As the Earth rotates eastern parts of the US pass
through the area of the tidal bulge before points farther
west. Therefore high tide occurs later the farther west
you go along a coastline.
• In some places there are 2 high tides and 2 low tides a
day.
• In other places, the range between the water level is
less dramatic. One set of tides may be so minimal that
there appears to be only one high tide and one low tide.
• This is common along the coasts of Texas and Florida,
due to the gradual slope of the ocean floor of the Gulf of
Mexico.
Factors that Affect Tide
• High tide in California on a certain day is not
necessarily the same height as the high tide in
Oregon farther up the shore.
• Landforms such as capes, peninsulas and islands
interrupt the water’s movements.
Monthly Tide Cycle
• The suns gravity affects the tides as well as the moon
even though it is much farther away.
• Sometimes the moon and sun pull together on the
Earth’s waters and at other times, they pull in different
directions.
• Changes in the position of the Earth, moon, and Sun
affect the height of the tides during a month.
Monthly Tide Tables
Even with the many factors involved
scientists are able to predict the tides
accurately for various locations.
Earth’s Moon
The Moon
• Ancient Greeks thought the moon was perfectly
smooth.
• It was not until 400 years ago that scientists
were able to study the moon more closely.
• In 1609 Galileo made his own telescope by
putting two lenses together and observed the
moon.
• Galileo observed features on the moon
called craters, highlands and maria.
• Craters are small round pits caused by
impacts.
• Galileo inferred some areas on the moon
were highlands or mountains.
• The moon also had dark, flat areas, which
Galileo called maria.
– The latin word for sea.
• Galileo thought that the maria might be
oceans on the moon.
• The maria are actually low, dry areas that
were flooded with molten material billions
of years ago.
Moon Landing July 20, 1969
• Neil Armstrong landed on the moon;
• “That’s one small step for man, one giant leap
for mankind.”
• He meant to say, “That’s one small step for a
man..”
• http://batesmotel.8m.com/
• Astronauts brought back samples to Earth.
• Later Astronauts could stay on the moon for days
instead of hours.
• On the first trip to the moon astronauts brought back to
Earth 382 kg of rocks to study.
• Much of what scientists know about the moon came
from the detailed study of these rocks.
• Scientists have determined that the moon has cooled
almost completely, unlike the Earth.
• Apollo astronauts circled the moon and took
pictures.
• Astronauts realized the far side of the moon is
rougher than the near side.
• 1998 the Lunar Prospector mapped the entire
moon from an altitude of only 100 km. The
Lunar Prospector found evidence that there is
frozen ice in the lunar soil near the poles.