Earth, Moon, and Sun
Chapter 19
Earth in Space 19-1
• Astronomy is the
study of objects
beyond the Earth’s
atmosphere.
• It is one of the oldest
sciences, as ancient
people studied the
heavens for
agricultural an
religious reasons.
Rotation
• Ancient astronomers thought
that the sun, moon, and stars
were moving around the
Earth.
• This is because of the Earth’s
rotation.
• The Earth spins on its axis,
an imaginary line that passes
through the center of the
planet and both poles.
Axis
• The Earth spins on its
axis at about 1,600
km/hour at the
equator.
• The axis is currently
pointing toward the
star Polaris, the North
Star.
Day and Night
• Rotation causes the
Earth to have day and
night.
• It takes about 24 hours
for the Earth to rotate
on its axis once. We
call this 24 hour cycle
a day.
Tilt
• The Earth’s axis is
tilted 23.5° from the
vertical.
• The tilt is always
towards the North
Star, so part of the
year the north axis is
pointed towards the
sun, and part of the
year it is pointed
away.
• This causes the Earth
to have seasons.
Earth’s Seasons
• The Equator is warmer
because it receives
sunlight more directly than
the poles.
• Without the tilt Earth
would not have seasons.
• Summer and winter are
not affected by changes in
Earth's distance from the
sun. In fact, when the
Northern Hemisphere is
having summer, Earth is at
its greatest distance from
the sun.
Revolution
• Revolution is the
movement of one object
around another.
• One complete revolution
is called a year.
• The path around the object
is called an orbit.
• The Earths orbit is a
slightly flattened circle
called an ellipse. It travels
at 30-km/sec.
Calendars
• The Earth’s year is
365.25 days. That is
why our calendar has a
leap year every four
years.
• Calendars were
originally made to
make astronomical
predictions.
Lunar Calendars
• The moon revolves
around the Earth every
27.3 days.
• This is why people
that use lunar
calendars will have
years with 12 or 13
months.
Solstices
• Sun is directly at 23.5°
north or south latitude.
• Summer (June 21) solstice
is the longest day in the
Northern Hemisphere.
• The winter solstice
(December 21) is the
shortest day in the
Northern Hemisphere.
• Of course these are
reversed if you live in
Australia!
Equinoxes
• Means “equal night.”
Days and nights are equal
in time.
• Vernal equinox (spring)
occurs around March 21st.
• Autumnal equinox occurs
around September 23rd.
• Again if you lived in the
Southern Hemisphere
these would be reversed!
Phases, Eclipses, and Tides
19-2
Motions of the Moon
• The moon rotates on its
axis. Its period of rotation
equals its time to revolve
around the Earth.
• So we always see the
same side of the moon.
• The far side (dark side) of
the moon remained a
mystery until 1959 when
the Russian space probe
Luna 3 took the first
pictures of it.
Phases of the Moon
• The Moon goes through its entire set of phases once 29.5
days.
• The phase depends on how much of the sunlit side is
visible from the Earth.
• Waxing moons are showing us more of the sunlit side
(getting bigger), while waning moons are showing us less
of the sunlit side (getting smaller).
Visual Phases
Eclipses
• Eclipses occur when the Earth’s shadow hits the
moon, or the moon’s shadow hits the Earth.
• Since the moon’s orbit is slanted at 5°, we do not
get an eclipse every month.
Moon’s Shadow
• The umbra is the
darkest part of the
moon’s shadow. This
narrow cone just
reaches the surface of
the Earth.
• The penumbra is the
wider, less dark
portion of the shadow.
Solar Eclipses
• Solar eclipses occur when
the moon passes between
the Earth and the sun.
• This blocks sunlight from
a small portion of the
Earth.
• The moons shadow hits
the Earth.
• So a solar eclipse is really
just a new moon that
blocks your view of the
sun.
Total Solar Eclipse
• Light from the sun is
completely blocked by
the moon.
• The sky will be dark.
• You can see stars and
the solar corona,
which is the faint outer
atmosphere of the sun.
Partial Solar Eclipse
• Part of the sun will be
visible as the Earth
passes through the
moon’s penumbra.
Lunar Eclipses
• Occurs at a full moon
as the Earth passes
between the moon and
the sun.
• The Earth blocks
sunlight from the
moon.
• The moon is in the
Earth’s shadow.
Total Lunar Eclipses
• Total eclipses occur when
the moon passes into the
Earth’s umbra.
• You see the Earth’s
shadow on the moon
before and after the
eclipse.
• Unlike a solar eclipse,
they can be seen anywhere
the moon is visible.
Partial Lunar Eclipses
• Most of the time the
earth, moon, and sun
are not in a perfect
straight line.
• Only part of the moon
is in the Earth’s
umbra.
Tides
• Tides occur because of
the differences in how
much the moon (and
sun) pull on different
parts of the Earth.
• Most places will see
two high and two low
tides per day.
Rockets and Satellites
19-3
Rockets
• Rockets rely on
Newton’s Third Law
of Motion.
• They throw hot gases
out the back very
quickly (Force = mass
x acceleration).
• The equal but opposite
reaction pushes the
rocket forward.
How Rockets Fly
• Just as bottle rockets
fly by throwing water
out the back quickly,
and balloons fly by
throwing air out the
back quickly, NASA’s
rockets fly by
throwing hot gases out
very, very quickly!
Multistage Rockets
• Rockets are
limited by the
fuel they can
carry.
• Multistage
rockets can carry
more payload as
the empty stages
drop off, allowing
the remaining
engines to lift less
mass into orbit.
Artificial Satellites
• A satellite is any
natural or artificial
object that revolves
around (orbits) another
object in space.
• In 1957 the Russians
started the Space Race
by putting the first
satellite in orbit,
Sputnik 1.
Satellites
• Satellites are used
extensively today in
communications,
television, weather
forecasting,
astronomy,
atmospheric research,
navigation (GPS), and
by the military.
Geosynchronous Orbits
• These satellites
revolve around the
Earth at the rate as the
Earth rotates.
• So they appear to stay
in one place in the sky.
• They are usually used
for weather and
television.
Space Stations
• Large satellites in
which people can live
for long periods.
• The Salyut 1 was the
first, launched in
1971.
• Skylab was launched
in 1973 and used for
research.
Mir
• Mir was the first long term
space station. Launched
in 1986, it was visited by
astronauts from all over
the world.
• It pioneered the study of
the long term effects of
weightlessness on the
human body.
• It was finally de-orbited in
2001.
ISS
• Occupied since October
2000, it is the largest
station ever orbited.
• Designed for 7 occupants,
it is currently limited to
two because of problems
with America’s space
shuttle fleet.
• It is truly international, as
many countries are
building components for
it.
• Will be used for research
when the space lifeboat is
operational.
Space Shuttles
• First truly reusable
spacecraft.
• Five have been built, but
two have been lost in
accidents.
• Capable of reaching low
Earth orbit.
• Usually carries a crew of
7.
• Will be retired in 2010
after completing the US
portion of the ISS.
Earth’s Moon
19-4
The Moon
• There is no atmosphere on the
moon.
• Temperatures on the surface
range from over 100°C to
-170°C.
• To survive on the moon the
astronauts had to wear bulky
spacesuits to keep them warm
and carry their oxygen. These
suits weighed as much as the
astronauts themselves.
• But because the moon’s gravity
is only 1/6th of the Earth’s, they
could move around very easily.
• The moon is about 384,400-km
(240,000-mi) from the Earth.
Structure of the Moon
• Diameter is about 3,476-
km, a little less than the
distance across the USA.
• This is 1/4th the Earth’s
diameter, but the moon
has only 1/80th the mass of
the Earth.
• Since the Moon’s average
density is about the same
as the Earth’s outer layers,
it is believed the moon
lacks a dense core.
Origin of the Moon
• While there have been
many ideas, the theory
that best fits the
evidence is the collision
theory.
• About 4.5bya, when the
Earth was very young,
an object the size of
Mars collided with the
Earth. Lots of material
from the outer layer was
flung into orbit, where
it eventually combined
to form the moon.
Features of the Moon
• The early Greeks
thought the moon was
perfectly smooth.
• Galileo was first to use
a telescope to study
the moon.
• He saw that the moon
had craters, highlands
and maria.
Craters
• Caused by impacts
from meteoroids.
• Some are hundreds of
kilometers across.
• Many are named after
famous scientist from
long ago.
• Tycho is the bright
crater at the bottom of
the picture to the right.
Highlands
• Mountainous areas
covered with craters.
• Apollo 15 landed near
the Apennine
Mountains in 1971.
Maria
• Large, dark, flat areas.
• Maria is Latin for
“seas.”
• Galileo thought that
they might be oceans.
• They are low, dry
areas that were
flooded with molten
material billions of
years ago.
Rilles
• Are meandering, valley
like structures.
• Thought to be the remains
of collapsed lava tubes or
extinct lava flows. They
usually begin at an extinct
volcano, then meander and
sometimes split as they are
followed across the
surface.
• Pictures from Apollo 15 at
the edge of the Hadley
Rill.
Apollo to the Moon
• First, I believe that this nation
should commit itself to
achieving the goal, before this • We choose to go to the moon.
decade is out, of landing a man We choose to go to the moon in
on the moon and returning him this decade and do the other
safely to the earth. No single things, not because they are
space project in this period will easy, but because they are hard,
be more impressive to mankind, because that goal will serve to
or more important for the long- organize and measure the best
range exploration of space; and of our energies and skills,
none will be so difficult or because that challenge is one
expensive to accomplish. John that we are willing to accept,
F. Kennedy 1961 one we are unwilling to
postpone, and one which we
intend to win, and the others,
too.
• John F. Kennedy 1961
Moon Exploration
• The Apollo missions
explored the moon from
1968 to 1972.
• Six missions successfully
landed on the moon.
• Apollo 11 was the first in
July 1969.
• Apollo 17 was the last, in
December 1972. We have
not gone back since.
Apollo 11
• First lunar landing: July
20, 1969.
• Neil Armstrong and Buzz
Aldrin took the Lunar
Module Eagle down to the
surface of the moon.
Michael Collins remained
in orbit in the Command
Module.
• “That’s one small step for
man, one giant leap for
mankind.”
Apollo Contributions
• Returned 382-kg of rocks.
• Genesis rock showed that
the moon was almost as
old as the Earth (4by).
• Spinoffs include cordless
tools, computers,
CAT/MRI technologies,
kidney dialysis machines,
freeze dried food, and
countless others have
benefited mankind.