Sun & moon cycles (big teach)

Cycles related to the
movement of objects in
the Solar System

By Moira Whitehouse PhD

On Earth we notice some cycles that occur
at regular intervals.

Some of these cycles are day and
night, years, seasons, moon phases
and tides.

These cycles are determined by how the
Earth, the Sun and the Moon move relative
to one another in space.

The Earth moves around (orbits) the Sun.
At the same time as the Earth is revolving
around the Sun, the Moon moves around
(orbits) the Earth.

As the Earth and Moon are orbiting, they are also
spinning around (rotating) on an imaginary axis.

Earth rotating.

These movements result in the cycles of day and
night, years, seasons, moon phases and tides.

Cycles (Effect) Cause(s)

Day and night Earth rotating
one rotation=one day or 24 hours

Years Earth revolving or orbiting the Sun
One revolution or one orbit = one year

Seasons Earth’s axis on a tilt and
Earth orbiting the Sun
One revolution= 4 seasons
summer, fall, winter, spring

Moon phases Moon orbiting the Earth
One revolution=8 moon phases

Tides Moon’s gravity pulling on the Earth’s oceans
Two high tides and two low tides every day

Why do we have day and night?

We have day because there is sun light on
our side of the planet.

We have night because there is no sun
light on our side of the planet.

Sunlight Sunlight

Day time

Night time http://starchild.gsfc.nasa.gov

The side of the Earth facing the Sun
experiences day time.
The side of the Earth facing away from the
Sun experiences night time.

As the Earth circles the sun it also rotates
on it axis (an imaginary line passing
through the North and South poles).

As it rotates only
half of the Earth at
a time is in the sun
light. In that half it
is day time.
The other half is in
shadow, the sun is
not visible and it is
dark. In that half it is
night time.
The Earth’s rotation
causes every part of
http://sos.noaa.gov/
the earth to have both
day and night time.

Our clocks and calendars are based on one
day being 24 hours long. As can be seen by
this diagram,
that’s about
how it takes for
the Earth to
make one
rotation on its
axis.

Sunrise
coming
to the
Horn of
Africa

Cycles Cause(s)



Seasons Earth’s axis on a tilt and



How is our year based on the relationship
between Earth and Sun?

Years: Earth revolving or orbiting the Sun

While rotating on its axis every day, the
Earth is also making a very long trip
revolving around (or orbiting) the Sun.

The amount of time it takes for the Earth
to make one complete revolution around
the Sun is one year or 365 ¼ days.
Every four years we have leap year in
which we add one day to the calendar
to make up for the four one-fourth days.

One trip (oribt) around the Sun (point A back to point A)
takes Earth one year of travel time. That is how people
came up with the idea to measure time in years.

A

Why is the weather different at different times
of the year? Why do we have seasons?

Seasons: Earth’s axis on a tilt and

We will look at the two reasons for seasons:

1. The Earth orbiting the Sun
Without this there would be no seasons,
but there would also be nothing else.

2. The tilt of the Earth on its axis as it orbits
the Sun
Is the reason we have seasons, as we will
see.

If the Earth’s axis were
straight up and down as
shown in this picture,
there would be no
seasons. Weather, yes,
but no seasonal patterns.

But it is not, it is tilted as
shown in this picture.
And now we shall see
how that causes the
seasons.

Just how much
is the Earth
tilted?

The axis of the
Earth is tilted
23.5 degrees.

Wikipedia Commons

23.5º

The northern axis of the
Earth happens to point
within one degree to
Polaris, a fairly bright star
North we call the North Star.
Star

Because of the tilt of the earth, during certain
positions in its orbit of the Sun the Earth’s Northern
Hemisphere is tilted toward the sun; and six months
later and on the opposite side of the orbit, the
Southern Hemisphere is tilted toward the sun.

Southern
Hemisphere tilted
towards the Sun

Northern
Hemisphere tilted
towards the Sun

Spring

Or, from another view point

Summer Summer
Summer
Winter

Summer

http://www.seed.slb.com/ Permission is granted to make copies of this document for educational purposes only.
Fall


We can see that in the warmer “summer”
months, the Earth is not closer to the sun
as people often think.
It is actually how direct the sun’s rays
strike the Earth that determines seasonal
temperatures.
A given amount of heat energy must cover a
greater amount of space (and is therefore
weaker) the further it is from the equator
when it strikes the earth.

As seen here, the sun’s incoming energy (we will call it four
units) is more concentrated and covers a smaller circle nearer
the equator than the same four units covering a much larger
circle closer to the poles.

Lower latitudes near the earth’s equator, therefore, receive a
greater concentration of incoming energy and are warmer
than higher latitudes.

This animated visual shows the Earth
moving in orbit through the seasons.

http://esminfo.prenhall.com/science/geoanimations/animations/01_EarthSun
_E2.html

Another animation showing the Earth
moving in orbit through the seasons.
Look through the list and choose
“Seasons Interactive”.

http://highered.mcgraw-
hill.com/sites/0072482621/student_view0/int
eractives.html#

Fall in the Spring in the
Northern Southern
Hemisphere Hemisphere
Winter in the
Northern
Summer in the
Hemisphere
Northern
Hemisphere

Winter in the
Summer in Southern
the Southern Hemisphere
Hemisphere
Spring in the Fall in the
Northern Southern
Hemisphere Hemisphere
http://www.srh.noaa.govhttp://www.srh.noaa.gov

An animation showing the day and
night, years and seasons. Under
“Earth and Beyond” choose “The
Earth”.
http://www.engineeringinteract.org/resources
.htm

What causes the Moon's phases?
The Moon goes through these phases
because: 1) the Moon is revolving around the
Earth, and 2) the Moon is reflecting sunlight
towards the Earth.

Half of the Moon is always lit, not just the
portion we see: however, sometimes we
only see the lit portion of the Moon based
on where it is in its orbit.

Before an in-depth study of the Moon’s phases, we
will look at the Moon’s relationship with the Earth.

The moon
rotates on
its axis as it
orbits the
Earth.

NASA

At the same time as the Earth is rotating
and orbiting (revolving around) the Sun,
the Moon is rotating and orbiting the Earth.

Earth’s axis

Moon orbits
the Earth
Earth orbits
the Sun

Now to that “in-depth” look at the phases
of the Moon.

There are eight phases that the moon
goes through and they always occur in
the same order.

The Sun's light seems to move from right
to left across the surface of the Moon.

The phases of the Moon are:
1) New Moon,
2) Waxing Crescent
3) First Quarter,
4) Waxing Gibbous
5) Full Moon,
6) Waning Gibbous
7) Last Quarter
8) Waning Crescent

And back to the New Moon.

New Waxing First
Moon Crescent Quarter

Waxing Full Waning
Gibbous Moon Gibbous

Third Waning New
Quarter Crescent Moon

Let’s look at the phases of the moon on a
calendar for November, 2009. Notice that
the change from phase to phase is very
gradual and takes about a month for the
cycle.
http://www.tutiempo.net/en/moon/

Select Moon Phases in the following URL
for an outstanding animation of the Moon
and its phases.

http://www.valdosta.edu/~cbarnbau/astro_de
mos/frameset_moon.html

As shown in the diagram, the new moon
occurs when the moon is positioned
between the earth and sun. The entire
illuminated
(lit up) side of
the moon is on
the back part
of the
moon–
the half that
we cannot see.
http://www.wiseg
orilla.com

At a full moon, the earth, moon, and sun are
in approximately lined up, just as the new
moon, but this time the moon is on the
opposite side of the
earth. As a result,
the entire sunlit
part of the moon
is facing us. The
shadowed portion
is entirely hidden
from view.
http://www.wise
gorilla.com

The first quarter and third quarter moons
(both often called a "half moon"), occur when
the moon is at a 90 degree angle with respect
to the Earth
and Sun. So we are
seeing exactly half
of the Moon
illuminated and
half in shadow.

http://www.wise
gorilla.com

It takes for the Moon 29.5 days to
orbit the Earth, about one month.
(Also the amount of time from one
new moon to the next).

What causes tides in the ocean?

The Moon’s gravity pulling on the
Earth causes the tides.

To understand Moon tides we must have
some idea about gravity.
Gravity is a force.
Gravity is a force that pulls.
Every object has gravity.
So every object pulls on every other
object.
The more mass an object has, the harder
it pulls.

We will use two hypothetical planets for our
example. Both the blue and green planets
are pulling on each other.

Which one pulls harder?

This should help us see that the more mass
an object has the stronger its gravity.

Moon Earth

The Earth obviously has more mass than
But the Moon’s gravity is also pulling on
the Moon and it pulls harder.
the Earth. So hard that the oceans swell
So much harder that theever it passes. in an
toward the Moon where Moon is held We
call this high tide. Earth as though by some
orbit around the
magically strong string.

Hopewell rocks at at low and high tides.

Ocean tides are
caused by the
gravity of the
moon pulling on
the ocean’s water.
As a result of this
pull of gravity, the
ocean’s water bulges toward the Moon on
every rotation of the Earth. This bulge is
called high tide and it occurs about every 12
hours—twice a day. Low tide occurs
between high tides.

The point is, because of the Moon’s gravity,
the ocean’s water bulges toward the Moon on
every rotation of the Earth.

Would the tides be greater if the Sun and
Moon were lined up? Why?

Sun

Open this website and choose tides.
All good, but these two
especially important for
understanding tides.

http://www.valdosta.edu/~cbarnbau/astro_demos/frameset_moon.html`

Cycles Cause(s)



Seasons
In Review...

Earth’s axis on a tilt and



Sun & moon cycles (big teach)

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