Download Sponge: What two factors cause the seasons on Earth?

Sponge:
What two
factors cause
the seasons
on Earth?
The constellations
change with the
seasons because
the night side of Earth
faces a different set
at different times
of the year.
The time required for
the constellations to
complete one cycle
around the sky is called
a sidereal year and is
365.256 solar days long.
The twelve
constellations
the Sun passes
through is called
the zodiac.
The moon
goes through a
repeating set
of phases.
Phases of the moon:
• New – none of the visible surface of the moon is
illuminated.
• Crescent – less than half of the visible surface is
illuminated.
• Quarter - half of the visible surface is illuminated.
• Gibbous - less than half of the visible surface is
illuminated.
• Full - all of the visible surface of the moon is
illuminated.
The moon cycle begins
when the moon is new,
none of the visible surface
is illuminated. Then the
moon waxes (grows),
first being a crescent
moon.
The illuminated visible
surface continues to wax
until half of the visible
surface is illuminated.
This is the first quarter.
(It is called a quarter moon
because we see ¼ of the total
surface of the moon illuminated.)
The moon continues to
wax (grow) beyond the
quarter moon so more
than half of the visible
surface is illuminated.
This is a gibbous moon.
The gibbous moon
continues to wax until
the entire visible
surface is illuminated.
This is a full moon.
At this point, the visible
illuminated surface begins
to shrink. This is called
waning and produces a
gibbous moon. This is
called a waning gibbous.
The gibbous moon
continues to wane until it
forms the last quarter. It
then becomes a waning
crescent and continues to
wane until it returns to the
new moon phase.
Sidereal month (27.3 days) moon
returns to the same
position on the
celestial sphere.
Synodic month (29.5 days) moon
returns to the same
phase. The synodic
month is longer
because Earth moves
around the Sun.
Eclipses occur when the
moon blocks the sun
during the day and the
moon’s shadow crosses
over the earth or when the
shadow of the earth
crosses over the moon.
A lunar eclipse occurs
when the Sun and
Moon on opposite sides
of the Earth.
The Earth’s shadow
falls on the Moon.
A lunar eclipse may
be partial or total.
Lunar eclipses last
for approximately
100 minutes.
During a lunar eclipse the
moon is a reddish color
because some sunlight is
bent by the Earth’s
atmosphere and reaches the
Moon. This light is reddish for
the same reason that the
sunset is red and orange.
A solar eclipse
occurs when the
Sun and Moon
are in the same
direction relative
to the Earth.
In a solar eclipse
the moon’s
shadow falls
on the earth.
The umbra is a part of this
shadow on the earth. It is
the area of totality, where
all of the light from the
sun is blocked. This
total eclipse lasts for
7.5 minutes.
The rest of the shadow is
called the penumbra. The
penumbra is the area of
partial eclipse. It is the
area where not all of the
light form the sun is
blocked by the moon.
An annular eclipse is
an eclipse where the
umbra never reaches
Earth. The sun appears
as a ring around the
moon in its new moon
phase.
The fact that there are
annular eclipses shows that
the distance of the Moon
from the Earth is not
constant. The moon gets
farther away from and
closer to the earth over
the course of its orbit.
The moon’s orbit is
inclined to the
ecliptic, or there
would be eclipses
every month.
The line of nodes is where
the orbits of the sun and
moon cross and thus
marks the favorable
seasons for eclipses.
These eclipse seasons
occur twice each year.
The Sun’s gravitational pull
on the Moon “messes” with
the Moon’s orbital orientation.
This makes the moon’s orbit
“wobble” so the nodes, the
points where the moon’s orbit
and the earth’s orbit cross,
move over time.
This causes
the regression
of nodes.
This causes the regression of nodes.
It is a remarkable
coincidence that the Sun
and Moon occupy the same
size on the celestial sphere,
1/2 of one degree. If this
were not so, we would not
see these eclipses.
The Earth’s axial tilt
varies between 22
and 24 ° because of
the gravitational pull
of the Moon and
Jupiter.
This also causes
the Earth’s axis to
change direction over
time. This is called
precession.
As a result of this “wobble’
of the axis, the vernal
equinox drifts slowly
around the zodiac.
Despite the song, we are
actually not in the “Age of
Aquarius” just yet.
This will also cause the
north star to change.
Today it is Polaris. In
3000 B.C., it was
Thubin. In 14000 A.D.,
it will be Vega.