Download The Sun-Earth

27.3
The Sun-Earth-Moon System
Daily Motions
• The moon rises in the east and sets in the west
• These daily motions result from the Earth’s rotation
• The sun, moon, planets, and stars do not orbit around the
Earth every day
• It appears that way because we observe the sky from a planet
that rotates
Earth’s rotation
• We have to look at the Earth’s rotation first before we can
understand the moon’s daily motions
• The time period from one noon to the next is called a SOLAR
DAY
• Our timekeeping system is based on a solar day
• The Earth requires 4 more minutes each day so it can turn a
little farther each day to align with the sun
• This is because the Earth and spinning and orbiting
Annual Motions
• Earth orbits the Sun in a slightly
elliptical orbit.
• This plan of Earth’s orbit is
called the ECLIPTIC PLANE
• As the Earth rotates, the sun,
planets, and constellations
appear to move across the sky
in a path known as the
ECLIPTIC
• As Earth moves in orbit,
different constellations are
visible
The Effects of Earth’s Tilt
• Earth’s axis is tilted relative to the ecliptic at approximately
23.5°
• As Earth orbits the Sun, the orientation of Earth’s axis remains
fixed in space so that, the northern hemisphere of Earth is
tilted towards the Sun
• After six months, the northern hemisphere is tipped away
from the sun
• What is the result of this?
• Seasons!
Solstices
• At a given solstice, the Sun is overhead at its farthest distance
either north or south of the equator
• There are 4 positions (1, 2, 3, 4)
• Position 1 corresponds to the summer solstice in the northern
hemisphere when the sun is directly overhead at the Tropic of
Cancer
• At this time, June 21st, the number of daylight reaches its
maximum
• The sun is up all day within the Artic Circle
Solstices
• On this day, the number of daylight house in the southern
hemisphere is at its minimum, and the sun does not appear in
the region within the Antarctic Circle
• Solstices explained
Solstices
• As Earth moves past position
2, the suns altitude decreases
in the northern hemisphere
until earth reaches Position 3,
known at the WINTER
SOLSTICE
• This happens around
December 21st
• The earth continues around
its orbit past Position 4 and
onto Position 1
Equinoxes
• An equinox are found in position 2 and 4, where the Earth’s
axis is perpendicular with the Sun’s rays
• The term equinox means ‘equal nights’
Phases of the Moon
• Just as the sun appears to
change position in the sky
throughout the year, the
moon also changes position
relative to the ecliptic plane
as it orbits Earth
• The Moon’s cycle is more
complex!
• The moon’s cycles are called
lunar phases
Waxing and Waning
• Starting at the new moon, as you increase the sunlit side of
the moon, it is known as the WAXING PHASE
• The waxing phases are called
• Waxing crescent
• First Quarter
• Waxing Gibbous
Waxing and Waning
• Once you have a full moon, the entire sunlit side of the moon
faces the Earth
• After this, the moon begins to decrease the amount of sunlit
side, known as the WANING PHASE
• Waning Gibbous
• Third Quarter
• Waning Crescent
Explained Video
Synchronous Rotation
• The surface features of
the moon always look the
same
• As the moon orbits Earth,
the same sides faces
Earth at all times
• The Moon spins exactly
once each time it goes
around the Earth
• Explained
Lunar Motions
• The length of time it takes for the Moon to go through a
complete cycle of phases, is called a LUNAR MONTH
• The lunar month is about 29.5 days
• The moon rises and sets 50 minutes later each day
Tides
• One effect the Moon
has on Earth is causing
ocean tides
• The moons gravity pulls
on Earth along an
imaginary line
connecting the Earth
and the Moon
• Spring Tides = High
• Neap tides = Low
• Tides Explained
Solar Eclipses
• Occur when the Moon passes directly between the Sun and
the Earth and blocks the sun from view
• You can have complete solar eclipses and partial solar eclipses
• Explained
Annular Eclipses
• Occurs when the Moon is too far away for its umbral shadow
to reach Earth
• A ring or annulus, is left uncovered
Lunar Eclipses
• Occurs when the Moon passes through Earth’s shadow
• A total lunar eclipse occurs when the entire moon is within
the Earth’s umbra.
• Lasts usually 2 hours
• Explained