8-4.4 Days, Years, Moon Phases, Eclipses and Tides
8-4.4
Days, Years, Moon Phases,
Eclipses and Tides
Day • A day is based on the 24 hours it takes
Earth to rotate.
• Earth rotates on its axis counterclockwise
from west to east; as a result, the Sun
appears to rise in the east and set in the
west.
Year
• A year is based on the 365.25 days it
takes Earth to revolve around the Sun.
• Earth revolves around the Sun in an
elliptical orbit.
Lunar Movement
• The Moon revolves with the Earth around the Sun as the Moon
is revolving around the Earth.
• The Moon revolves around Earth in 29.5 days.
• Similarly to Earth, as the Moon revolves, it is rotating or
spinning on its axis.
• The rotation time for the Moon is a little over 27 Earth days.
• Because the Moon rotates and revolves in nearly the same
amount of time, the same side of the Moon always faces Earth.
Phases of the Moon
• The Moon’s “phase” is the amount
of the lit side of the Moon we can
see.
• The phase depends on the relative
positions of the Sun, the Earth,
and of course, the Moon.
The Moon is Earth’s
Satellite
• Remember, just as Earth revolves
around the Sun, the Moon
revolves around the Earth. This is
important because it causes
shadows to be cast between the
Earth and Moon.
The New Moon
• The Moon is directly between the Sun
and the Earth.
• The Sun is lighting up the “dark side”
of the moon (the side we never see).
• The Moon is high in the sky, but can’t
be seen.
Waxing Phases
• As the Moon’s revolution continues, we start
to see a sliver that is illuminated by the Sun.
• The Waxing Phases are:
–Waxing Crescent (just a sliver)
–1st Quarter (half of the side that faces us is
lit)
–Waxing Gibbous (approaching full)
Tidbit: “gibbous” is Latin for “humpbacked”
The Full Moon
• The Full Moon only occurs when the
Moon is on the opposite side of Earth &
we can see the Sun fully illuminating it.
• P.S. We can only see ½ the Moon, so
could you call it a 2nd Quarter Moon
seeing how we have a 1st Quarter & 3rd
Quarter phase?
The Waning Phases
• After the Moon is full, the amount of what
we can see begins to recede (go away).
• The Waning Phases are:
–Waning Gibbous
–3rd Quarter (opposite than the 1st Q)
–Waning Crescent
…and then it starts all over again!
Eclipses
• An eclipse is a result of an alignment of Earth,
Sun, and Moon when either Earth or the Moon
temporarily blocks the Sun’s light from reaching
the other.
• Sometimes, during a New Moon, the Moon’s
shadow falls on Earth & causes a Solar Eclipse.
• Other times, during a Full Moon, the Earth’s
shadow falls on the Moon and causes a Lunar
Eclipse.
Lunar Eclipses
• Earth is directly between the Sun & the Moon.
• Lunar eclipses ONLY happen during a FULL MOON.
Solar Eclipses
• The Moon is directly between Sun and Earth.
• Solar Eclipses ONLY happen during a NEW MOON.
Tides • Tides are changes in the surface levels of
Earth’s ocean water. • Tides are caused by the effects of the Moon’s
and Sun’s gravitational pull on Earth.
Types of Tides •High Tides •Low Tides •Spring Tides •Neap Tides
High Tides •As moon orbits Earth, the waters of Earth closest to Moon bulge outward toward the Moon. Another bulge forms on the opposite side of Earth. These bulges are high tides.
High Tides
Low Tides •While most of Earth’s water is pulled toward the high tide bulges, the areas between high tides are called low tides.
Low Tides
Extreme Tides: Spring Tides • When Sun, Earth, and Moon are aligned in a straight
line, during New & Full phases, high tides are much higher than normal and low tides are much lower than normal. The tidal range is greater than normal.
•Straight=Spring
Spring Tides
Extreme Tides: Neap Tides • When Sun, Earth, and Moon are aligned at a 90 degree
angle, during 1st & 3rd Quarter phases, high tides are lower than normal and low tides are higher than normal. The tidal range is less than normal.
•Ninety=Neap
Neap Tides