The Moon & Tides

Chapters

22.2 & 16.2

Motions of the Earth-Moon System

• Orbital period = about one month

• The moon’s orbit is elliptical

• It is tilted 5 degrees off of Earth’s orbital plane

Perigee: Moon is closest to Earth Apogee: Moon is farthest from Earth

Average distance from Earth to the moon = 384,000 km = 238,607 miles!

Phases of the Moon

• phases: various shapes of the moon lighted by reflected sunlight

Brain Pop:

Moon Phases

• waxing: when the size of the visible portion of the moon is increasing

• waning: when the size of the visible portion of the moon is decreasing

• new moon: no lighted area of the moon is visible from the Earth

•full moon: entire half of the side of the moon facing Earth is lit

• crescent: less than half of the side facing the Earth is lit

•gibbous: more than half of the side facing the Earth is lit

Waxing crescent

1st quarter

New moon

Waxing gibbous

Full moon Waning gibbous

3rd quarter Waning crescent

Lunar Motions • Synodic Month: The cycling of the moon through its phases (Apparent Motion)

• 29 1/2 days • Basis for the first Roman calendar

• Siderial Month: The moon revolutionary period around the earth (Actual Motion)

• 27 1/3 days

•Occurs because Earth is revolving around the sun at the same time as the moon is revolving around The Earth!

• Why does the same side of the moon always face us?

• Because the moon rotates and revolves at the same speed:

27 1/3 days!

Eclipses

• when one planetary body passes through the shadow of another

Brain Pop:

Eclipse

• solar eclipse: when the moon is directly between the Earth and the sun

• lunar eclipse: when the Earth is directly between the moon and the sun

• Eclipses don’t occur every month because the moons orbit is tilted with respect to the Earth’s orbit

Tides Daily changes in the elevation of the ocean surface

Result from gravitational attraction between… Earth, Moon, & Sun

Brain Pop:

Tides

The earth has a uniform level of water all around it.

2 forces act on the water to produce tides…

The moon’s GRAVITY pulls on the earth, and the water bulges toward the moon.

Because the earth is spinning, there is a force pulling water in the opposite direction INERTIA

As the earth turns upon its own axis in about 24 hours, a point on the earth moves through areas with these different forces acting on it.

The Result…

Spring Tide – tides have

greatest tidal range because the gravity of the sun & moon are combined

Neap Tide – daily tidal

range is lower than average because the

gravity of the sun & moon counteract each other

Tidal Patterns

Diurnal - One high tide & one low tide each day

Semidiurnal - Two high tides & Two low tides each day

Tidal Graphing

One Day

Multiple Days