Tides and Eclipses

• Read Your Textbook: – Chapter 3

• Homework Problems– Review Questions: 1, 2, 5, 8– Review Problems: 1, 2, 6– Web Inquiries: 3, 4 (1, 2 in 5th ed.)

Earth and Moon• The Moon is …

– 1/4 the diameter of the Earth– 1/100 the mass of the Earth– 1/50 the volume of the Earth– 60 Earth radii away– Gravitationally locked in a synchronous orbit (the far

side is never seen from the earth)

• To Scale...

Earth Moon

Same Side View

• The moon’s rotation equals its revolution period.

• The same side always faces earth.

• 50% is always illuminated by the sun.

Observational Apparitions

Moon Horizon Illusion

http://www.GriffithObs.org/IPSMoonIllus.html

Observational Apparitions

Man on the Moon?

Observational Apparitions

Lady on the Moon?

Observational Apparitions

Lady on the Moon?

Observational Apparitions

Toad on the Moon?

Observational Apparitions

Toad on the Moon?

Observational Apparitions

Tidal Forces

• As the Earth Rotates, we are carried into and out

2 High and

2 Low Tides

Every Day

Tides (Weak and Strong)

• Sun’s tidal influence is ~ 1/2 that of the moon

Strongest Tides

Moon New or Full

Weakest Tides

Moon 1st or 3rd quarter

Other Factors

• Winds

• Ocean Currents

• Coast Line Geometry and Topography

• Tides are predictable for any given location!

Moon’s Orbit• Sidereal Month

– Orbit– Star reference

• Synodic Month– Phases– Sun reference

Observing From Spaceship Earth

horizon

Spaceship Earth

horizon

Spaceship Earth

horizon

Spaceship Earth

horiz

on

Spaceship Earth

hori

zon

Earth Rotation

Stars settingStars rising

Stars overhead

Lunar Phases

Lunar

location

with respect

to the sun

determines

phase seen

at the earth.

Lunar Phases

• The 3rd quarter moon rises when?

• The full moon sets when?

Lunar Phases

• New 0.00

• 1st Quarter 0.25

• Full 0.50

• 3rd Quarter 0.75

horizon

Lunar Phases

• The 3rd quarter moon rises when?– Rises at Midnight– Sets at Noon

• The full moon sets when?– Sets at Sunrise (6 am)– Rises at Sunset (6 pm)

Observational Geometry

horizon

Observational Geometry• Inner Planets

– Mercury

– Venus

• Outer Planets– Mars

– Jupiter

– Saturn

– Uranus

– Neptune

– Pluto

Sun

Earth Orbit

Inner Planet

Outer Planet

Conjunctions

• Inner Planets– Conjunction (Aligned with the Sun)

• Inferior

Sun

Conjunction

• Outer Planets– Conjunction (Aligned with the Sun)

• Always Superior, Never Inferior

Sun

Conjunctions

• Inner Planets– Conjunction (Aligned with the Sun)

• Inferior

• Superior

Sun

Elongation

• Inner Planets– Conjunction (Aligned with the Sun)

• Inferior

• Superior

– Greatest Elongation

(Farthest From Sun)• Eastern

• Western

Sun

Elongation

• Inner Planets– Conjunction (Aligned with the Sun)

• Inferior

• Superior

– Greatest Elongation

(Farthest From Sun)• Eastern

• Western

Best Time to View

Inner Planet

Conjunction

• Outer Planets– Conjunction

• Aligned with the Sun

• Always Superior, Never Inferior

Sun

Opposition

• Outer Planets– Conjunction

• Aligned with the Sun

• Always Superior, Never Inferior

– Opposition• Opposite the Sun

• Earth Closest Approach

Best Time to View

Outer Planet

Sun

Eclipse Conditions

New or Full Moon

Moon at a

“NODE”

in its orbit.

Lunar Eclipse• Moon in Earth’s Shadow

Eclipses Are Shadows• Solar Eclipse Shadow Caught By Weather Satellite Image

Solar Eclipse Geometry

Total Solar Eclipse

Partial Solar Eclipse

Annular Solar Eclipse

The Saros Cycle

The repeating of eclipse geometries known to the ancients:

http://sunearth.gsfc.nasa.gov/eclipse/SEsaros/SEsaros.html

The Eclipse Home Page:

http://sunearth.gsfc.nasa.gov/eclipse/eclipse.html