chapter 2 (2.3): the earth/moon/sun topics 1. moon phases 2. eclipses: shadows and visualizing the...

Chapter 2 (2.3): The Earth/Moon/Sun

Topics 1. Moon phases

2. Eclipses: shadows and visualizing the earth/moon/sun

3. Solar calendars vs Lunar calendars.

4. Distances and angles

* Visualize in 3D!

* Ask “How do we know?”

• What determines the appearance of the moon? – What is moonlight?

– Why does the moon rise in the east, set in the west?

– Why does the moon’s appearance change?

1- Moon phases

• What determines the appearance of the moon? – What is moonlight? Reflected sunlight!

– Why does the moon rise in the east, set in the west?


1- Moon phases


– Why does the moon rise in the east, set in the west? The earth spins!


1- Moon phases


– Why does the moon rise in the east, set in the west? The earth spins!

– Why does the moon’s appearance change? Because it ORBITS the EARTH!

1- Moon phases

1. The earth orbits around the Sun and spins on its own axis in the same sense (i.e. both clockwise or both anticlockwise)

2. A siderial day is defined as the time it takes the Earth to make a complete spin on its axis relative to distant stars

3. A solar day is defined as the time it takes the Earth to do a complete spin on its axis relative to the Sun

1. The length of a siderial day is about 4 minutes shorter than the length of a solar day

Background for i>clicker Quizzes: Siderial vs Solar Time

1- Moon phases

phases:

new

waxing crescent

first quarter

waxing gibbous

full

waning gibbous

third quarter

waning crescent

new

1- Moon phases

When does a FULL MOON rise?

When does a NEW MOON rise?

Does an astronomer on the moon see the Earth “rise” or “set”?

Does he/she see phases of the Earth?

1- Moon phases

1- Moon phasesWhen does a FIRST quarter MOON rise?When does a NEW MOON rise?

For the picture at right, what is the phase of the Moon as seen from Earth?

When does a FIRST quarter MOON rise?When does a NEW MOON rise?

For the picture at right, what is the phase of the Moon as seen from Earth?

1- Moon phases

When does a FIRST quarter MOON rise?When does a NEW MOON rise?

For the picture at right, what is the phase of the Moon as seen from Earth? Crescent

1- Moon phases

The Earth/Moon/Sun

Topics 1. Eclipses: shadows and visualizing the earth/moon/sun

* Visualize in 3D!

2- Eclipses • Lunar eclipse = Earth casts shadow on Moon (E between M & S)

• Solar eclipse = Moon casts shadow on Earth (M between E & S) NOTE! Earth, moon, and sun are rarely perfectly aligned!

2- Eclipses – Lunar

Partial vs Full shadows … the sun is not a dot!

• Full = Umbra

• Partial = Penumbra

(our vantage point for

these drawings is looking

DOWN on the last slide.)

Total Lunar Eclipse, Jan 9/10, 2001


• Blue light is scattered more efficiently Earth’s atmosphere

(Daytime sky looks blue.)• Red light is scattered less efficiently (setting sun looks red)

And the path of light (all colors) is bent by mass (general relativity!)

• Why does the moon appear red during a full lunar eclipse?


• The Sun and moon are coincidentally same angular size when seen from Earth.

2- Eclipses – Solar

• The Sun and moon are coincidentally roughly the same angular size when seen from Earth.

Why are Solar Eclipses so much rarer than Lunar eclipses?


As day progresses, moon moves in between earth and sun..2- Eclipses – Solar

As day progresses, moon moves in between earth and sun..Practice questions

During a solar eclipse:

A- The Earth’s shadow falls on the Sun

B- The Moon’s shadow falls on the Earth

C- The Sun’s shadow falls on the Moon

D- The Earth’s shadow falls on the Moon

E- The Earth stops turning

F- The moon falls out of the sky.

G- Birds fall from the sky

H- The Sun falls from the sky.

As day progresses, moon moves in between earth and sun..Practice questions

(You can’t cast a shadow onto the light source.)

Moon does cast a shadow on Earth.

(The light source can’t cast a shadow of itself.)

Earth casts a shadow on the Moon during a LUNAR eclipse.

(I really hope not. What would stop it? What would restart it?)

(I really hope not…)

(Better get indoors!)

(Better find another planet to live on.)

During a solar eclipse:

A- The Earth’s shadow falls on the Sun

B- The Moon’s shadow falls on the Earth

C- The Sun’s shadow falls on the Moon

D- The Earth’s shadow falls on the Moon

E- The Earth stops turning

F- The moon falls out of the sky.

G- Birds fall from the sky

H- The Sun falls from the sky.

Photo of eclipse from orbit


Solving the Mystery of Planetary Motion (use of the Scientific Method)

* Visualize in 3D! * Ask “How do we know?”

1. Observe / Question2. Hypothesize / Explain3. Predict4. Test!

A heliocentric model where planets move on ellipses = excellent predictions

5.8_Planetary Orbit Simulator --Kepler's laws

Kepler’s Three Laws of Planetary Motion

Kepler’s 1st Law:

All planets have elliptical orbits w/ the sun at one focus.

(Eccentricity of Earth’s path = 1.7%… nearly perfect circle.)


Brief aside about ellipses:

The ellipse is completely defined by: center, the eccentricity, and the length of the semi-major axis

The focii are just geometrically defined points.The sun lies at one focus of elliptical orbit of each planet.

Brief aside about ellipses:

An ellipse is defined by: center, the eccentricity, and the length of the semi-major axis

If eccentricity is 0… then the foci are at the center, and it’s a circle.

Keplers 2nd Law:

A planets sweeps out equal areas in equal times

(i.e. Moves fastest at perihelion and slowest at aphelion.)

5.8 Planetary orbit simulator kepler's 2nd law


Kepler’s 3rd Law:

The ratio of

(a planet’s average distance from the Sun)3 to (its orbital period)2

is a constant for all the planets.

distance3 = distance * distance * distance

(time to orbit)2 = (time to orbit) * (time to orbit)


A planet that is close to the Sun, completes an orbit in a shorter period of time than a planet that is farther from the Sun.

Light and EnergyTopics

1. How light (=energy) and matter interact

How light (= energy) and matter interact

A. What is the structure of matter?

B. How is energy stored in atoms?

C. What is light?



Atoms = Nucleus + Electron cloud

Nucleus contains protons (p) and neutrons(n)Electrons (e) sort of “orbit” the nucleus





• these particles have “charge”

electrons ….. -1 e- (defines a fundamental unit of charge)protons ……. +1 e-

neutrons ………0 (neutral)

• a neutral atom has net charge = 0 (#p’s = #e’s)





q= charger = distance between

• like charges repel each other, opposite charges attract

• atoms will attract electrons until net charge = 0 (#p’s = #e’s) !

€

FEM =Kq1q2

r2

You won’t need to use this formula.Just notice the similarity to gravitational Force.

• Atomic Number = # of protons in nucleus

• Atomic Mass Number = # of protons + neutrons

• Molecules: consist of two or more atoms (H2O, CO2)



• Isotope: same # of protons but different # of neutrons. (4He, 3He)



Ground State

Excited Electron States

If there is a FORCE (gravitational or electromagnetic) , there can be

STORED ENERGY.

STORE energy = go to high potential energy.RELEASE energy = “fall” back down

Key point:

The states available to electrons in atoms are

QUANTIZED

Electrons in an ATOM can only have “sit” at specific energy levels,

which are determined by the #n’s and #p’s in the nucleus..




Energy level transitions:

The only allowed changes in energy

for an electron while it is still trapped in the atom are those corresponding to a transition between energy levels

AllowedNot Allowed




Light = energy (sunlight feels warm!)

Energy unit: Joule Flow of energy: Watt = 1 Joule / second

The flow of energy is the rate that energy is… moving… delivered to earth

example: rate that energy is used in a lightbulb rate that energy (aka photons aka sunlight)

hits the earth from the sun




C. What is light?

Light = energy (sunlight feels warm. The light that hits your skin delivers energy!)

You can think of light as WAVE or as a PARTICLE : “wave/particle duality”

a particle (i.e. a photon) --- because it acts like a “packet” of energy.

a wave --- because it moves like a wave moves (mathematically convenient)




C. What is light: photons or waves?

“wave/particle duality”





• A wave is a pattern of motion that can carry energy without carrying matter along with it

• Wavelength = λ distance between two wave peaks

• Frequency = f

number of times per second that a wave vibrates up and down

• Speed of light = ALWAYS the SAME

wave speed = wavelength x frequency

wave speed = λ * f





A particle of light, a photon, is like an energy packet.

The energy carried by the photon is related to its wavelength and frequency.

photon’s energy:

Energy = [Constant] * frequency ……………goes UP if frequency goes up!

Energy = [another constant] * 1/ wavelength … goes DOWN if wavelength goes up (longer distance between peaks)





Prisms bend the path of photons according to their energy.

White light contains a continuum of energies (wavelengths).

Our eyes are photon detectors!

Different energy photons are perceived as different COLORS





Electromagnetic Spectrum:

high energy(break down molecules, damage DNA, release e- in metals)

Moderate energies (“visible” bandpass, aka “optical” bandpass)(the amounts of energy that release electrons from atoms)

low energy(Can “shake” e-’s in metals, causing current in antennae, receivers, etc) (“radio waves” are are photons, NOT sound!)

f unit: hertz = #/sec = s-1

E=hf unit: eV (= 1.6e-19 J) or Joules

• From atoms -- electrons release photons with only certain energies– Each chemical (# p’s) has a unique set of energy levels that its

electrons can occupy. (quantized energy levels!)– Electrons can move between levels:

2- Line emission

Get energy = absorb a photon, move to a higher level

Lose energy = emit a photon, fall to a lower energy level

• From atoms -- electrons release photons with only certain energies– Each chemical (specific # of p’s) has a unique set of energy levels

that electrons in its atoms can occupy (quantized energy levels!)– Electrons can move between levels– Each chemical element has its own “fingerprint” of energy levels

2- Line emission

• From molecules– have additional energy levels because they can vibrate and rotate – This complicates their spectra… large numbers of vibrational and

rotational energy levels

2- Line emission

Note different appearance of single lines vs “bands” of lines.

What happens to the photon after the atom/molecule in material releases it? Answer depends DENSITY

If the material is TRANSPARENT ?then the photons can travel freely out of the matter.

… and then what? …

What is happening in this picture?What could I learn from the specific lines that I see?

What happens to the photon after the atom/molecule in material releases it? Answer depends DENSITY

If the material is OPAQUE?

then the photons bounce around, sharing their energy.They end up with a “thermalized” distribution of energies.

An analogy for “thermalized” photons (energy):

a single runner (photon)

running down an empty street:her speed is whatever she wants

moving down a crowded street:she bounces into the crowd, her speed gets closer and closer to the average speed of the people in the crowd.

… and then what? …

chapter 2 (2.3): the earth/moon/sun topics 1. moon phases 2. eclipses: shadows and visualizing the...

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