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? –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? The earth spins! –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? 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) A siderial day is defined as the time it takes the Earth to make a complete spin on its axis relative to distant stars A solar day is defined as the time it takes the Earth to do a complete spin on its axis relative to the Sun 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

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?

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, Eclipses – Lunar

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? 2- Eclipses – Lunar

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? 2- Eclipses – Solar

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 2- Eclipses – Solar

Solving the Mystery of Planetary Motion (use of the Scientific Method) * Visualize in 3D!* Ask “How do we know?”

1. Observe / Question 2. Hypothesize / Explain 3. Predict 4. 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.) Kepler’s Three Laws of Planetary Motion

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 2 nd 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 Three Laws of Planetary Motion

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. distance 3 = distance * distance * distance (time to orbit) 2 = (time to orbit) * (time to orbit) Kepler’s Three Laws of Planetary Motion 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 Energy Topics 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?

How light (= energy) and matter interact A.What is the structure of matter? Atoms = Nucleus + Electron cloud Nucleus contains protons (p) and neutrons(n) Electrons (e) sort of “orbit” the nucleus

How light (= energy) and matter interact A.What is the structure of matter? 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)

How light (= energy) and matter interact A.What is the structure of matter? Atoms = Nucleus + Electron cloud Nucleus contains protons (p) and neutrons(n) Electrons (e) sort of “orbit” the nucleus q= charge r = distance between like charges repel each other, opposite charges attract atoms will attract electrons until net charge = 0 (#p’s = #e’s) ! 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 (H 2 O, CO 2 ) How light (= energy) and matter interact A.What is the structure of matter?

Isotope: same # of protons but different # of neutrons. ( 4 He, 3 He) How light (= energy) and matter interact A.What is the structure of matter?

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.. How light (= energy) and matter interact A.What is the structure of matter? B.How is energy stored in atoms?

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 How light (= energy) and matter interact A.What is the structure of matter? B.How is energy stored in atoms?

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 How light (= energy) and matter interact A.What is the structure of matter? B.How is energy stored in atoms? 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) How light (= energy) and matter interact A.What is the structure of matter? B.How is energy stored in atoms? C.What is light: photons or waves?

“wave/particle duality” How light (= energy) and matter interact A.What is the structure of matter? B.How is energy stored in atoms? C.What is light: photons or waves?

A wave is a pattern of motion that can carry energy without carrying matter along with it Wavelength =  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 =  * f How light (= energy) and matter interact A.What is the structure of matter? B.How is energy stored in atoms? C.What is light: photons or waves?

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) How light (= energy) and matter interact A.What is the structure of matter? B.How is energy stored in atoms? C.What is light: photons or waves?

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 How light (= energy) and matter interact A.What is the structure of matter? B.How is energy stored in atoms? C.What is light: photons or waves?

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? …