Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
Sun, Earth, Moon
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Cartoon of the Day
“From now on we live in a world where man has walked on the Moon. It's not a miracle; we just decided to go. “
-- Tom Hanks
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Announcements
• HW Kepler, Gravity Light due
• CoC Star Party tomorrow
• Grading up to date!
Star Party
Join us for a
Friday,
OCT 16
7 – 9:30 p.m.Carl A Rasmussen AmphitheaterCollege of the Canyons Canyon Country Campus17200 Sierra Highway, Santa Clarita, CA 91351
COLLEGE OF THE CANYONS • Canyon Country Campus
STAR FORMATION: Light Beyond The VisiblePresented by Dr. Luisa RebullResearch Scientist, SSC and IRSA, IPAC, CaltechFeaturing: • Hands-on interactive demonstrations and activities
• COC student clubs and academic departments highlighting innovative approaches to understanding the science that governs the universe
• Gaze at the stars through a variety of telescopes
Food and beverages will be available for purchaseFor more information visit
www.canyons.edu/ccc • COL
LEGE OF THE CANYONS •
CANYON COUNTRY
Tallest TowerBuilding CompetitionSign-up online!
www.canyons.edu/Offices/CCC/Pages/StarParty.aspx
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Last Class
• Midterm debrief
• Multi-wavelength Astronomy
• Intro to the Solar System
• LT Sun Size (completed, not debriefed)
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
This Class
• Grade Status
• Debrief LT Sun Size & do questions
• Sun
• Earth
• Moon
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
Grade Status
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Grade Status
Letter Midterm Course
A 9 13
B 7 18
C 14 8
D 12 4
F 7 6
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
Debrief LT Sun Size
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The Sun has a diameter of approximately 1.4 million kilometers. Roughly how many Earths would fit across the diameter of the Sun?
A. 10
B. 100
C. 1000
D. 10,000
E. 1 million
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The image at right shows a picture of the Sun. The dark spots located on this image are sunspots. How does the size of Earth compare to the size of the sunspot that is identified on the right side of the image of Sun?
A. Earth and the sunspot are about the same size.
B. The sunspot is much, much larger than Earth.
C. The sunspot is much, much smaller than Earth.
Sun Size – Instructor’s Guide 129
© 2013 Pearson Higher Education, Inc. Instructor’s Guide for Lecture-Tutorials for Introductory Astronomy
Third Edition
diameter by that of the Moon. Here is an opportunity to talk about proportional reasoning skills.
9) [ 220 orbital diameters ]
Since 110 Sun diameters would fit between Earth and the Sun and 2 orbital diameters of the Moon would fit across the Sun, then 220 Moon orbital diameters would fit between the Sun and Earth.
ADDITIONAL QUESTIONS 1) The image at right shows a picture of the Sun. The dark spots located on this image are
sunspots. How does the size of Earth compare to the size of the sunspot that is identified on the right side of the image of Sun?
a) Earth and the sunspot are about the
same size. b) The sunspot is much, much larger than
Earth. c) The sunspot is much, much smaller than
Earth.
2) Which statement do you think best represents the size comparison between the diameter of the Sun and the distance between the Moon and Earth? The Sun’s diameter is a) smaller than the distance between the Moon and Earth. b) approximately equal to the distance between the Moon and Earth. c) larger than the distance between the Moon and Earth.
3) If you were constructing a scale model of the solar system that used a Sun that was the size of a basketball (approximately 12 inches in diameter), which of the following lengths would most closely approximate the scaled distance between Earth and the Sun? a) 3 feet (length of an outstretched arm) b) 10 feet (height of a basketball goal) c) 100 feet (height of an 10 story building) d) 300 feet (length of a football field)
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Which statement do you think best represents the size comparison between the diameter of the Sun and the distance between the Moon and Earth? The Sun’s diameter is
A. smaller than the distance between the Moon and Earth.
B. approximately equal to the distance between the Moon and Earth.
C. larger than the distance between the Moon and Earth.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
If you were to construct a scale model of the solar system that used a 2 cm cherry to represent the Moon, how large of a ball would you need to represent the Sun?
A. 4cm
B. 30cm
C. 110 cm
D. 440 cm
E. 880 cm
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
The Sun
THE SUN IS A STAR
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
What is a star?
• A sphere of hot gas
• mostly hydrogen & helium
• Interior hot enough to undergo nuclear fusion in core
• core above 107 K = 10 million K (18 million °F)
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Why Stars Shine
• Visible Sun is a hot layer of gas
• about 5800 K (5525°C, 9980°F)
• not as hot as the center!
• Gives off light the same way that hot metal glows red, yellow or white
• Thermal radiation or blackbody
• This is why stars have different colors
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Basic Data
• Fairly average star
• It rotates
• faster at the equator (25 days) than at the poles (31 days)
• Entirely gas: Hydrogen (80%) and Helium (19%)
• Central Temperature 15,000,000 K
• Surface Temperature 5800 K
http://www.kidsgeo.com/geography-for-kids/0003-how-big-is-the-earth.php
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
What Type of Star is the Sun?
• Main Sequence Star
• most stars spend most of their “life” on the Main Sequence
• energy source thermonuclear fusion
• H fusing to He in the core
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
What Type of Star is the Sun?
• Spectral Type G2
• Lifetime on Main Sequence 10 billion years
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The structure of the Sun
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The structure of the Sun
• Core
• compact: center to about 25% radius
• 15 million K
• atoms completely ionized
• e- “blasted off”
• Where thermonuclear fusion is taking place.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The structure of the Sun
• Radiative zone
• 0.25 - ~ 0.7 solar radii
• Energy from core transferred by EMR
• Convective zone
• above radiative zone
• Energy transferred to surface by convection
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Convection
Bubbles of hot gas rising up
Cool gas sinking down
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The Sun’s Luminosity comes primarily from
A. chemical burning
B. gravitational contraction
C. nuclear fusion
D. nuclear fission
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The energy produced by the Sun is produced
A. in a very small region at the center of the Sun
B. Uniformly throughout the Sun
C. At the surface of the Sun
THE OUTER LAYERS OF THE SUN
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The structure of the Sun
• Photosphere
• Visible surface of the Sun
• Apparently smooth layer of gas
• 500 km thick
• 5800 K
• Sunspots
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Granulation
• Up close, photosphere has a mottled appearance (granulation) due to convection cells.
• These cells form and fade and shift on a time scale of tens of minutes.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Sunspots
• well-defined surface areas that appear darker than their surroundings because of lower temperatures.
• Associated with sun’s magnetic field
• convection is inhibited by strong magnetic fields, reducing energy transport from the hot interior to the surface http://
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The structure of the Sun
• Chromosphere
• Atmospheric layer above the photosphere.
• 1000x fainter than the photosphere, but hotter!
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The structure of the Sun
• Chromosphere
• Pink color during a total eclipse.
• Filaments (dark regions) & Spicules/prominences (jets).
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Solar Prominence
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Sunspots appear dark because
A. They are holes in the photosphere allowing a view of deeper layers
B. Are large opaque structures that block the light from the interior
C. Are slightly cooler than the surrounding areas, appearing dimmer
D. Are burning holes in your retina
THE CORONA, SOLAR WIND AND SOLAR WEATHER
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The structure of the Sun
• Corona
• Outermost atmospheric layer.
• Extending outwards 20 times the Sun’s radius.
• Heated by magnetic field interactions.
• solar wind • 300 - 1000 km/s
• Loses 10 million tons/yr
http://antwrp.gsfc.nasa.gov/apod/ap080920.html
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Solar Weather
• In addition to sunspots, solar activity results in
• Solar flares
• Aurora Borealis
• Coronal Mass Ejections
• Geomagnetic Storms
• http://spaceweather.com/, http://www.swpc.noaa.gov/
(Ultraviolet images)
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Aurora Borealis
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Solar Weather and Humans
• Solar flares
• really refer to increased brightness
• Coronal Mass Ejection
• Interferes with Satellites
• Geomagnetic Storms
• In rare cases causes power grid issues
FATE OF THE SUN
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Endgame for our Sun
• A star’s fate is pretty much determined at the moment of it’s “birth” by its mass
• and the company it keeps
• High mass stars, ~ 8x Sun, explode
• supernovae
• Low mass stars like the Sun have a different fate
• Sun does NOT!!!!! “go supernova”
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Main Sequence to Red Giant
• After the core becomes depleted of H, the Sun will become a red giant
• A much larger, cooler star
• Earth, in all likelihood, gets swallowed up
Ar#sts concept of the Sun as a red giant:
Image: ESA
He core
H burning shell
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Red Giant to White Dwarf
• Eventually the red giant exhausts the H in its shell
• throws off up to half its mass
• “planetary nebula”
Spitzer Space Telescope Image of a PN the Helix Nebula
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Fading away...
• Core becomes a white dwarf
• Squeezed into size of Earth
• Maximally compressed into a degenerate gas
• In isolation, very slowly cools and fade away
Artist’s conceptImage ESA/NASA
Let’s Practice
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The Sun will ultimately
A. Go Supernova
B. Become a white dwarf
C. Become a black hole
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Which of the following are the most potentially damaging consequences of solar activity
A. Solar flares & Aurora Borealis
B. Coronal Mass Ejections & Geomagnetic storms
C. Promenences and Spicules
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
The Earth as a Planet
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Comparison of the “Terrestrial” Planets
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The “Habitable Zone”
• In astronomy and astrobiology, the habitable zone is the region around a star where a planet with sufficient atmospheric pressure can maintain liquid water on its surface.
www.astrobio.net
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Earth’s Statistics
• Equatorial Diameter = 12,756 km • Mass = 5.98 x 1024 kg • av. density = 5.5 g/cc • surface T = -50°C to +50°C • a = 1.00 AU • P = 1.00 year • e = 0.0167
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Earth’s Uniqueness
• Every major process on any rocky world in our solar system is represented in some form on Earth.
• Unique in 2 important ways
1. Surface water (75% of the surface is water)
• No other SS body has surface water currently
2. Life
• No other SS body has been found to have life. Yet.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Earth’s Early History
• Formed 4.6 billion years (4.6 x 109) ago from the inner solar nebula.
• 4 Stages of Evolution: • Differentiation
• Heavy Bombardment: Cratering
• Flooding
• Slow Surface Evolution
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Earth’s Structure — Core
• Hot as the Sun’s surface (~6000 K)
• Solid inner core
• liquid core surrounding it
• Source of Earth’s magnetic field
• Dynamo effect
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Earth’s Structure — Mantle
• Solid (“plastic”) Mantle
• As in deformable, not as in manmade
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Earth’s Structure — Crust
• Solid
• Thicker under land (60 km)
• thinner under oceans (10 km)
• Brittle: Broken into tectonic plates
• only terrestrial planet with plate tectonics
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Earth’s Magnetic Field
• Is Useful
• Likely helps birds & fish know where N and S are for migration
• Compasses
• Most importantly, it protects us from the solar wind
• which would otherwise slowly strip the Earth’s atmosphere away...which would NOT be good!
• Is generated by the dynamo effect
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Magnetic Field via Dynamo Effect
• 2 Key components
• Liquid conductor
• Rotation
• Earth
• ample liquid iron outer core, plus
• fairly brisk 24 hr rotation, yields
• strong magnetic field image from: http://www.abc.net.au
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The Core and the Dynamo
• Earth’s core consists mostly of iron + nickel
• high electrical conductivity.
• A conductor in motion creates a magnetic field
• The liquid core convects and the Earth Rotates
• Results in a dipole field
PLATE TECTONICS
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Plate Tectonics
• Plates are moved by convective motion in the mantle
• hot material rises and cools, cool material sinks
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Earth’s Tectonic History
LET’S PRACTICE
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
If the Earth’s rotation were to slow down drastically which of the following would most likely happen?
A. Runaway Greenhouse effect, leading to unsurvivable surface temperatures
B. Diminishment of Earth’s magnetic field, leading to loss of protection from the solar wind
C. Diminishment of atmospheric friction, leading to dramatic cooling of the surface
D. Diminishment of gravitational force, leading to loss of the Moon.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Plate tectonics exists on Earth because _____.
A. convection in the mantle causes motion
B. the crust is thin and broken into pieces
C. both of these
D. neither of these
EARTH’S TIMELINE
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
History of Geological Activity
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Earth’s Atmosphere
• 76% Nitrogen, 23% Oxygen, 1.3% Argon & a smattering of other stuff
• (water and carbon dioxide included).
• Ozone (O3) protects the surface from UV radiation (26 km up).
• Carbon Dioxide i s a “greenhouse gas:” it is transparent to visible light, but opaque to infrared light
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Evolution of Atmosphere
• Primordial Atmosphere
• Whatever was outgassed by the geologic activity (volcanoes) of ~4 billions years ago.
• carbon dioxide (CO2), nitrogen, water vapor.
• The CO2 levels decreased
• As Earth cooled, water vapor condensed. Oceans formed!
• The oceans absorbed CO2 (CO2 is soluble in water… think carbonated drinks!)
• The CO2 reacted with other elements in the water
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Evolution of Atmosphere
• O2 levels increased
• Initially, any oxygen present reacted with minerals to form iron oxide, etc…
• The rise of oxygen levels in the Earth’s atmosphere is tied to life.
• Specifically photosynthesis
• evolved 2.7 - 2.4 billion years ago
• picked up when the oceans developed plant life 2-2.5 billion years ago
• Oxygen exists because of life, not vice versa!
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Where Water Came From
• Not completely well understood. Several hypotheses:
• Older hypothesis: Primordial content and Vulcanism
• When a volcano erupts, 50-80 % of the gas is water vapor.
• Newer understanding: Primordial outgassing
• Earth formed so rapidly that it was substantially heated by the impacts of infalling material, as well as by radioactive decay.
• Molten surface -> continuous outgassing
• straight to the volcanic “ secondary atmosphere” without a hydrogen- rich primeval atmosphere.
• Some of the water may have arrived late in the formation as a bombardment of volatile-rich planetesimals
• studies of Comet LINEAR, which broke up in 1999 as it passed near the sun, support this
Astronomy 1 — Elementary Astronomy LA Mission College
Spring F2015
The Moon
The Moon
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Importance of the Moon
• Moderates wobble of Earth’s axis
• stabilizes climate
• Tides
• Cultural and Historical importance
• Only place aside from Earth we have visited in person
• Lunar Ranging
Image Credit: NASA
Galileo Image taken on way to Outer Solar
System
Apollo 16, Image Credit: NASA
CHARACTERISTICS OF THE MOON
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Moon Earth
• Equatorial Diameter = 3476 km
• mass = 7.35 x 1022 kg
• average density = 3.4 g/cc
• surface temp = -170°oC to
+130°C
• a = 384,400 km (from Earth!)
• P = 29.5 days (around Earth!)
• e = 0.055
• Equatorial Diameter = 12,756
km
• mass = 5.98 x 1024 kg
• average density = 5.5 g/cc
• surface temp = -50°C to +50°C
• a = 1.00 AU
• P = 1.00 y
• e = 0.0167
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Key Characteristics of the Moon
• No magnetic field
• Small core, no iron
• No atmosphere
• Too small & hot to hold onto gases
• gas molecules readily reach escape velocity!
• Very dry
• no sedimentary rock
• some ice may exist under the surface
Oblique View of the Lunar Crater Tycho
Credit: NASA/GSFC/Arizona State University
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The Moon: The View from Earth
• Tidally coupled to the earth
• rotation = revolution
• always see same side
• Heavily cratered highlands
• Smoother, darker lowlands
• maria (“seas”)
• flooded by lava
• Cool
Farside from LRO
Credit: NASA/GSFC/Arizona State University
Nearside from LRO
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Lunar Craters
• Numerous!
• >300,000
• Named after people: scholars, scientists, explorers
• Typical crater morphology Tycho
CopernicusKepler
Plato
Aristarchus
MareTranquillitatis
MareSerenitatis
MareCrisium
MareImbrium
Oceanus
Procellarum
MareNubium
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Lunar Maria
• large, dark, basaltic plains
• lava flooded low-lying areas
• more prevalent on near side
• 1.2-4.2 billion y.o.
• radiometric dating
• crater counting
Tycho
CopernicusKepler
Plato
Aristarchus
MareTranquillitatis
MareSerenitatis
MareCrisium
MareImbrium
Oceanus
Procellarum
MareNubium
LET’S PRACTICE
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
There is very little atmosphere on the Moon because
A. dry rocks on the moon absorb gases as soon as they are created.
B. it was blown away by meteor bombardment.
C. its low mass and high temperature allowed most gases to escape.
D. the gravitational tidal forces from the Earth stripped it away.
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The Moon
A. always points the same face towards the Sun.
B. does not rotate.
C. rotates at the same rate as the Earth rotates -- once per day.
D. rotates at the same rate as it revolves around Earth -- once per month.
LUNAR EXPLORATION
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
History of Lunar Exploration
• 1st visited by the USSR's Luna 1 and Luna 2 in 1959.
• These were followed by a number of U.S. and Soviet robotic spacecraft. US sent:
• Rangers (1961-1965) were impact probes,
• Lunar Orbiters (1966-1967) mapped the surface
• Surveyors (1966-1968) were soft landers.
• Apollo program -- Men on the Moon
• Lunar exploration resumed in the 1990s
• Clementine & Lunar Prospector
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Manned Lunar Exploration
• May 25, 1961 -- President John Kennedy committed the United States to landing a human being on the moon by 1970.
• Vehicle hefty enough to get to moon would be difficult to land: Two-module design with “disposable” lander • Command module
• The lunar landing module ( LM )
• The first human- piloted lunar landing was made July 20, 1969.
• July 1969 -- December 1972,: • 12 people reached the lunar surface
• collected 380 kg ( 840 lb) of rocks and soil
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Apollo Landing Sites
• First Apollo missions landed on safe, smooth terrain.
• Apollo 11: Mare Tranquilitatis; lunar lowlands
• Later missions explored more varied terrains.
• Apollo 17: Taurus-Littrow; lunar highlands
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
The Apollo Missions
• Hoax Believers, please check out Mr. “Bad Astronomy” Phil Platt’s extensive rebuttal:
• http://www.badastronomy.com/bad/tv/foxapollo.html
• And this filmmaker’s assessment of why faking it would have been harder than making it
• http://www.space.com/19531-moon-landings-faked-filmmaker-says-not-video.html
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Moon Landing Remastered
• http://video.nationalgeographic.com/video/news/space-technology-news/1969-moonlanding-vin/
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Moon Rocks
• Igneous (solidified lava)
• No sedimentary rock
Vesicular (= containing holes
from gas bubbles in the lava) basalts, typical of
dark rocks found in maria
Breccias (= fragments of different types of rock
cemented together), also containing anorthosites (= bright, low-density rocks
typical of highlands)
Older rocks become pitted
with small micrometeorite
craters.
LUNAR FORMATION
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Must Explain
• Similar oxygen isotopic composition to Earth
• But different chemical composition -- low density
• No magnetic field
• All igneous rock
• Same age as Earth
• Maria and Highlands
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Moon formation
• Fission Hypothesis
• Earth broke in two (if it were spinning quickly enough)
• Condensation Hypothesis
• Earth & Moon formed as a double planet system
• Capture Hypothesis
• Earth gravitationally captured a pre-existing body
• Large-impact hypothesis
• Early earth and moon formed from the glancing collision of two protoplanets
• Resulting large body became the earth and ejected debris formed the moon
• Could have caused Earth’s 23° tilt
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Large Impact Hypothesis
• Impacting body about the size of Mars — Theia
• Impact heated material enough to melt it
• consistent with “sea of magma”
• Collision not head-on
• Large angular momentum of Earth-moon system
• Collision after differentiation of Earth’s interior
• Different chemical compositions of Earth and moon
• Earth absorbed iron core of impactor
• Molten remnant material coalesced into Moon
LET’S PRACTICE
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Which proposed explanation for the Moon’s origin was ruled out when the Apollo mission revealed similar abundances of isotopes of oxygen in lunar rock as on Earth?
A. that the Moon broke off from the Earth
B. that the Moon and Earth formed together out of the same material
C. that the Moon was a passing body that was gravitationally captured by the Earth
D. that the Moon was formed when a large object impacted the proto-Earth
WRAP-UP
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Topic for Next Class
• Mercury, Venus, Mars
• Greenhouse effect
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Reading Assignment
• Astro: 7
• Astropedia: 8
Astronomy 1 - Elementary Astronomy LA Mission College Levine F2015
Homework
• No new HW yet