Download Picture Book of the Planets

The Solar System
The Sun
• Fuses 4 H atoms into 1 He, some mass  energy
• 75% hydrogen, 25% helium
• 99.8% of mass of solar system
• Middle-aged star, average in size, brightness, temperature
• Photosphere –
generates most of
the visible light
• Chromosphere –
middle layer,
visible during solar
eclipse
• Corona –
outermost atmosphere,
generates solar wind
Anatomy
of the Sun
• solar wind - (streams of
charged particles) causes
Northern Lights
• solar flares – outbursts
of UV, radio, X-ray
radiation, interrupt
radio, power on Earth.
Solar Flare
• prominences – large
arches of gas trapped by
magnetic fields.
sunspots – “cooler”
areas associated with
flares & prominences,
may affect Earth’s
climate. Sun Spots 1:50
Solar Features
The Development of Astronomy
• Aristotle – first to
propose that Earth
is round, based on
observations of the
round shadow it
cast on the moon
during lunar
eclipses.
The
Development
of Astronomy
• Eratosthenes - @ 200
B.C., accurately calculated
the circumference of the
Earth (39,400 km). Actual
circumference is 40,075
km.
• Geocentric (Earthcentered) model –
proposed by early
Greeks
• shows sun, moon,
and planets
(Mercury, Venus,
Mars, Jupiter,
Saturn) orbiting
stationary earth in
perfect circles.
Models of the
Solar system
Models of the Solar System
Problem: Geocentric Model did not explain
retrograde motion of planets.
Models of the
Solar System
• Mathematical
“proof” of
Geocentric Model
proposed by Greek
Claudius Ptolemy
in 150 A.D.
• Planets orbited in
epicycles while
orbiting Earth.
Could also have been used to
explain phases of Venus.
Models of the Solar System
• Heliocentric
(Sun-centered)
model – first
proposed by early
Greeks
• rejected because
it didn’t ‘feel’
like the Earth was
moving
The Dark Ages of Astronomy
• Few
advancements
made for
1,400 years
after Ptolemy.
The Birth of Modern Astronomy
• Heliocentric theory revived by Nicholas
Copernicus in 1543.
• Proven true, explains retrograde motion.
• Tycho Brahe –
@ 1575
persuaded king
of Denmark to
build him an
observatory.
• Measured
locations of
heavenly
bodies,
especially Mars,
far more
precisely than
anyone before.
The Birth
of Modern
Astronomy
The Birth of Modern Astronomy
• Kepler’s First
Law
• Kepler's Laws II
• Johannes Kepler
- @1600, Tycho
Brahe’s assistant
• Developed 3
Laws of
Planetary Motion
1) Planets move in
an ellipse with
the Sun at one
focus.
The Birth of Modern Astronomy
• Kepler’s Second Laws of Planetary Motion
2)A line between Sun and planet sweeps over
equal areas in equal time.
The Birth of Modern Astronomy
Johannes Kepler’s Laws of Planetary Motion
3)The square of a planet’s orbital period equals
the cube of its distance to the Sun. Kepler vs.
Brahe
The Birth of Modern Astronomy
Galileo Galilei – first to look into the sky with a
telescope and discover
• four moons orbiting Jupiter
• planets are circular disks, not points of light like stars
• Venus has phases, must orbit its source of light,
smallest at full phase, largest at crescent
• Moon’s surface not smooth, had mountains, craters, &
plains (“seas”)
• Sun had sunspots, tracked these to determine that the
Sun rotates once in just under a month.
• Work supported Copernicus’ view of universe.
The Birth of Modern Astronomy
Sir Isaac Newton – developed Universal Law of
Gravitation Gravity
• Every object in the universe attracts every other body
with a force proportional to product of their masses and
inversely
proportional
to the square of the
distance between
the centers of the
masses.
The Birth of Modern Astronomy
Sir Isaac Newton –
Laws of Motion
1) A body stays in a
state of rest or
uniform motion
unless an outside
force acts on it.
Newton's First Law of Motion
The Birth of Modern Astronomy
Sir Isaac Newton –
Laws of Motion
2) The net force (F)
on a body is
equal to its mass
(m) multiplied
by its acceleration
(a), F=ma.
The Birth of Modern Astronomy
Sir Isaac Newton –
Laws of Motion
3) Whenever one
body exerts a force
on a second body,
the second body
exerts an equal and
opposite force on
the first body.
The Birth of Modern Astronomy
Newton also
showed planets
are kept in
orbit by
balance of
gravity and
inertia.
The Birth of Modern Astronomy
Newton redefined Kepler’s Third Law,
• taking into account the masses of the bodies
involved
• Providing a method for determining the
mass of a body when the orbital period of
one of it’s satellites is known.
Movement of Planets
• Copernicus proposed that planets orbit Sun.
• Kepler showed orbits are elliptical.
• Newton showed planets are kept in orbit by
balance of gravity and inertia.
• Nebular Theory - swirling
sphere of dust and gas (from
exploded star) flattened into
disk
• matter at center became
protosun
• protoplanets formed from
clumps of matter
• protosun became hotter until
fusion started
• material spun off or knocked
off from planets became
moons
Formation of
Solar System
Structure
• Inner Planets
– have nickel-iron cores and rocky crusts, more dense
– few or no moons
• Asteroid Belt – between Mars & Jupiter – unformed
planet
• Outer Planets
– mostly gas, less dense
– numerous moons
– All have ring systems
• Kuiper Belt – beyond orbit of Neptune, many short-period
comets originate here
• Oort Cloud – theoretical – source of long-period comets?
Comets
• About 200 periodic comets known.
• Halley’s Comet returns every 76 years, first one
whose return was predicted.
• Made of ice and dust (“dirty snowballs”) left
over from early Solar System.
• Invisible except when near Sun (ice of nucleus
vaporizes, forms long tail, always points away
from sun).
• Elliptical orbits, most extend far beyond Pluto.
• Small nucleus, 16 x 8 x 8 km
Meteorites
• Bits of Solar System that have fallen to Earth
• May be iron, stone, or stony-iron (in space called
meteroids)
• several hundred tons enter atmosphere each day
• Meteors – glowing trail as they burn in atmosphere
• Meteor showers – when Earth passes through trail of
comet debris.
• Meteor Crater, AZ was formed by iron meteorite
30-50 m in diameter.
• Large one probably caused climate changes that led to
dinosaur extinctions.
Leonids
Meteor showers
are best after
midnight because
in the early
evening (A) we
are facing away
from the debris
cloud, and in the
early morning
(B) we are facing
toward it.
Tour of the Planets
Inner Planets - Mercury
• Closest to the sun, .38 AU.
• No atmosphere or satellites (moons).
• Slow rotation (3 rotations/2 revolutions), fast
revolution (59 days).
• Highly eccentric orbit.
• Most extreme temperature change - day/night
difference is 600° C (430°C/ -180°C.)
• Most heavily cratered; no plate tectonics.
• “Shriveled” surface, huge scarps (cliffs), highlands.
• Marias like moon – old lava floods after impacts.
Venus – 2nd from the Sun
•
•
•
•
•
•
•
•
•
•
.72 AU from sun.
Brightest planet in sky – cloaked in clouds.
Shows phases (like the moon).
No moons.
Slow, backwards rotation; day nearly = year.
Atmospheric pressure 90 times Earth’s.
97% CO2 atmosphere - runaway greenhouse effect.
Rains sulfuric acid.
Surface is hot enough to melt lead, 482o C, 900o F.
Volcanically active (shield volcanoes, runny lava).
Earth – 3rd from the Sun
•
•
•
•
•
•
•
•
1.0 AU (astronomical unit) from Sun
recognized as a planet in 16th century
core is hotter than surface of Sun
densest body in solar system
surface young because of plate tectonics
only planet with liquid water
Has one moon.
moon is gradually slowing our rotation
Mars –
th
4
from Sun
• thin atmosphere, no greenhouse effect
• temp. -207 to 80F, avg. –67 F
• Olympus Mons is highest mountain in solar
system; old volcano (volcanoes no longer active.)
• Valles Marineris is deepest, longest canyon in
solar system – would stretch from LA to NYC.
• water erosion evidence visible
• Core cooled faster than Earth’s, lost most of it’s
magnetic field & protection.
• two moons– Phobos and Deimos
The Asteroids
• mostly between Mars and Jupiter
• 7000+ known, some greater than 200 km
diameter
• total mass less than our Moon
• some planet moons may be captured
asteroids
• Near Earth Asteroids could hit Earth
Gas Giants – Jupiter –
•
•
•
•
•
•
th
5
from Sun
4 moons discovered by Galileo in 1610
Has many other moons, rings
90% H, 10% He
no surface, mostly liquid metallic hydrogen
would be a star if 80X larger
bands of high winds include permanent
storm called Great Red Spot
• huge magnetic field
Europa
•Smallest moon of Jupiter
•Has icy crust
•Thought to have liquid
oceans beneath, kept from
freezing by friction caused
by Jupiter’s gravity.
•Potential for life?
Io – innermost moon of Jupiter, very active sulfur volcanoes.
Ganymede, the largest moon in the solar system, bigger than
Mercury.
Saturn – 6th from Sun
• observed through telescope by Galileo in
1610
• rings discovered by Huygens in 1659,
thought to be unformed or shattered moon.
• least dense planet, density less than water
• more than 20 moons
Uranus – 7th from sun
• first planet discovered in modern times, by
William Herschel in 1781
• Explored by Voyager 2
• axis tilted nearly 90 degrees; has rings
• Greenish-blue due to methane gas.
• 15 or more moons (Miranda – extreme
terrain)
Neptune
• discovered from predictions based on
irregularities in orbit of Uranus
• sometimes the most distant planet
• similar to Uranus, mostly methane
• also has rings
• winds over 2000 km/hr are fastest in Solar
System
Pluto
•
•
•
•
Never visited by spacecraft
has one large moon named Charon
orbit highly inclined and eccentric
more similar to comet or asteroid than true
planet
• probably made of rock and ice
• temperature probably about -230 C
The End
This Solar System was brought to you by
Mr. Imes, with considerable help from
NASA space vehicles , the Hubble Telescope,
and the generous support of the U.S.
taxpayers.