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Our Solar System
Your Parents Solar System
21st Century Solar System
Who are some important astronomers?
Copernicus: first to state
moon orbited around
Earth and everything
revolved around Sun.
Also known as the
heliocentric model.
Galileo: observations of
Venus supported
Copernicus’ findings
Kepler: calculated that
planets had elliptical
orbit and planets closer
to Sun travel faster than
those farther away
Danish astronomer
Tyco Brahe (15461601) had an island
observatory and the
best measurements of
the positions for all
known planets
(Mercury, Venus,
Mars, Jupiter, and
Saturn) and the
Moon.
What did Tycho and Kepler discover?
At that time, many astronomers believed that
planets orbited around the sun in perfect
circles, but Tyco’s accurate measurements for
Mars didn’t fit a circle.
Instead, the mathematician Johannes Kepler
found that the orbit of Mars fit an ellipse the
best…
What is the first law of planetary
All planets orbit the sun in
motion?
an elliptical orbit.
2 foci
An ellipse is a geometric
shape with 2 foci instead
of 1 central focus, as in a
circle. The sun is at one
focus with nothing at the
other focus.
Eccentricity: 0= perfect
circle 1=elongated oval
FIRST LAW OF PLANETARY MOTION
Perihelion
Aphelion
Perihelion: When Mars or any another
planet is closest to the sun.
Aphelion: When Mars or any other
planet is farthest from the sun.
What is the second law of planetary
An imaginary line
motion?
A
B
But, areas A and B, swept out
by a line from the sun to
Mars, were equal over the
same amount of time.
drawn from the center
of the sun to the center
of the planet will sweep
out in equal areas in
equal intervals of time
Kepler also found that
Mars changed speed as
it orbited around the
sun: faster when closer
to the sun, slower
when farther from the
sun…
What is the third law of planetary
motion?
• Kepler found a relationship between the
time it took a planet to go completely
around the sun, and the average distance
from the sun
• What does this mean? As a planet/satellite
increases radius from the sun it takes longer to
make a revolution.
• For example: Mercury's orbital period is 88 days
and Plutos is 248 years.
Ellipse Demo
The Solar System:
List of Ingredients
Ingredient
Sun
Jupiter
Other planets
Everything else
Percent of total
mass
99.8%
0.1%
0.05%
0.05%
The Sun dominates our solar system
What is an Astronomical Unit?
• 1 AU: 150 million kilometers or 93 million miles
• Roughly the mean difference in distance
between the Sun and Earth
What are the Terrestrial Planets?
• Mercury, Venus, Earth & Mars
▫ “Earth-Like” Rocky Planets
▫ Largest is Earth
▫ Only in the inner solar system (0.4 to 1.5
AU)
• Rocky Planets:
▫ Solid Surfaces
▫ Mostly Silicates and Iron
▫ High Density: (rock & metal)
▫ Earth, Venus, & Mars have atmospheres
Mercury
Venus
Earth
Mars
What are the The Jovian (Gas Giant)
Planets?
Jupiter, Saturn, Uranus & Neptune
Largest Planets: at least 15 times mass of Earth.
Only in the outer solar system (5 to 30 AU)
No solid surfaces (mostly atmosphere)
Low density
Many moons
Gas Giants: (Jupiter & Saturn)
Thick H/He atmosphere, liquid hydrogen mantle,
ice core
Ice Giants: (Uranus & Neptune)
Ice/rock core & mantle, thin H/He atmosphere
Jupiter
Saturn
Uranus
Neptune
What are Dwarf Planets?
• Defined by the IAU in 2006
• Dwarf Planets:
▫ Ceres: first of the Asteroids, discovered in 1801
▫ Pluto: trans-Neptunian object discovered in
1930
▫ Eris: trans-Neptunian object discovered in
2005
▫ Haumea (trans-Neptunian, suspected)
▫ Makemake (trans-Neptunian, suspected)
What are the most giant moons in the
solar system?
• Moon: any natural satellite orbiting a planet or
dwarf planet
• Giant Moons:
▫
▫
▫
▫
Earth: The Moon (Luna)
Jupiter: Io, Europa, Ganymede, & Callisto
Saturn: Titan
Neptune: Triton
• Many smaller moons, both rocky & icy.
• Only Mercury & Venus have no moons.
What are Kuiper Belt objects?
Class of icy bodies orbiting beyond Neptune.
Found only in the outer Solar System
(>30AU)
Densities of 1.2 to 2 g/cc (mostly ices)
Examples:
Pluto & Eris (icy dwarf planets)
Kuiper Belt Objects (30-50AU)
Charon, Pluto’s large moon
Sedna & Quaor: distant large icy bodies
What are The Leftovers (small bodies)?
Asteroids: leftovers from the formation of the solar
system
Made of rock & metal (density 2-3 g/cc)
Sizes: Few 100km to large boulders
Most are found in the Main Belt (2.1-3.2 AU)
Meteoroids: material that falls toward Earth and enters
the atmosphere.
Bits of rock and metal
Sizes: grains of sand to boulders
Meteor: meteoroid that burns up in the atmosphere
creating a streak of light
Meteorite: meteoroid that collides with the ground
without burning up in the atmosphere.
Comets: small, icy bodies with eccentric orbits around the
sun.
Composite rock & ice “dirty snowballs”
Longs tails of gas & dust are swept off them when they
pass near the Sun.
Is Pluto and planet?
• What to consider?
• Size?
• Shape?
• Orbit?
• What is it made of?
What is the IAU Definition of a Planet?
In 2006, the International Astronomical
Union (IAU) came up with the following
definition of a planet:
 orbits the Sun
 has sufficient mass for its self-gravity to
overcome rigid body forces so that it assumes a
hydrostatic equilibrium shape (i.e., it is
spherical),
 has cleared the neighborhood around its orbit,
 is not a satellite
What is the IAU Definition of a Dwarf
Planet?
In 2006, the International Astronomical Union
(IAU) came up with the following definition of a
dwarf planet:
 orbits the Sun
 has sufficient mass for its self-gravity to overcome
rigid body forces so that it assumes a hydrostatic
equilibrium shape (i.e., it is spherical),
 has not cleared the neighborhood around
its orbit,
 is not a satellite