Download Monday Mar. 9 - University of Manitoba Physics Department

Phys 1830: Lecture 22
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test marks
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other marks
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Previous Class:
– Visualization: Computer Simulations
– Planetary Systems
This Class: Took up term test #2
– Solar System
Next Class:
• Solar System Formation
• Tour of the Solar System
Solar System Overview: Planet Definitions
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A. Classical Planet
1. Orbits the sun.
2. Massive enough that is own
gravity has caused its shape to
be nearly spherical.
3. It has “cleared the
neighbourhood” around its orbit
of other bodies.
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i.e. either by colliding with
(sweeping up) the debris in the
disk or by gravitationally kicking
the debris out of its path (slingshot
effect).
Solar System Overview: Planet Definitions
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A. Dwarf Planet
1. Orbits the sun.
2. Massive enough that is own
gravity has caused its shape to
be spherical.
3. Is not a satellite of another body.
(Has not cleared its
Examples:
neighbourhood.)
• Pluto
• Eris (1.3 * Pluto’s mass)
• Ceres (in the asteroid belt)
Objects at Neptune and beyond are called TransNeptune Objects (TNO) and those TNO that are
similar to Pluto are called plutoids.
Solar System Overview: What does the class already know about the classical planets?
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Note about T:
-273 C = 0 K
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• For each planet:
– revolve & rotate in the same
direction as other planets?
– primarily composed of rock or of
gas? # Earth Masses, # Earth radii
– small or large? (i.e. closer to Earth
size or Jupiter size?)
– in outer region or inner region of
solar system?
– hot or cold? surface T in Kelvin
– Lots of moons?
– Any other details are welcome 
(eg. Does it have rings? B field?)
Solar System Overview: Material for our contest!
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• The first 8 are planets.
• Note the second column.
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Solar System Overview
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• Keplerian Rotation Curve.
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Solar System Overview
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• The density in kg/m3
– 1000 for water; anything less than this floats in water.
– 2000-3000 for rocks and 8000 for iron
• Note the 2nd last column. Note the density of Earth.
• Which planets have densities like rocks/iron? Float on water?
Solar System Overview
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This classical planet would float if
there was a big enough bathtub
to put it in.
a) Pluto, because it is the smallest
planet.
b) Earth, because it has so much
water anyway.
c) Europa, because it is icey.
d) Saturn, because its density is less
than water.
Solar System Overview:
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• How do we know what we know about
our solar system?
1. Distances
2. Diameters
3. Masses
4. Densities
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Solar System Overview
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1. Distances from the Sun:
–
–
Radar
Kepler’s Third Law (empirical)
Orbits of planets are nearly circular  use Newton’s Laws for a
circular orbit of radius “r”. M is mass of sun.
Recall:
Rearrange:
Need velocity to get radius.
Solar System Overview: Distances
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• Velocity of Planets:
• v = distance/time
Distance:
The length of the path of the orbit is
the circumference of a circle.
Time: The time to travel the full orbit is the Period “P”.
Substitute in for distance and time:
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Solar System Overview: Distances
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• Substitute v squared into the
equation for radius:
Just need to observe the Period to get the distance!
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Solar System Overview: We have the distance!
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• Kepler’s Third Law
-- for ellipses
Observe the Period!
Using a in au and P in Earth years.
a == semi-major axis
Orbit of planet
sun
a
Solar System Overview
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• Keplerian Rotation Curve.
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Solar System Overview
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2. Diameters - from lecture 4
Linear diameter
angular diameter
--------------------- = ----------------------2 pi * Distance
360 degrees
2 pi * Distance
linear diameter = --------------------- * angular diameter
360 degrees
We can get the distance between a planet and Earth by using
step 1 to get its distance to the sun and then using geometry
to get the distance to the Earth. (In contemporary times, we
can use radar.) Then we just need to measure the angular
diameter and we have the size of the planet.
Also for radius of orbits.
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Solar System Overview
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3. Masses
Rearrange:
 use step 2 procedure.
Do this with a satellite around the planet.
For example the moon around the Earth.
Then “r” is the Earth-Moon distance and M
is the mass of the Earth. Velocity v is
determined from the Period of the moon’s
orbit (e.g. 1/12 of a year).
Solar System Overview
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4. Density
And for a sphere:
So
(Where R is radius.)
 Mass from step 3.
diameter
from step 2.
Solar System Overview: That is how
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do we know some of these values
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Solar System Overview: What does the class already know about the classical planets?
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Mass and Radius only
relative to Earth.
Temperature only in
Kelvin.
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• For each planet:
– Does it revolve in the same
direction as the other planets?
– Is it primarily composed of rock or
of gas?
– Is it small or large? (i.e. closer to
Earth size or Jupiter size?)
– Is it in the outer region or inner
region of the solar system?
– Is it hot or cold?
– Lots of moons or few?
– Any other details are welcome 
(eg. Does it have rings?) B field?
Mercury
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Messenger: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
Venus:
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Venus Express/European Space Agency
Ultraviolet Image
Earth
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Mars
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Mars Express/European Space Agency
Hebes Chasma
Jupiter
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New Horizons/NASA
IR image.
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Saturn
Cassini/NASA
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Uranus
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Voyager2/NASA
“True” Colour
False Colour
Neptune
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Voyager2/NASA
Question:
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• Which is the hottest planet in the
solar system?
a) Mercury because it is closest to
the sun.
b) Venus because its clouds cause
a runaway greenhouse effect.
c) Jupiter because it is like a ministar.