Solar System Physics Astronomy 311 Professor Lee Carkner Lecture 6

Notes  No class Monday (Sept 5)  Quiz #1 is the next Monday (Sept 12)  Short answer and multiple choice  Covers lectures 1-8 (through “Origin of the Solar System”)

Physics and the Solar System  There are many physical effects that are important in shaping the solar system  We will concentrate on three:    Impacts (when we talk about Mercury)

Newton’s Law of Universal Gravitation  Gravity -- a force that all objects exert on each other proportional to their mass and inversely proportional to the distance squared F=Gm 1 m 2 /r 2   multiply distance by 2, decrease force by 2 squared (4) 

Using The Gravity Equation   G = 6.67 X  in units of (N m 2 /kg 2 )   One Newton is the force the Earth exerts on a ~¼ pound object on its surface

Evaluating a Theory  Use the scientific method in detail   Use scientific reasoning    Rely on others who use the scientific method 

Scientific Notation   e.g., = 6.3 X   e.g., “6.3EE 11 ”  n.b., not “e”, “10 x ”, or “y x ”  Always write on your paper using “X10”   Also note, 6.3 X ≠

Tides   Example: Tides on the Earth   Moon pulls the center away from the far side  The tidal force tries to stretch the Earth into a football shape  This mostly effects the oceans

High and Low Tide

Types of Tides   The actual amount the water level changes is strongly dependant on geography and location  Sun also produces tides   Spring Tide -- Sun and Moon pulling together, strongest tides  Neap Tide -- Sun and Moon pulling against each other, lowest tides

Spring and Neap Tides

Synchronous Rotation   The moon is tidally locked   The Earth’s gravity distorts the Moon, slowing its rotation  Tidal bulge wants to be pointed at the Earth

Magnetic Fields   A magnetic field exerts a force on charged particles  Can manifest itself via:    Acceleration

Magnetic Field Generation   The dynamo effect requires:  liquid interior  conducting interior  reasonably fast rotation   As the liquid moves around, it carries ions with it, producing a current   Like an electromagnet  Magnetic fields are dipolar

Earth’s Magnetic Field

Solar Wind   Ions are missing electrons and so have a net charge   Sun’s magnetic field produces the solar wind, planet’s magnetic field deflects and traps the solar wind

Magnetosphere  A planet’s magnetic field interacts with the solar wind to produce a magnetosphere   Particles from wind get trapped in magnetic field   Size of magnetosphere changes as solar wind ebbs and flows

The Earth’s Magnetosphere

Charged Particle Belts  All planets with magnetic field have particle belts   The interaction of the particles and the magnetic fields produce currents   The moving particles collide with molecules in the atmosphere exciting them and producing light 

Next Time  Read Chapter 5 and 6.6

Summary  Physics  Gravity, impacts and magnetic fields are responsible for a wide range of solar system phenomena  Gravity  All solar system bodies effect each other gravitationally, but the effect is often small  Strong gravitational fields produce tides  Differential gravity creates bulges on opposite sides of a planet

Summary  Magnetic fields  liquid interior allows moving charges to generate field via dynamo  magnetosphere deflects solar wind (deflection)  magnetosphere traps solar wind charged particles (trapping)  magnetosphere creates currents of solar wind charged particles (acceleration)