Solar System Physics Astronomy 311 Professor Lee Carkner Lecture 6

Physics and the Solar System  There are many physical effects that are important in shaping the solar system  We will concentrate on three:     There are, of course, others as well  e.g. photochemistry, radioactive decay, thermodynamics, etc.

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  Inverse square law  

Using The Gravity Equation  If mass is in kilograms and distance is in meters:    One newton is the force the Earth exerts on a 1/10 kg object on its surface

Gravitational Interaction  Gravity holds the planets and moons in orbit  Gravity can change orbits   All orbits have little perturbations caused by the other planets’ gravity   Gravity also can cause tidal effects

Tides  When gravity pulls more strongly on one part of an object than on another the result is a tidal force  Example: Tides on the Earth    Tries to stretch the Earth into a football shape 

High and Low Tide

Types of Tides  High tides and low tides happen twice a day   Sun also produces tides  Sun’s tidal force about 1/2 that of the Moon  Spring Tide --  Neap Tide --

Spring and Neap Tides

Synchronous Rotation  Why do we always see the same side of the moon?    The Earth’s gravity distorts the Moon, slowing its rotation 

Einstein and Gravity  Albert Einstein ( ) developed the General Theory of Relativity  Gravity is a curvature of spacetime caused by mass 

Gravitational Curvature of Spacetime

Changing Theories  We accept General Relativity because it has been (and will continue to be) tested   Newton’s Laws and Kepler’s Laws are still useful, they are just incomplete

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

Should We Believe Scientists?  Yes,   But,  Carkner’s Law:   Bottom line,  If you can’t evaluate yourself, be skeptical but look for consensus among scientists

Magnetic Fields  The Sun and many planets produce a magnetic field  A magnetic field exerts a force on moving charged particles   A magnetic field exerts a pressure   A magnetic field induces currents 

Magnetic Field Generation  Magnetic fields are generated by the dynamo effect  Moving charges produce magnetic fields   Generating a magnetic field requires a liquid interior   Magnetic fields are dipolar

Earth’s Magnetic Field

Solar Wind  The Sun’s magnetic field heats up its outer layers which produces a stream of fast moving ionized particles    Constant stream of ions flowing through solar system

Magnetosphere  A planets 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 

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 charged particles (pressure)  magnetosphere creates currents (induction)

Notes  Quiz #1 is next Monday (Sept 24)  Short answer and multiple choice  Covers lectures 1-8 (through “Origin of the Solar System”)