Solar System Physics

Astronomy 311Professor Lee

CarknerLecture 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=Gm1m2/r2

multiply distance by 2, decrease force

by 2 squared (4)

Using The Gravity Equation

G = 6.67 X 10-11 in units of (N m2/kg2)

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., 630000000000.0 = 6.3 X 1011

e.g., “6.3EE11” n.b., not “e”, “10x”, or “yx”

Always write on your paper using “X10” Also note, 6.3 X 1011 ≠ 6.311

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)