A100 solar system
This presentation is the property of its rightful owner.
Sponsored Links
1 / 28

A100 Solar System PowerPoint PPT Presentation


  • 81 Views
  • Uploaded on
  • Presentation posted in: General

A100 Solar System. Review Chapter 1, Kepler’s Laws Read Chapter 2: Gravity & Motion 2 nd Homework due Sept. 26 Rooftop Session Tuesday evening, 9PM Kirkwood Obs. open Wednesday Eve., 8:30-10:30 IN-CLASS QUIZ ON WEDNESDAY!!. Today’s APOD. The Sun Today. Today: the Equinox.

Download Presentation

A100 Solar System

An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -

Presentation Transcript


A100 solar system

A100 Solar System

  • Review Chapter 1, Kepler’s Laws

  • Read Chapter 2: Gravity & Motion

  • 2nd Homework due Sept. 26

  • Rooftop Session Tuesday evening, 9PM

  • Kirkwood Obs. open Wednesday Eve., 8:30-10:30

  • IN-CLASS QUIZ ON WEDNESDAY!!

Today’sAPOD

The Sun Today


Today the equinox

Today: the Equinox

11:44 AM EDT

today

Dr. Phil Plait (Sonoma St. U.) acting as the Bad Astronomer balanced three raw eggs on end in late October 1998

http://apod.nasa.gov/apod/ap030923.html


The problem retrograde motion

The Problem: Retrograde Motion

  • In a simple geocentric model (with the Earth at the center), planets should drift steadily eastward through the sky against the background of stars

  • But sometimes, the motion of the planets against the background stars reverses, and the planets move toward the west against the background stars


Retrograde motion in a geocentric model

Retrograde Motion in a Geocentric Model

  • Ptolemy accounted for retrograde motion by assuming each planet moved on a small circle, which in turn had its center move on a much larger circle centered on the Earth

  • The small circles were called epicycles and were incorporated so as to explain retrograde motion


Epicycles get more complex

Epicycles did pretty well at predicting planetary motion, but…

Discrepancies remained

Very complex Ptolemaic models were needed to account for observations

More precise data became available from Tycho Brahe in the 1500s

Epicycles could not account for observations

Epicycles get more complex


Astronomy in the renaissance

Astronomy in the Renaissance

  • Could not reconcile Brahe’s measurements of the position of the planets with Ptolemy’s geocentric model

  • Reconsidered Aristarchus’s heliocentric model with the Sun at the center of the solar system

Nicolaus Copernicus (1473-1543)


Heliocentric models with circular orbits

Heliocentric Models with Circular Orbits

  • Explain retrograde motion as a natural consequence of two planets (one being the Earth) passing each other

  • Copernicus could also derive the relative distances of the planets from the Sun


But a heliocentric model doesn t solve all problems

But a heliocentric model doesn’t solve all problems

  • Could not predict planet positions any more accurately than the model of Ptolemy

  • Could not explain lack of parallax motion of stars

  • Conflicted with Aristotelian “common sense”


Johannes kepler 1571 1630

Using Tycho’s precise observations of the position of Mars in the sky, Kepler showed the orbit to be an ellipse, not a perfect circle

Three laws of planetary motion

Johannes Kepler (1571-1630)


Kepler s 1 st law

Kepler’s 1st Law

  • Planets move in elliptical orbits with the Sun at one focus of the ellipse

  • Words to remember

    • Focus vs. Center

    • Semi-major axis

    • Semi-minor axis

    • Perihelion, aphelion

    • Eccentricity


Definitions

Definitions

  • Planets orbit the Sun in ellipses, with the Sun at one focus

  • The eccentricity of the ellipse, e, tells you how elongated it is

  • e=0 is a circle, e<1 for all ellipses

e=0.02 e=0.4e=0.7


Eccentricity of planets dwarf planets

Eccentricity of Planets & Dwarf Planets

Which orbit is closest to a circle?


Kepler s 2nd law

Kepler’s 2nd Law

  • Planets don’t move at constant speeds

  • The closer a planet is to the Sun, the faster it moves

  • A planet’s orbital speed varies in such a way that a line joining the Sun and the planet will sweep out an equal area each month

  • Each month gets an equal slice of the orbital pie


A100 solar system

Kepler’s 2nd Law:


A100 solar system

Same Areas

If the planet sweeps out equal areas in equal times, does it travel faster or slower when far from the Sun?


Kepler s 3 rd law

Kepler’s 3rd Law

  • The amount of time a planet takes to orbit the Sun is mathematically related to the size of its orbit

  • The square of the period, P, is proportional to the cube of the semimajor axis, a

P2 = a3


Kepler s 3 rd law1

Kepler’s 3rd Law

  • Third law can be used to determine the semimajor axis, a, if the period, P, is known, a measurement that is not difficult to make

  • Express the period in years

  • Express the semi-major axis in AU

P2 = a3


Examples of kepler s 3 rd law

Examples of Kepler’s 3rd Law

  • Express the period in years

  • Express the semi-major axis in AU

For Earth:

P = 1 year, P2 = 1.0

a = 1 AU, a3 = 1.0

P2 = a3


Examples of kepler s 3 rd law1

Examples of Kepler’s 3rd Law

For Mercury:

P = 0.2409 years

P2 = 5.8 x 10-2

a = 0.387 AU

a3 = 5.8 x 10-2

P2 = a3

  • Express the period in years

  • Express the semi-major axis in AU


Examples of kepler s 3 rd law2

Examples of Kepler’s 3rd Law

For Venus:

P = 0.6152 years

P2 = 3.785 x 10-1

What is the

semi-major axis

of Venus?

P2 = a3

a = 0.723 AU

  • Express the period in years

  • Express the semi-major axis in AU


Examples of kepler s 3 rd law3

Examples of Kepler’s 3rd Law

For Pluto:

P = 248 years

P2 = 6.15 x 104

What is the

semi-major axis

of Pluto?

P2 = a3

a = 39.5 AU

  • Express the period in years

  • Express the semi-major axis in AU


Examples of kepler s 3 rd law4

Examples of Kepler’s 3rd Law

The Asteroid

Pilachowski (1999 ES5):

P = 4.11 years

What is the semi-major axis

of Pilachowski?

P2 = a3

a = ??? AU

  • Express the period in years

  • Express the semi-major axis in AU


Fill in the table

Fill in the Table

  • Express the period in years

  • Express the semi-major axis in AU


Comparing heliocentric models

Comparing Heliocentric Models


Geocentric heliocentric

Geocentric > Heliocentric

  • The importance of observations!

    • When theory does not explain measurements, a new hypothesis must be developed; this may require a whole new model (a way of thinking about something)

    • Why was the geocentric view abandoned?

    • What experiments verified the heliocentric view?


Assignments this week

ASSIGNMENTSthis week

  • Review Chapter 1, Kepler’s Laws

  • Read Chapter 2: Gravity & Motion

  • 2nd Homework due Sept. 26

  • Rooftop Session Tuesday evening, 9PM

  • Kirkwood Obs. open Wednesday Eve., 8:30-10:30

  • IN-CLASS QUIZ ON WEDNESDAY!!


  • Login