Origins of Modern Astronomy

Nebular Hypothesis (pg. 3)

–Solar nebula

»Large rotating cloud

»Mostly made of hydrogen and helium

»Made our solar bodies

Solar System formation Nebular hypothesis

• Nebula (cloud) rotates and collapses toward the center

• Cooling causes tiny solid particles

• Particles collide and form asteroid sized bodies to form terrestrial planets

• Lighter material and gases collect to form outer planets

Layers form on earth

• Decay of radioactive material and heat released by colliding material cause melting of interior

• Iron and nickel sink to interior

• Lighter material float out

• Gases escape to form atmosphere

Separation and Density Demo

• Why didn’t the solids separate?

• Why did the liquids separate?

• What state was Earth most likely in when it separated into layers

Quiz 1

1. Describe the Nebular Hypothesis

2. What state was the earth most likely in when it separated into layers?

Homework:

• Read pg. Section 2 Chapter 24

• Review pg. 683

Early AstronomySection 22.1

• Astronomy–Science of studying the universe•Properties of objects in space

•Laws of how the universe works

Golden Age600 BC-AD 150

Aristotle• Greek philosopher (384-322 BC)

• Earth is round

• Casts a curved shadow when

passes between sun and moon

His belief was abandoned during the Middle Ages

Eratosthenes276-194 BC

• First successful attempt to figure out the size of the earth

Hipparchus

2nd Century BC• Divided stars into six groups according to

brightness

• Method for predicting lunar eclipses

Geocentric model

• Moon, sun and planets orbit the earth

• Celestial sphere (stars) orbits the earth

• Incorrect

Heliocentric Model• Aristarchus (Greek

312-230 BC)• Earth and other

planets orbit the sun

ModelLocation of Earth

Location of Sun

Who supports

GeocentricCenter of the universe Orbits earth

Aristotle, Ptolemy

Heliocentric Orbits sunCenter of the universe

Aristarchus,

Copernicus

Ptolemaic System

• Claudius Ptolemy, wrote a 13 volume work on Greek astronomy

• Geocentric, used epicycles to explain the varying brightness of planets and planet retrograde motions

• Used mathematical terms to

explain the heavenly bodies

Nicolaus Copernicus1473-1543 (Poland)

• Earth is a planet like other planets

• Earth rotates

• Solar system with sun at the center

• Orbits were circular, was unable to improve how we predict where planets are located

Ptolemy and epicycles revisited

• http://astro.unl.edu/naap/ssm/animations/ptolemaic.html

Tycho Brahe1546-1601Denmark• Developed instruments to

measure the locations of heavenly bodies

• Collected a vast amount of data that Keplar was able to use

to build his laws of

planetary motion

Johannes Keplar1571-1630

• Three laws of planetary motion–Keplar observed:

• Mars orbit was elliptical

• As Mars approaches the sun it speeds up and slows down as it goes away from the sun

Three laws of planetary motion1. The path of each planet around the sun is an ellipse

with the sun at one focus.

2. Each planet revolves around the sun so that it sweeps over equal areas in equal amounts of time causing it to travel more rapidly in areas closer to the sun.

3. The square of the orbital period is proportional to the cube of its distance from the sun. (d3 = p 2)

Kepler’s laws

• http://www.astro.utoronto.ca/~zhu/ast210/kepler.html

Easy math

If planet A is 4 units from the sun then what is its orbital period. (d3 = p 2)

Another way to say them

• The path of the planets about the sun is elliptical in shape, with the center of the sun being located at one focus. (The Law of Ellipses)

• An imaginary line drawn from the center of the sun to the center of the planet will sweep out equal areas in equal intervals of time. (The Law of Equal Areas) http://www.physicsclassroom.com/mmedia/circmot/ksl.cfm

• The ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their average distances from the sun. (The Law of Harmonies)

Keplar’s laws

http://www.youtube.com/watch?v=5a2mcE-tzKE

http://www.youtube.com/watch?v=GcKiG-CuvtA

Let’s watch different planets in action

• http://astro.unl.edu/classaction/animations/renaissance/kepler.html

Astronomical UnitAU

• The average distance between the Earth and the sun.

• About 150 million kilometers• All other planets are measured in AU• Earth is 1 AU

Period of Revolution and Solar distances are found in table 1 on page 618 of the Earth Science Book

Visualizing an Astronomical Unit

• You need roll of adding machine tape

• Using the chart on page 618, mark off the distance in AU of each planet from the sun.

• Each meter will represent 10 AU. (so is 1 AU=1/10 meter=10 cm.)

Homework

Read 614-621

Do problems 1-7 (yes do the math practice!!!)

Galileo Galilei1564-1642

• Developed telescope• Discoveries

1. Four satellites around Jupiter which proved Earth was not the only center of motion

2. Planets are circular disks and not points of light

3. The moon’s surface was not smooth4. Sun has dark spots5. Retrograde motion is due to planets

passing the earth in their orbits

Galileo stated no force is required to keep an object in motion (inertia)

Venus Phases

How many phases does Venus go through?

What is the cause of these phases?

Retrograde motion

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::800::600::/sites/dl/

free/0072482621/78780/Retro_Nav.swf::Retrograde%20Mo

\

Galileo and Venus

• How did Venus retrograde motion definitely prove that the sun is at the center of the solar system?

• Turn to your table group and see if you can figure it out

Newton

• Mathematician

• Invented calculus to solve the gravity

Newton: Three laws of motion

Law 1:

An object at rest will remain at rest unless acted on by an unbalanced force. An object in motion continues in motion with the same speed and in the same direction unless acted upon by an unbalanced force. This law is often called "the law of inertia".

http://teachertech.rice.edu/Participants/louviere/Newton/law1.html

Law 2

• Acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated) the greater the amount of force needed (to accelerate the object).

• http://teachertech.rice.edu/Participants/louviere/Newton/law2.html

• Force=mass x acceleration

• Forceg=mass x gravitational acceleration

A little math

• If Marvin the Martian is 100 lbs on Earth how much would he weigh on the moon if the surface gravity is 17% of that on Earth?

Weight=mass x gravitational acceleration

Or weight = weight on earth x specific gravity

Now see if you can figure it out

W= 100 lbs x .17=17 lbs.

Law 3

• For every action there is an equal and opposite re-action.

• http://teachertech.rice.edu/Participants/louviere/Newton/law3.html

Sir Isaac Newton1642-1727

Newton in a nutshellWithout the influence of gravity,

planets would move in a straight line out into space.

The tendency of planets to remain in a straight line and the force of gravity result in elliptical patterns

Using Newton’s gravity

Basically

Force is proportional to the product of the mass of two objects/distance between them squared so:

If the mass doubles the force doubles but if the distance doubles then you have ¼ the force.

So you can figure weight of an object if you know the distance from earth

Another problem

If Marvin is 36 lbs how much is his weight if he is at 2r (distance from Earth)

Weight = 36/22 36/4=9lbs

So if this is true and astronauts at the space station are still within the

earth’s gravity, why do they experience

weightlessness???http://www.youtube.com/watch?

v=2V9h42yspbo

Vomit Comet

http://www.youtube.com/watch?v=2V9h42yspbo

So what did Einstein have to say about gravity?

But what is gravity, what is it that attracts to objects to one another? http://www.youtube.com/watch?v=O-p8yZYxNGc

http://www.youtube.com/watch?v=DbhuRcmSkMg&feature=related

Gravity as Curved Space