Transcript Origins of Modern Astronomy

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 Astronomy
Section 22.1
• Astronomy
–Science of studying the
universe
• Properties of objects in space
• Laws of how the universe works
Golden Age
600 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
Eratosthenes
276-194 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
Model
Geocentric
Heliocentric
Location of
Earth
Location of
Sun
Who
supports
Center of
the universe
Orbits earth
Aristotle,
Ptolemy
Orbits sun
Center of the
universe
Aristarchus,
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 Copernicus
1473-1543 (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/p
tolemaic.html
Tycho Brahe
1546-1601
Denmark
• 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 Keplar
1571-1630
• 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 motion
1.
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.
The square of the orbital period is proportional to the
cube of its distance from the sun. (d3 = p 2)
3.
Kepler’s laws
• http://www.astro.utoronto.ca/~zhu/ast210/k
epler.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=5a2mcEtzKE
http://www.youtube.com/watch?v=GcKiGCuvtA
Let’s watch different planets in
action
• http://astro.unl.edu/classaction/animations/
renaissance/kepler.html
Astronomical Unit
AU
• 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 Galilei
1564-1642
•
•
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 smooth
4. Sun has dark spots
5. 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.mcgrawhill.com/olcweb/cgi/pluginpop.cgi?it=swf::80
0::600::/sites/dl/free/0072482621/78780/Ret
ro_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/lo
uviere/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/lou
viere/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/lou
viere/Newton/law3.html
Sir Isaac Newton
1642-1727
Newton in a nutshell
Without 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=Op8yZYxNGc
http://www.youtube.com/watch?v=DbhuRcm
SkMg&feature=related
Gravity as Curved Space