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Great ideas have their limitations…. Foundations of Modern Astronomy (and physics). Ancient Greeks Celestial Models Assumptions Earth stationary All motions around the Earth All motions are uniform, circular motions Is that such a big problem? Evidence for above assumptions?

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foundations of modern astronomy and physics
Foundations of Modern Astronomy (and physics)
  • Ancient Greeks
  • Celestial Models
  • Assumptions
    • Earth stationary
    • All motions around the Earth
    • All motions are uniform, circular motions
  • Is that such a big problem?
  • Evidence for above assumptions?
  • Time for some more animation…
laws theories hypothesis
Laws, Theories, Hypothesis

What is the difference?

What about

Natural Law

Scientific Law

Empirical Law

Are theories the end of the discussion?

claudius ptolemy 90 168
Claudius Ptolemy (90-168)
  • Years of previous models, data
  • Tweaked the models to fit data better
  • Still not perfect, but the best so far
  • So that’s all she wrote on that, right?
slide5

Epicycle

Mars

Equant

Earth

Deferent

nicolaus copernicus 1473 1543
Nicolaus Copernicus (1473-1543)
  • New view – Heliocentric
  • Not better!!!
johannes kepler 1571 1630
Johannes Kepler (1571-1630)
  • Finally got it right
  • Kepler’s 3 Laws of Planetary Motion
  • What do they tell us?
  • What don’t they tell us?
law 1 the orbits of the planets are ellipses with the sun at one focus
Law #1 – The orbits of the planets are ellipses with the sun at one focus.

Perihelion

Aphelion

Focus

Average distance = (distance from perihelion to aphelion)/2 =?

Average distance = 1 Astronomical Unit

law 2 a line from a planet to the sun sweeps over equal areas in equal intervals of time
Law #2 – A line from a planet to the sun sweeps over equal areas in equal intervals of time.

Huh?

Let’s try this – planets move faster when they are at perihelion than when they are at aphelion.

Velocity changes depending upon their distance from the sun.

Why?

law 3 a planet s orbital period squared is proportional to its average distance from the sun cubed
Law #3 – A planet’s orbital period squared is proportional to its average distance from the sun cubed.

Mathematically:

P2 a3

P2 = k a3 (k = constant)

Special formula –

If orbiting the sun

P in years, a in AU

P2 = a3

kepler s laws not just for breakfast anymore
Kepler’s laws – not just for breakfast anymore!

Actually not just for planets.

Kepler’s laws apply to anything orbiting

Moons orbiting planets

Comets orbiting the sun

Stars orbiting other stars

Stars orbiting around a galaxy

Galaxies orbiting other galaxies

Groups of galaxies orbiting other groups of galaxies

galileo galilei 1564 1642
Galileo Galilei (1564-1642)
  • Invented the telescope
  • Used the telescope and wrote about it!
  • Observations favored Kepler, not Ptolemy
isaac newton 1642 1727
Isaac Newton (1642-1727)
  • The ultimate nerd
  • Did NOT “invent” gravity
  • Did derive the 3 Laws of Motion
slide16
Law #1 – A body continues at rest or in uniform motion in a straight line unless acted upon by some force.

Huh?

Let’s try this -

  • Moving Things: straight line, steady pace
  • Non-moving things: well, nothing.
  • The above (1 & 2) remain that way unless something messes around with the things.
  • Change in motion is caused by a force.

(Change in motion = change in speed, direction)

slide17
Law #2 – A body’s change in motion is proportional to the force acting on it and is in the direction of the force.

Change in motion = acceleration (which can also be a deceleration)

Force  acceleration

Force = mass x acceleration

F = m a

Mass  weight

Mass = stuff, material, matter

slide18
Law #3 – When one body exerts a force on a second body, the second body exerts an equal and opposite force back on the first body.

Huh?

Cosmic Karma

“Little brother/sister rule”

Forces are a two way street – you get as good as you give…

newton s law of gravity
Newton’s Law of Gravity

F = force of gravity

negative = towards

G = constant

M= one mass, usually the larger

m = the other, usually the smaller

r = distance between centers of masses (usually centers)

ramifications of gravity
Ramifications of gravity
  • Limits?
  • Composition?
  • Changes in motion
    • Objects change direction (acceleration)
    • Objects change speed (acceleration)
  • Distance is squared!
  • Feel the effects of gravity?
  • Feel the same/different amounts of gravity?
orbits
Orbits
  • Objects orbit due to gravity
  • Change from straight motion to curved path
  • Can it explain Kepler’s Laws?
what isn t explained by newton
What isn’t explained by Newton?
  • How does gravity work?
  • What is actually causing the change in motion?
  • Is there “anti-gravity”?
  • Do Newton’s Laws explain all motions?
  • Did he invent the fig newton?
  • Time to shoot off Newton’s cannon!
light
Light
  • Almost all astronomical data is in this form!
  • More than just visible
  • Acts like a wave
    • Effected by velocity (Doppler effect)
    • Measureable wavelength, frequency, velocity
  • Acts like a particle
    • Photon=particle of energy
    • Amount of energy depends on wavelength/frequency
types of light
Types of light
  • Radio
  • Microwave
  • Infrared
  • Visible (ROYGBIV)
  • Ultraviolent
  • X-ray
  • Gramma-ray

How are they different?

Wavelength

Energy

DANGER!!!!

How are they the same?

VELOCITY!

Ultraviolet

Gamma-ray

spectra
Spectra
  • Interaction of light and matter
  • Why?
  • Light=Energy
  • Matter made up of atoms
  • Atoms made up of protons, neutrons, electrons
  • Electrons influenced by energy
slide26

e

p

slide27

e

p

atoms and light
Atoms and Light
  • Atoms can absorb light depending upon density
    • Individual atoms discretely absorb some light
    • More atoms (denser) absorb more types of light
    • Solid objects absorb most types of light
  • Atoms can emit light depending upon density
    • Individual atoms discretely emit some light
    • More atoms (denser) emit more types of light
    • Solid objects emit most types of light
spectrum
Spectrum
  • “Rainbow” but so much more
  • Light viewed in detail
    • Seen over a range of wavelengths
    • Seen over a range of frequencies
    • Seen over a range of photon energies
  • Type of spectra depends upon conditions
kirchhoff s laws
Kirchhoff’s Laws
  • Absorption Spectrum
  • Emission Spectrum
  • Continuous Spectrum
  • Type of spectrum reveals information on
    • Composition (possibly)
    • Temperature
    • Density
stellar spectra
Stellar Spectra

What type of spectrum is this?

use basic rules for spectra
Use basic rules for spectra
  • If the spectra shows features for an element, the element is present.
  • If the spectra doesn’t show the feature for the element, then the element isn’t present.
  • Spectra sorted according to elements presence/absence/unique features.
slide36
But…

“Absence of evidence is not evidence of absence” – Carl Sagan

Are elements present/absent for another reason?

Yes – temperature!

Re-arrange those spectra!

slide37

Hottest

Coolest

slide38

Coolest

But they have already been named/labeled!

Just rearrange the order of the labels

Hottest

spectral classification system
Spectral Classification System
  • Classifies stars according to TEMPERATURE
  • Ordered from Hottest to Coolest
  • Originally included only those visible to eye
  • Extends to IR types now

OBAFGKMLT

  • More detail with B0, B1, B2, etc
  • Sun = G2
fusion confusion
Fusion Confusion
  • Not fission
  • Energy released by fusing atoms
    • Only useful for low mass atoms (<Fe)
    • Creates more complex atoms
    • Difficult to do
      • High Density
      • High Temperature
slide41

+

Deuterium

n

slide43

Proton

Helium 4

Proton

what does it all mean
What does it all mean?
  • Mass  Energy
  • Hydrogen  Helium
  • Evidence?