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?
What is the difference?
Are theories the end of the discussion?
Average distance = (distance from perihelion to aphelion)/2 =?
Average distance = 1 Astronomical Unit
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.
P2 = k a3 (k = constant)
Special formula –
If orbiting the sun
P in years, a in AU
P2 = a3
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
Let’s try this -
(Change in motion = change in speed, direction)
Change in motion = acceleration (which can also be a deceleration)
Force = mass x acceleration
F = m a
Mass = stuff, material, matter
“Little brother/sister rule”
Forces are a two way street – you get as good as you give…
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)
How are they different?
How are they the same?
What type of spectrum is this?
“Absence of evidence is not evidence of absence” – Carl Sagan
Are elements present/absent for another reason?
Yes – temperature!
Re-arrange those spectra!
But they have already been named/labeled!
Just rearrange the order of the labels