Lecture 2 -- Deep Distance
Tuesday June 4
Most of the stars rotate about in the sky, rising in E, setting in W
Stars trace circles in the sky E to W
N stars circle, S stars dip below the horizon
Celestial equator
N, S celestial poles
Meridian
Zenith
Path of the sun -- in winter--ecliptic
Path of the sun -- in summer
Path of the sun -- in spring and fall
Each night, the same stars come up, but 4 minutes earlier. After one
year, all the little 4 minutes add up, and we see the same sky
Constellations are groupings of stars that they associated with the seasons
Planets --go roughly along the line with the sun, the ecliptic.
The Moon also goes roughly along the ecliptic
Planets -- 2 wanderers stayed close to the sun, tracing back and forth
The other 5 wanderers seem to go all the way around the sky, but took
a strange loop in the sky. This confused the ancients, and probably
was responsible for the concept of epicycles, or circles within circles,
to explain celestial motions
W of the sun -- planets rise as morning stars
E of the sun -- we see planets in the evening
Spring Equinox -- March 21 (Vernal Equinox) 'Hope'
Sun crosses the equator and goes N
Summer Solstice -- June 21, 'Celebration'
Sun reaches farthest N, and is highest in the sky
Important to ancient cultures -- max daylight, brightness, sense
of long, lazy summers
Autumn Equinox -- Sept 22, 'Preparation'
Sun crosses the celestial equator, going S
Winter Solstice -- Dec 21, 'Hibernation'
Sun furthest S of celestial equator, lowest in the sky
Moon: races through the sky and goes through phases (interactive animation)
Moon close to the sun -- New Moon, a crescent
1 week later, Moon at right angle to Sun, a half circle Quarter Moon
Overhead at sunset, sets at midnight
Waxing -- increasing in size
Terminator -- line between light and dark
1 week later Moon opposite sun, Full Moon
Rising at sunset, all through the night, sets at sunrise
1 week later Moon at right angle to Sun, half circle Three Quarter Moon
Rises at midnight, we see it in the morning sky, sets at midnight
Waning -- decreasing in size
What was their cosmology? The beginnings of trying to explain the Universe
Aristotle -- 350 BC
With Plato, developed rational thought and rudiments of scientific method
But they thought very highly of absolute symmetry, simplicity, and an
abstract idea of perfection
Earth at the center of the Universe
Universe was spherical and finite
Planets and stars moved on spherical shells
Spherical Moon -- Curvature of Moon's terminator
Model-Experiment-Test-Refine
Sun farther than Moon, because the Moon passes between the Sun and Earth -- a recognition of the meaning of lunar phases (interactive animation).
Spherical Earth: Moon was a sphere, and, as you go N, stars sink below the horizon
But Earth is at the center of the Universe, because the stars didn't move
Error: Problem with distance scales, inability to abstract
Hipparchus -- 130 BC -- Considered the first real astronomer
Observed the positions of stars and planets, and recorded them
Could PREDICT position of sun and moon
Discovered wandering of the northern focus of sky motion - Precession
But Chinese were recording positions as early as 1000 BC
Ptolomy -- 150 AD
Circular orbits around the Earth: Moon, Mercury, Venus, the Sun, Mars, Jupiter and Saturn
Because planets don't move at constant rates, he said the circles were offset from each other, and that planets moved in epicycles
Could explain all the motions in the sky to pretty good precision
Wrote the Almagest, the Bible of ancient astronomy for 1000 years
His work remained at the Great Library of Alexandria in Egypt, until it was plundered by Arabs.
The Arabs took the knowledge and named the stars. Most names are arabic. Constellations are in Latin. Planets are in Latin
Copernicus -- 1500
Applied Occam's Razor: Among competing theories, the best is the simplest theory, the one with the fewest assumptions
Aesthetic problems with so many little epicycles
Correctly concluded from the inaccuracies in Ptolemaic model that the sun was at the center of the solar system
Inferior planets and superior planets
Copernicus died before his revolution, but Giordano Bruno died because of his revolution
Tycho Brahe -- 1600
With funds from King of Denmark, built Uraniborg (Sky Castle) on his own private island
Measured stars very accurately
Detected shift in stars over seasons -- parallax
Remained a Ptolemaist, but pounded the nail in the coffin of Brahe
Johannes Kepler -- 1600
Inherited the detailed records
Addressed the question of Mars' motion, because of its pronounced retrograde cycle (interactive animation).
Came up with Kepler's Laws
1. Each planet moves in an ellipse, with Sun at one focus
2. Line between sun and planet sweeps equal areas in equal time
3. ratio of cube of the semimajor axis to square of period is the same for each planet
Galileo Galilei -- 1610
Saw phases of Venus and moons around Jupiter
Sun was at center -- some things revolved around something other than Earth
Saw the planets as WORLDS
Isaac Newton -- 1700
'Saw futher because he stood on the shoulders of Giants"
Deduced that white light was made up of colors (split with prism)
Looked for the laws that made the Universe tick, not just mechanics
Newton's Universal Law of Gravitation
Every particle in the Universe attracts every other particle
with a force proportional to their masses and inversely
proportional to the square of the distance between them
Newton's Laws of Motion
1. A body at rest stays at rest, and a body in motion moves at constant speed in a straight line unless a force acts upon it
2. A force acting on a body causes it to accelerate in the direction of the force and inversely proportional to the mass of the body
3. For every force on a body, there is an equal and opposite force acting on another body
The solar system, slightly elliptical orbits, stars very far away. Santa Fe in our model solar system -- Alpha Centauri
Moon: Demo of New, First Quarter, Full and Last Quarter
Same face is always facing us
Seasons: Due to the tilt of the Earth's axis as it goes around the Sun
Northern Summer: N pole is tilted towards the sun
at the same time, it is Southern Winter
Northern Winter: N pole is tilted away from the sun
Parallax -- Apparent seasonal shift of nearby stars due to the Earth's motion around the sun
Constellations change with the seasons, because the background stars change as the direction we look out into changes with our orbit around the sun
White light is actually composed of all the colors mixed together
Colors can be spread out with a prism -- Isaac Newton
Specific colors can be removed from a beam of light by intervening atoms
Caused by the absorption of light at specific colors, due to electrons around the atoms
Each type of atom has a unique fingerprint, or pattern of dark lines that it can remove from the spectrum
VIDEO: THE FILMS OF CHARLES AND RAY EAMES: VOLUME1 - POWERS OF TEN
6/4/96