Astronomy 3040
Astrobiology
Spring_2016
Day-4
Homework -1
 Due Monday, Feb. 8
 Chapter 2:
 1, 3, 16
 23, 24, 26
 29, 30, 33
 44
 53, 54, 56
 The appendices will be useful
Life Beyond Earth - History
 If you go out to a dark location at night and look up (for a
few years), what do you see?
 Sun rises and sets every day; moves across the sky
 Stars rise and set every day; move at a slightly different rate
than Sun ==> Different stars visible at different times.
 Moon goes through monthly phases
 Planets meander in a “mysterious manner”
 No wind
Conclusions?
 The Earth is flat and motionless.
 But we know the Sun controls life (day/night)
 The Moon influences tides
 Stars are useful for timing agriculture
 Lots of ties to daily life and ritual
Greeks
 By ~500 B.C.E. the Greek society was well established and
philosophy was began.
 Thayles (~624-546 BCE) origin of Greek science
 What is the Universe made of?
 Plato & Aristotle - 3 tenets of modern science.
 1. Try to understand nature w/o supernatural expl.
 2. Mathematics, geometry.
 3. Power of reasoning from observations.
 ==> Models
The Greek Universe
 Geocentric
 Celestial Sphere
 Ptolemaic model (100-170 A.D.)
 Epicycles
 Aristarchus (310-230 B.C.E.)
 Heliocentric – had it right!
 But disagreed with Aristotle
 Could not measure parallax!
Heliocentric Universe
 Anti-intellectual fervor of 5th Century
 Libraries destroyed, The Church came to power
 Islamic scholars saved and translated much of Greek
 Contact with Hindu scholars, interaction with Chinese
 Nicholas Copernicus (1473-1543)
 Aware of Aristarchus's work
 Advocated the heliocentric view
 Tycho Brahe (1546-1601)
 Observational data
 All done with naked eye
Heliocentric Universe
Johannes Kepler (1571-1630)
 3 Laws of Planetary Motion
 1. Elliptical orbits, Sun at one focus
 2. Equal area in equal time
 3. P2 = ka3 (P in years, A in Astronomical Units)
Heliocentric Universe
 Galileo Galilei (1564-1642)
 Laid foundations of modern physics
Inertia (later explained by Newton's 1st law)
 Gravity
 First to use a telescope for astronomical purposes
 1. Sunspots – Sun was not a perfect surface.
 2. Craters on Moon – Moon was not a perfect surface.
 3. Observations of thousands of stars not visible by eye.
 So stars more numerous than Tycho thought.
 4. Geocentric Universe death
 Four moons orbiting Jupiter
 Phases of Venus

Modern Science
 Isaac Newton (1642-1727)
 1687 – Principia – precise math descriptions
 3 Laws of Motion
 Universal Law of Gravitation
 Invented Calculus (to prove Kepler's Laws)
 Developed new type of telescope
The Life Debate - Greeks
 Thayles - What is the Universe made of?
 2 schools of thought
 Life must be everywhere, abundant
 No way, Jose!
 Anaximander – other Earths at other times.
 Greeks
 Atomists (many worlds)
 Aristotelians (Earth is unique, center of everything)
The Life Debate –
Copernican Revolution
 Copernicus proved the Earth was not the center
 Aristotle was wrong.
 Galileo – lunar features could be land & water.
 Kepler – moon had an atmosphere, and inhabited by
intelligent beings.
 W. Herschel – assumed all planets inhabited.
 Lowell – canals on Mars.
 Based on hope & beliefs, not real evidence.
Modern Science
 The Scientific Method.
 Observations
 Question
 Hypothesis
 Prediction
 Test
 Revise/More
Predictions
Modern Science
 OR The Eureka Moment.
 Look at Nature in a “general way”
not looking for anything in specific
 Galileo
 Voyager 1, 2 - Europa

 Must overcome “personal experience”
 Gravity doesn't “work” because of drag.
Hallmarks of Modern Science
1. Modern science seeks explanations for observed
phenomena that rely solely on natural causes.
2. Science progresses through the creation and testing
of models of nature that explain the observations as
simply as possible.
3. A scientific model must make testable predictions
about natural phenomena that would force us to
revise or abandon the model if the predictions do not
agree with observations.
Modern Science
 Occam's Razor
 William of Occam (1285 - 1349)
 K.I.S.S.
 Verifiable Observations
 UFOs vs. Einstein Theory of Relativity
 Science, Nonscience, Pseudoscience
 Objectivity
 Scientific Theory
 Newton, Darwin, Einstein
Gravity
 1666 – Newton

Apple & tree ==> Moon & Earth
 Universal Law of Gravitation

Every mass attracts every other mass through a
force called gravity.

Directly proportional to product of masses.

Inversely proportional to square of distance
between them.
G = 6.67 X 10-11 m3/kgs2
Force is in Newtons
F = ma (kgm/s2)
Gravity
 Einstein ... space-time
 But, do we REALLY understand gravity?