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Astronomy Notes.docx

59 Pages

Astrophysical & Planetary Sciences
Course Code
ASTR 3300

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Astronomy: Life in the Universe 09/11/2013
Extraterrestrial life – life beyond earth
Astrobiology – combination of astronomy (study of the universe) and biology (study of life)
Focuses on:
Studying the conditions conductive to the origin and ongoing existence of life.
Looking for such conditions on other planets in our solar system + around other stars.
Looking for the actual occurrence of life elsewhere.
Microbes – single celled organisms too small to see with naked yee. Stretch the extreme living
conditions on Earth, first life forms on earth and are anywhere life exists on earth.
Scientific model – Conceptual representation whose purpose is to explain and predict observed
Theory – When a powerful yet simple model makes predictions that survive repeated and varied testing.
Cannot prove theories are correct.
Orbital period – time it takes for an object to complete one orbit.
Apparent retrograde motion – when planets reverse direction and move westward relative to the
stars opposed to eastward, usually happens from a few weeks to a few months.
Stellar parallax – annual shifts in star position.
Occam’s Razor – The idea that scientists should prefer the simpler of two models that agree equally
well with observations.
Atomists – Believed that our world formed among an infinite number of indivisible atoms and this infinity
implied the existence of other worlds.
Aristotelians – Believed that all Earth must have fallen to the center of the universe, which rationalized
the belief in a geocentric universe and the belief that the heavens were fundamentally different from Earth,
which implied that earth must be unique in which case no other worlds or other life could exist.
Geocentric model (Ptomlemy) – (Earth Centered) A spherical Earth at the center of a great
celestial sphere.
Heliocentric (Copernicus) – Sun in the center.
Pillars of Science: (ways to learn about the world)
Hallmarks of science:
Modern science seeks explanations for observed phenomena that rely solely on natural causes.
Science progresses through the creation and testing of models of nature that explain the observations as
simply as possible.
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.
The Big Three:
The right chemical elements with which to build living organisms.
A source of energy to fuel metabolism.
A liquid substrate to enable chemical reactions (usually water)
Kepler’s laws:
Each planets orbit is an ellipse with the sun at one focus in the center. A planets distance form the sun
Perihelion – closest to the sun.
Aphelion – farthest from the sun.
Semi-major axis – planets average distance from the sun.
As a planet moves around its orbit it sweeps out equal areas in equal times.
A planet moves faster when near perihelion (closer) and slower when near aphelion (farther).
More distant planets orbit the sun at slower average speeds.
P2 = a3. P = planets orbital period in years. A = semi-major axis (average distance) in astronomical units.
Newton’s laws:
An object in motion tends to stay in motion unless acted upon by a force.
Force = Mass x Acceleration. Or Acceleration = Force/Mass.
When an object exerts a force on another object that object exerts the same force back, but in the opposite
Angular Momentum - The total amount of circling motion of an object or set of objects must be
Astronomy: Life in the Universe 09/11/2013
Week 2: Homework #1 Due Tues. Sept. 10

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