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ASTR 380 Study Guide - Comprehensive Final Exam Guide - Astrobiology, Earth, Mars


Department
Astronomy
Course Code
ASTR 380
Professor
Hudson
Study Guide
Final

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ASTR 380

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Astrobiology: Historical Background (January 30th, 2018)
It has long been known that…
o …the Sun, the Moon, the planets, and the stars move about the sky.
o …the Earth is spherical.
o …the Earth’s size is finite.
Eratosthenes’s Experiment
o On the first day of summer, a stick in the ground in Syene casts no shadow, but
one in Alexandria casts one at an angle of about 7.5 degrees.
o There is a distance of about 800 kilometers between the two cities.
o Since the shadow is cast at an angle of 7.5 degrees, this means that the angle the
two sticks make if extended to the center of the Earth is 7.5 degrees.
o Knowing that a circle has 360 degrees, Eratosthenes found that the earth is
approximately 39,000 kilometers.
The Evolving Model of the Universe
o Claudius Ptolemy (c. 150), a Greco-Egyptian astronomer, explained the
“wandering” of planets using epicycles, which is an orbital path that a planet
follows in addition to its orbital path (the deferent) around the Earth.
o Nicholas Copernicus (1473 1543), a Polish astronomer, formulated a
heliocentric model based on his observations.
His theory was published near his death in order to escape the Inquisition.
o Tycho Brahe (1546 1601), a Danish astronomer, along with his Austrian partner
Johannes Kepler (1571 1630) refined the heliocentric model.
Brahe observed a supernova and disproved the theory that comets come
from within the Earth’s atmosphere from his private observatory in
Denmark.
Kepler formulated three laws of planetary motion.
First Law: Planets orbit the Sun in elliptical orbits.
Second Law: Orbital speed is inversely proportional to distance
from the Sun. (i.e. planets closer to the Sun orbit the Sun more
quickly than farther out planets)
Third Law:
 
o a is the average distance between the body and the Sun
o P is the orbital period of the body
o The ratio between the average distance cubed and the
orbital period squared is a constant for all planets within a
given solar system (assuming a unary star system).
o Galileo Galilei (1564 1642), an Italian physicist, studied motion.
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His book on his telescope observations was written in Italian (not Latin as
was conventional at the time) and became a sensation.
Using his telescope, he found…
…that the Moon is not perfectly smooth, but rather has a cratered
surface.
…that Jupiter has satellites (Io, Europa, Ganymede, Callisto) and
observed their motions, the first such motions of objects orbiting
an central body other than the Sun.
…that the Milky Way is composed of stars.
…that Venus has phases similar to the Moon.
…sunspots.
The Church forced him to renounce the heliocentric model on threat of
excommunication.
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