Topic 1

Question 1

What is the Ecliptic

Answer 1

-The path of the sun on the celestial sphere

Question 2

Sky at the equator:

Answer 2

Turns perpendicular to the floor

Question 3

Sky at the north/south pole

Answer 3

Turns parallel to the floor

Question 4

Celestial equator

Answer 4

separates N and S hemispheres of celestial sphere

extension of the Earth’s equator into space

Question 5

Hipparchus:

Answer 5

The greatest astronomy observer of Antiquity:
•
Determined that the Moon’s average distance is
29.5 times Earth’s diameter (modern value is 30)
•
Measured length of the year to ~6min accuracy.
•
Created a catalog with 850 stars and classified
them based on their brightness. This is used as
the basis for the modern magnitude scale
•
Most important achievement: He discovered the
precession of Earth.

Question 6

Aristarchus of Samos

Answer 6

Calculated the distance to the Sun

The distance to the Moon, required to find an answer, was calculated by
Hipparchus

Question 7

Aristotle

Answer 7

Heliocentric vs. Geocentric : absence of stellar parallax

Question 8

Geocentric model:

Answer 8

Ptolemy
(Alexandria, ~140A.
•
Explain Retrograde motion
•
Orbits must be circles
•
Speed of planets is constant

Ptolemy’s Solution:
–
Epicycles (circle within
–
Center of the epicycle follows
larger circle called deferent
–
Earth is near the center of the
deferent

Question 9

Heliocentric model:

Answer 9

Nicolaus
Copernicus (1473 1543)
•
Heliocentric model: solves retrograde motion
problem in an elegant way.
•
Able to determine the scale of the solar system.

Question 10

Superior planets:

Answer 10

Further from the sun than the earth

Angle of elongation CAN reach 90 degrees

Question 11

Inferior planet:

Answer 11

Closer to the sun than the earth

Angle of elongation always less than 90 Degrees

Question 12

Sidereal period:

Answer 12

Time for one revolution, impossible to measure directly

Question 13

Synodic period:

Answer 13

Apparent period of revolution, relative to the earth - measurable.

Question 14

Interlude: Tycho Brahe

Answer 14

Last great naked eye astronomer
•
Measured positions of planets and stars with accuracy of the order of
1’ of arc
•
Could not make a model that would agree with his accurate
observations (he tried a hybrid geo heliocentric model)
•
He hired a young German mathematician to help design a new
model: Johannes Kepler

Question 15

1.3.2 Johannes

Kepler

Answer 15

Three
laws of planetary motion ( still valid today
Terminology
New key words
•
Semi major axis
•
Semi minor axis
•
Focus (and focal
•
Eccentricity
•
Periapsis (also perigee and perihelion) -> r1 
•
Apoapsis (also apogee and aphelion) -> r2
•
Semilatus rectum :

Question 16

1.3.3 Galileo Galilei

Answer 16

•
Copernicus Re introduced the heliocentric model
and did some math
•
Kepler refined the model and did some more math
•
Galileo brought empirical evidence to prove it
•
Five key observations made by Galileo sealed the
fate of the geocentric model.

Question 17

Galileo’s five observations:

Answer 17

Moons of Jupiter, phases of Venus, Surface of the moon, Sunspots, the milky way.