Download Astronomy 101 -- Worksheet #3 PLANETARY POSITIONS AND

Astronomy 101 -- Worksheet #3
PLANETARY POSITIONS AND HISTORY OF ASTRONOMY
1) The planets appear to move among the stars from night to night because of the
_____________________________________________________________.
2) The planets are always found in a particular part of the sky near the _____________, called the
________________.
3) The planets _____________ and _____________ are always found close to the Sun in the sky, and are
sometimes called morning stars or evening stars. Because these planets are close to the Sun, they are
never visible at _______________.
4) The planets _____________, _____________, and _____________ can be found anywhere along the
ecliptic, and are therefore visible at any time of day or night.
5) The bright planet which can be visible in the western sky for up to 3 hours after sunset, and at other
times in the eastern sky for up to 3 hours before sunrise is ___________________.
6) The sky is generally divided in 88 regions, or _______________, which are the apparent configurations of the stars we see in the sky. Many of the ______________ are of Greek origin, and bear names
which are Latin translations of the Greek names.
7) There are ____________ constellations seen in the direction of the _______________, the Sun’s path
on the sky, and as a group these are called the constellations of the _______________. The word
_______________ itself means "zone of the animals".
8) The Ancient Greeks (∼500-300 B.C.) believed that the world was made of 4 elements:
_____________, _____________, _____________, and _____________.
9) The Ancient Greeks believed in the _____________ model of the Solar System. In this model, the
_____________ is at rest, the _____________ is at the center, and the _____________, _____________,
and _____________ all orbit the _____________ on orbits which have the shape of
_________________________.
10) Ptolemy (∼100-200 A.D.) was able to explain the presence of non-uniform motions of the planets by
adding _____________ to the planetary orbits. The resulting model of the Solar System, also called the
_____________ model, was able to predict accurate positions of the planets for 1400 years.
11) During the Renaissance, the Polish astronomer Niklas Copernicus (1473-1543) proposed a new model of the Solar System, also called the ________________ model. In this new model, the __________ is
at the center, and the _____________ and _____________ orbit the _____________ on orbits which have
the shape of _____________.
12) As originally proposed by Copernicus, with circular orbits for the planets, the _____________ model
was NO MORE ACCURATE than the older _____________ model. It was the observations made 100
years later by Galileo that proved which one of the models was correct.
-213) Among the important contributions of the astronomer Tycho Brahe (1546-1601) to our understanding
of the Solar System were his extensive measurements of _________________________.
14) Tycho’s young assistant, Johannes Kepler (1571-1630), used 20 years worth of measurements in order to determine the _______________________________. From this analysis, Kepler was able to show
that the positions and motions of the planets can be described by 3 general Laws of Planetary Motion.
15) Kepler’s 1st Law states that the _____________ orbit the _____________ on orbits which have the
shape of ____________________.
16) Kepler’s 2nd Law states that equal _____________ are swept out in equal _____________. In other
words, a planet moves fastest in its orbit when it is _______________________________________.
17) Kepler’s 3rd Law states that the _______________________ of a planet is related to its
______________________________. This implies that planets which are ____________________ (closer to/farther from) the _____________, on average actually move SLOWER in their orbits.
18) Kepler’s version of the ____________________ model was simple and was able to predict accurate
positions of the planets. This model could also easily explain the apparent backward motion of planets,
also called _________________________.
19) The first scientist to use a telescope to observe the sky was _________________________. With the
telescope, he reported seeing _____________ on the Sun, ____________________________ on the
Moon, _____________ in the Milky Way, ________________ orbiting Jupiter, and
____________________ of Venus.
20) From his observations of the ___________________________________, Galileo found indisputable
evidence in favor of the ____________________ model of the Solar System.
21) From his experiments in physics, Isaac Newton (1643-1727) developed 3 Laws of Motion. Newton’s
1st Law states that an object at rest ______________________________, and an object in motion
______________________________, unless ______________________________. Newton’s 2nd Law
states that the acceleration an object feels depends on the ________________ divided by the
____________________. Newton’s 3rd Law states that for every action there is ____________________
_______________________________.
22) Based on Kepler’s Laws, the Moon’s orbit, and falling objects on the Earth, Newton formulated the
Law of ________________________________________, which explains the motions of the Moon, planets, stars, and galaxies.
23) The force of gravity between two objects depends on the _______________ of each of the objects,
and the _____________________________. If the distance between two objects is tripled, the force of
gravity between them becomes ______________.