Solutions to Homework 02
Please answer at least 4 of the following 5 questions correctly for full
credit:
Question 1
Two conditions need to be met simultaneously for an eclipse to occur. One is
that the Moon be either new or full. What is the other condition?
Answer:
The plane in which the Moon orbits around the Earth and the plane in which the
Earth orbits around the Sun are inclined with respect to each other. There is
exactly one line where the two planes intersect. For the Moon to be between
the Earth and the Sun (solar eclipse) we have to have a New Moon at the same
time that this line from the two intersecting planes aligns with the direction
from the Earth to the Sun. For a lunar eclipse we have to have a full moon at
the same time that the line from the two intersecting planes aligns with the
Earth-Sun direction.
Question 2
Can you have a lunar eclipse on a New Moon?
Answer:
No. For a New Moon to occur the Moon has to be near the direction connecting
the Sun and the Earth, which is one of the two conditions that have to be met
for a solar eclipse to occur. The Moon's shadow would fall onto Earth to give
rise to a solar eclipse if a New Moon occurs when the line derived from the
two planes descibed in the answer to Question one aligns with the line
connecting the Earth and the Sun. Lunar eclipses are associated with Full
Moons.
Question 3
Spheres and circles were the perfect forms of old.
Copernicus made a great scientific advance by re-introducing the
heliocentric model of our solar system, but was
still unable to think of celestial motion as anything but circular.
Give the names of the two types of circles used to explain the observed
planetary orbits
in the Copernican as well as Ptolemaic model of the solar system.
Answer:
The two types of circles used in the Copernican and Ptolemaic model of the
solar system are the Deferent and the Epicycle.
Question 4
How bright a planet appears in the night sky is coupled to the relative
position of the planet and earth.
What is the most important factor that determines if Jupiter appears brighter
or dimmer in the night sky?
Answer:
The so-called apparent brightness of Jupiter is controlled mostly by by its
distance from Earth. For the inferior planets phases also play an important
role, but for the superior Jupiter that is not an important effect. Remember
the video clip I showed in class about Jupiter and Saturn going into retrograde
motion: We watched the brightness change as the two planets came closer to
Earth and then receded again to resume their normal prograde motion across the
night sky.
Question 5
Which direction does a comet's tail point? When you answer this question,
please remember that along any axis there always are two different orientations
that a direction aligned with the axis can have. Be specific about the
orientation also when you describe the direction. Depending on what the axis
is, is it pointing outward or
inward, forward or backward, left or right, up or down?
Answer:
A comet's tail points away from the Sun along the direction connecting the
comet to the sun. The tail is formed by the so-called solar wind as it blows
material evaporating from the comet away from the sun.
The deadline for submitting solutions to this homework has passed.
Last modified: Thu Jan 24 20:28:39 MST 2008