Download Physics 121, Problem Set #3 Solutions Review Questions (Chapter

Physics 121, Problem Set #3 Solutions
Review Questions (Chapter 3)
2. If the Earth did not rotate, could we define the ecliptic? Why or why
not?
If we mean Earth does not turn on its axis with respect to the stars,
then defining an ecliptic would be possible but it would mean using
observations from many different locations on Earth. In this case
defining latitude could get a little tricky since there would be no pole
star. If we mean that Earth does not rotate with respect to the sun (i.e.
Earth being in synchronous rotation with the sun), it would be
possible, but again would require coordinated observations between
the lit side and dark side. Celestial poles and an equator could be
defined under these circumstances.
6. What phase would Earth be in if you where on the moon when the
moon was full? at first quarter? at waning crescent?
new, third quarter, waxing crescent
9. Why isn’t there an eclipse at every new moon and at every full moon?
Eclipses occur only when the sun, Earth and moon are directly in line
with each other. The moon's orbit is inclined about 5° with respect to
the ecliptic so that when the moon is either new or full it may be as
much as 5° north or south of the ecliptic. For an eclipse to occur then,
the moon must be either full or new AND be very near the ecliptic.
Usually when the moon is new or full it is north or south of the ecliptic
and an eclipse does not occur.
Problems (Chapter 3)
2. Identify the phases of the moon if on march 21 the moon where
located at (a) the vernal equinox, (b) the autumnal equinox (c)
summer solstice (d) winter solstice?
On March 21st the sun is in the direction of the vernal equinox.
looking on page 28 you can find the phase of the moon: a) new, b) full, c)
first quarter, d) third quarter
summer
solstice
autumnal
equinox
vernal
equinox
winter
3. Identify the phases ofsolstice
the moon if at sunset the moon where (a) near
the eastern horizon, (b) high in the south, (c) in the southeast, (d) in
the southwest
For this we need to look at the diagram on the bottom of page 28.
1st quarter
Waxing crescent
South
fullWaxing
moon gibbous
East
West
new moon
a) full, b) first quarter, c) waxing gibbous, d) waxing crescent
6. Phobos one of the moons of mars is 20 km in diameter and orbits
5982 km above the surface of the planet. what is the angular
diameter of Phobos as seen from Mars? (Hint: See by the numbers
3-1.)
Here we will use the small angle formula:
angular diameter
=
206,265
ad
linear diameter
distance
20 km
=
206265
5982 km
ad = 690 secounds of arc
690 arc seconds or 11 arc minutes or one-fifth of a degree.