Assignment 1
Due date: October 5, 2009
1)
a)
One common length unit in astronomy is astronomical unit (A.U.). How long is 1
A.U. in terms of meters?
b)
Look up the mean diameter of the Moon and the mean EarthMoon distance.
c)
By using the above data, calculate the mean angular size of the Moon.
d)
During total solar eclipses, the angular size of the Moon is just large enough to
cover the Sun. Estimate the diameter of the Sun.
2)
If the direction of rotation of the Earth was reversed and the direction of
revolution remained the same, would the sidereal day be longer than the solar
day?
3)
Is Venus a morning star or evening star in these two weeks (end of September)?
How about Mercury? (This is Question 4 of Assignment 1 in 20072008.)
4)
In the Chinese Agricultural Calendar, a month is defined by the synodic month
and a year consists of integral number of month. Hence, in some years, there are
thirteen, instead of usual twelve, months. That extra month is called leap month.
Given that a year has 365.24 solar days and a synodic month has 29.53 solar days.
How many leap months are there in 19 years?
5)
Let's assume for simplicity that the orbital plane of Mars is the same as the
orbital plane of Earth, and the angle between its rotational axis and revolution
axis is 25°. For observers on Mars, is their north celestial pole same as ours? Is
their ecliptic same as ours? Are their zodiac same as ours? Can they observe
retrograde motion of the Earth?
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View Full DocumentSolutions of Assignment 1
Due date: October 5, 2009
1)
a)
1 A.U. = 1.5x10
11
m.
b)
The diameter of the Moon is about 3.5x10
6
m, and the mean EarthMoon
distance is about 3.9x10
8
m.
c)
The mean angular size of the Moon is
tan
1
(3.5x10
6
/ 3.9x10
8
) = 0.51°
d)
The Sun has about the same angular size with the Moon. Hence, the diameter of
the Sun is about
(3.5x10
6
/ 3.9x10
8
) x 1.5x10
11
= 1.3x10
9
m
2)
The sidereal day would be longer than a solar day. This is because if the directions
of rotation and revolution were not the same, the advancing of the Earth in its
orbit would take it to a position that it did not need to rotate a full turn to face
the Sun again. This led to a shorter solar day. (Recall that in the actual SunEarth
system, the Earth has to rotate a bit more than a full turn to face the Sun again.)
3)
Looking up some websites or astronomical almanac, one will find that both Venus
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 Spring '10
 Prof
 Ecliptic, Angular Size

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