AST 3018
HOMEWORK #2
KEY
1. Your longitude is 66 degrees west.
a. What time zone are you in? - Atlantic Standard Time (AST)
b. What time does the mean Sun transit? 12:24 PM AST
2. The full Moon will set in three hours. What time is it? 3:00 AM
3. It is 6:00 PM. The Moon will rise in three hours. What is the phase of the Moon? –
Waning Gibbous
4. It is 9:00 PM, August 21. The Moon will transit in three hours.
a. What is the phase of the Moon? - Full
b. What is the right ascension of the Moon? 22 Hours
5. I observe a lunar eclipse to occur at sunset on September 21.
a. What is the phase of the Moon? Full
b. What is the Moon’s right ascension? 0 Hours
c. What is the Moon’s declination? 0 Degrees
d. What is the Moon’s hour angle? 18 Hours
e. What is the Moon’s azimuth? 90 Degrees
f. What is the Moon’s zenith angle? 90 Degrees
g. What is the Sidereal Time? 18 Hours
6. A given object has a right ascension of 14 hours 15 minutes and an hour angle of
16 hours 50 minutes. What is the sidereal time? 7 Hours 5 Minutes
7. Describe the daily, monthly and annual motion and appearance of the Moon for an
observer at the North Pole.
Daily: Provided the Moon is visible at all it would travel on a diurnal circle
counterclockwise around Polaris parallel to the horizon. It would be visible during the
entire day.
Monthly: The Moon would be visible, on the average, only half of the month as its
monthly path carries it along (or very near to) the ecliptic. It would appear to rise up to
an elevation of 23.5 degrees (± 5 degrees) for a week then recede for a week then
disappear for two weeks.
Annual: Between March 21 and September 21 the Sun would be in the sky. Between
September 21 and March 21 the Sun would be down. If the Moon can be seen it will
have to be east of the Sun, therefore it will be between new and full phase (waxing
phases) between March 21 and September 21 if it is visible. If it cannot be seen during
this period it must be between full and new phase (waning phases). It will be just the
opposite for the dates when the Sun is below the horizon.
8. Would a lunar eclipse occurring in January be visible from the South Pole? Why or why
not? Would this eclipse be visible from every location on the every location on the
Earth’s equator? – It would not be visible. In January the Sun a southern declination.
Lunar eclipses occur at full Moon. That would place the Moon at a northern declination
hence below the horizon at the South Pole. It would not be visible for every observer on
the Earth’s equator as the Moon must be above an observer’s horizon in order for one to
see it. The Moon is up for only half of the observers on the Earth’s equator.
9. Does each of the Earth’s poles enjoy the same amount of daylight during the year? If not
which of them has the most daylight? Why? – No. The North Pole enjoys more daylight.
The Earth comes to perigee in early January and apogee in early July. Consequently the
time between 9/21 and 3/21 is shorter than that between 3/21 and 9/21 because the Sun
moves through the first interval faster than the second. The difference is about 4 days.
10. It is 3:00 PM July 31 EST. What time is it in the local time zone at 115 degrees east
longitude? What is the longitude at the time zone center? 4:20, AM, 120 Degrees East
11. What two phenomena contribute to the analemma? – The tilt of the Earth’s pole (ecliptic)
and fact that the Earth’s orbit is elliptical