Astronomy 4

Night Exercises: Supplementary Questions

I. Lunar Motions

    A. Lunar Phases

         i. The Synodic Period of the Moon

1. From your observational data, you can determine how long it takes for phases of the moon to repeat themselves (this is called the synodic period of the moon).

    a. What is your estimated period for the moon to repeat its phases? For example, over the 3 months of the semester, what is the average time it takes for the moon to go from full moon to full moon, or first quarter to first quarter?

Derived Synodic Period:

 

    b. This period is called the "synodic period". What is the accepted synodic period of the moon?  You will have to look this up in a book, or on the Web!

Accepted Synodic Period:

 

    c. How does your derived value compare with the accepted synodic period of the moon?  In other words, what was the error in your derived synodic period?

Error In Derived Synodic Period:

 

2. Is your derived synodic period within the errors you expect?

    a. How accurately do you think you can establish the phase of the moon? Express your "uncertainty" in days, or fractions of days.

Expected Uncertainty in Lunar Phase:

 

    b. Is the error you derived for the synodic period (box 1c)   consistent with your derived uncertainty for deriving the lunar phase?  In other words, given your estimated error in lunar phase determination, is your derived synodic period consistent with the accepted synodic period? Why or why not?

3. Describe briefly  how you might improve upon your derived synodic period for the moon.  In other words, what contributed (e.g., weather) to your "uncertainty", or error, in establishing the synodic period, and how might you minimize these factors in future "experiments"?

ii. Relation Of The Sun And Moon Positions With Respect To Phases

1. The full moon

    a. On what date/dates did you observe the moon at/near full phase?

Date(s):

 

    b. When you saw the moon near full phase, how far (in angular units) was the Sun?

Angular Separation (degrees):

 

    c. Was the Sun east or west of the moon?

Direction of the Sun:

 

    d. If you were to have observed the full moon at sunrise, where would it be located in the sky?  Why?

2. The first quarter moon

    a. On what date/dates did you observe the moon at/near the first quarter phase?

Date(s):

 

    b. When you saw the moon near the first quarter phase, how far (in angular units) was the Sun?

Angular Separation (degrees):

 

    c. Was the Sun east or west of the moon?

Direction of the Sun:

 

    d. At sunrise, where would the first quarter moon be located in the sky?  Why?

3. The third quarter moon. If you were to have observed the third quarter moon at sunrise, where would it be located in the sky?  Why?

4. a. What was the earliest lunar phase (after new moon) that you were able to observe?

Earliest phase:                                                                                

 

    b. On what date(s) did you observe this phase?

Date:                                                                                

 

    c. When you observed this phase, how far was the Sun from the Moon in angular units?

Angular Separation (degrees):

 

    d. Was the Sun east or west of the moon?

Direction of the Sun:

 

d. Based on these results, and using the fact that the moon moves eastward across the sky at a rate of about 13 degrees per day, on what date(s) would the moon have been new?

Date(s) of New Moon::

 

5. Easter Sunday falls on the first Sunday after the first full moon after the vernal equinox. Describe how your observations of the moon in March and April agree or disagree with this definition: NOTE THIS QUESTION ONLY APPLIES FOR THOSE TAKING THE CLASS IN THE SPRING SEMESTER!

B. The Sidereal Period of the Moon

1. Based on your plots showing the position of the moon with respect to the background stars, along with the dates/times of the observations you plotted, you should be able to estimate how long it takes for the moon to repeat its position with respect to the background stars.

    a. What is your estimated period for the moon to repeat is position with respect to the background stars?

Period (days):

 

    b. This period is called the "sidereal period". What is the accepted sidereal period of the moon? Accepted

Accepted Sidereal Period (days):

 

    c. How does your derived value compare with the accepted sidereal period of the moon?

Comparison:

 

2. How accurately do you think you can plot the position of the moon with respect to the background stars when the moon is in the following phases.  Express your answer in degrees. In other words, what is your estimate for the uncertainty in your measurements of the moon’s position?

a. a thin crescent?________________________

b. a quarter moon?_______________________

c. near full phase?________________________

3. What other sources of uncertainty contribute to your estimate of the sidereal period of the moon?

4. Among ancient cultures (e.g., the Inca, the Maya), there is little evidence that the sidereal period of the moon was measured. Based on your above results, can you suggest one reason that this might have been?

5. Describe in some detail a possible way that you might improve upon your estimate of the sidereal period of the moon.

II. Stellar Motions

1. a. How many days elapsed between your first observation of the constellations, at the same time after sunset, and your last?

Number of Days:

 

    b. Based on your observations of the changing appearance of the constellations after sunset, estimate how far the sun moved in the sky over the time period in part a. To do this you will need to estimate how many degrees the constellations moved during this time period.  To do so, figure out which constellation at the end of the time period replaced the constellation that was visible at the beginning of the time period.  Then look on a star chart to establish how many degrees separate the constellations.  Since the Sun moves with respect to the constellations, this will tell you how far the sun moved in the sky over the time period!  Be sure you understand what you are doing here!

Degrees The Sun Moved Relative To The Sun:

 

    c. Given the elapsed time period in part a, is your estimate in part b for the angular motion of the sun during this period what you expect (within your observational errors)? Why or why not? (that is, if not, discuss what sort of errors could lead to "unexpected" answers).

2. a. In the night observing exercises, you recorded the altitude of Polaris. Based on this result, what is the latitude of Sacramento? How well does this agree with the expected value?

Derived Latitude of Sacramento:

 

Accepted Latitude of Sacramento:

 

b. Discuss why your observed latitude in a. agrees or does not agree with the expected value.

III. Solar Motions

1. a. How many days elapsed between your first solar observation and your last?

Elapsed Number of Days:

 

    b. Approximately how far, in azimuth (along the horizon), did the sun move over this period?

Change in Azimuth:

 

    c. On average, how many degrees per day along the horizon did the sun move over this period?

Horizon Motion in Degrees/Day:

 

    d. From your data, can you say if the speed of the sun along the horizon varied over this period? If so, approximately when did it appear to move the fastest?

2. Describe in some detail how reliably  your observations suggest that the equinoxes could be established.

IV. Planetary Motions - 10% Bonus for the ENITRE Night Exercises!

1. Based on your observations of Venus, discuss why it played such a prominent role (including its association with gods) in the lives of many indigenous cultures in the Americas. Use as many examples of its appearance in religion/folklore as possible (this will require some research!)