Description: In this lab you will observe the changing phase of the moon nightly for two weeks.
Timing Options: Choose one of the three options below. You will need to observe at the exact same time (+/- 10 minutes) each night, although that time may be +/- ~30 minutes from the times listed below. For example, you can observe the moon at 8:30 instead of 9:00, but all of your observations must them be within ~10 minutes of 8:30.
(1) Observe the moon at 9pm daily beginning just after the new moon (1 or 2 days) and ending just after the full moon
(2) Observe the moon at midnight daily beginning at the first quarter and ending at third quarter.
(3) Observe the moon at 5am daily beginning just before the full moon and ending around the new moon.
Resources:
Materials needed: Astrolabe, large piece of sketch paper, compass, camera (optional)
Instructions:
(1) Find a place to do your observations where the horizon is relatively unobscured toward the south.
(2) Sketch that horizon along the bottom of a large piece of paper all the way from East to West. Mark East, West and South on your chart using a compass and divide that horizon into 10 degree segments (East to West is 180 degrees, so there should be 18 of these). A fist held at arms length takes up about ten degrees, so you can use that to check the rough locations you’ve sketched on your true horizon. Number these ten degree increments starting at zero on the western horizon and ending at 180 on the eastern horizon (due South should therefore be 90, halfway in between).
**Take the time to make this sketch carefully. You only have to do it once and doing it carefully the first time will save you a lot of frustration later!
(3) Beginning at the moon phase and time you chose above, record on the same sketch the following things each day for the next 14 days:
- Sketch the moon as it appears to you in size, location and orientation (i.e. which way does the crescent face?) on your sketch. Make sure to distinguish between the light and dark portions by shading or using color.
- Record the date and time next to the moon you’ve drawn
- Record the nearest point on the horizon to the moon (straight down from the moon) and mark that location on the horizon with the date.
- Use your astrolabe to calculate the altitude of the moon from the nearest point on the horizon (this should be a number between 0 and 90 degrees each time) and record that as well. You may wish to use the “fist and finger method” to estimate first and use that number to make sure you’re in the right ballpark with your astrolabe.
- Use a clear ruler held at arm’s length or the fist and finger method to record the size of the moon (note: even in it’s crescent phase you can still make out the outline of the entire moon).
- If you don’t see the moon or it’s too cloudy to see it, make a note of that. You have to have seen the moon on at least 10 of the 14 days for this project.
Note: You may also choose to photograph the moon each night. This can be a good backup to tweak your sketch when you’ve collected all of your data and also a good visual aid for your presentation. Make sure to include the horizon and the moon in at least one picture each night (zoomed all the way out) so that you have a good reference point.
Data: Your final products will be:
(1) A sketch or composite photograph showing the moon moving in the sky over the course of two weeks.
(2) A data table showing the time, direction, altitude and phase of the moon each day you observed it.
Questions to Address in Your Poster’s Data Analysis Section:
(1) How many degrees did the moon move along the horizon (east/west) each day? Describe the range and the average.
(2) How many degrees did the moon move vertically (in altitude as measure by your astrolabe) each day? Describe the range and the average.
(3) How many total degrees did the moon move each day? Describe the range and the average.
(4) Using your moon size measurements, calculate the percentage change in the size of the moon over the course of your observations. There are several correct ways to do this. See me if you have trouble.
(5) In your own words, describe why the location of the moon changes in the sky as viewed at the same time over the course of its monthly cycle.
(6) Which direction do the “horns” of the moon point and why?
(7) Why was this project assigned for a two week period and not for an entire monthly cycle of the moon?