Week 4 Observations: Lunar Phases and Period Lab

Astronomy 25 Section 60530

February 8, 2024

Allen Schiano, Lecturer and Richard Faulkner, Lab Technician

Purpose(s) of Lab:

To study the phases and orbit of the Moon by noting the visual phases of the Moon during THREE ‘Lunation’ periods of the Moon. Then analyzing that data to determine the Period of the Moon’s Orbit as seen from Earth.

Apparatus used in the Lab:

Your eyes

A ‘log book’ of sketches of the moon and date and times of the observations

A calculator to compute the Period of the Moon’s Orbit

Background:

The moon goes through a series of ‘phases’ over time as seen from the Earth. The shape of the ‘lit’ side (lighted by the Sun) varies with time. Sketching the appearance of the Moon with your eyes from the Earth should allow you to determine the length of the Lunar ‘Month’.

This Lab will take ALL SEMESTER TO COMPLETE. As such, you can divide the work (taking daily observations) among the members of your ‘group’. If you wish, you can complete the observations individually.

To compute a reasonably accurate log and measurement of the Lunar Month, you will need to observe the moon for 3 approximately TWO WEEK periods. THERE IS NO NEED TO OBSERVE THE MOON DURING THE “VERY LATE NIGHT” PHASES.

Procedure:

1) Determine a schedule with your group about who will observe and sketch the Moon of the ‘Observing Period’. Divide up the work and note who took the data on each day. You can try to observe the Moon during the day – enough to see the phase and sketch it – as well as at night.

2) Observe the Moon and sketch it in a ‘log book’. NOTE THE DAY AND TIME OF DAY TO THE HOUR.

3) At then end of the last ‘Observing Period’, analyze your data to determine the Lunar Month (see below). Us the data to estimate your uncertainty from the data as well.

Observing Periods (someone has been keeping track of these for about 100 years!):

Lunation 1251 : February 12 to February 26

Lunation 1252 : March 13 to March 27

Lunation 1253 : April 11 to April 25

Data:

Your data will consist of the sketches and the dates and time (to one hour accuracy!!) placed into a ‘Lunar Log’. I include a typical page below to include copies of in the Lab Report as your data.

Analysis:

The goal of the Analysis is to compute the Lunar Month. The Lunar Month is defined as the time between successive SAME phases of the Moon. This is somewhat difficult to measure with the eye only. The best times are near the ‘Half Moons’ phases. You can also do this between ‘Full Moons’ but it is trickier to determine the exact date and time of a Full Moon.

As such, it is critical that you observe the Moon very close to Half Moon phase each of the three months.

Counting Days:

We want to count the days starting from Day 0 on February 9th. So, February 9 would be Day 0. February 10 would be Day 1. Keep this date on your log starting on February 9.

Counting Decimal Days from the Time:

To determine the day accurate to an hour, note the time of day when you think each phase has occurred. Compute a digital day by dividing the hour (in ‘military time’ format) by 24. Or

For AM hours : Time in hours/24 = decimal day

For PM hours: (Time in hours+12)/24 = decimal day

Add decimal day to counting day. For example, let’s say you saw the moon at February 18th at 5 PM.

1) February 18th is the 9th day since February 9th would be Day 0 (you can subtract dates for the first month ONLY)

2) 5 PM is in the afternoon, so, to get the decimal day, we have (5+12)/24 = 0.77. You can round this to 0.8

3) Add the two parts to the day – the day (9) + decimal part of the day (0.8) =9.8

4) That would be the decimal date for your observation.

5) In subsequent months, use a calendar to count the number of days since February 9th! Don’t use any other day as the starting day!

Analyze your data for two critical phases: A) Half Moons and B) Full Moons. Write down our results as

Half Moons:

Lunation 1251 Half Moon Phase time (decimal days): _______________

Lunation 1252 Half Moon Phase time (decimal days): _______________

Lunation 1253 Half Moon Phase time (decimal days): _______________

Full Moons:

Lunation 1251 Full Moon Phase time (decimal days): _______________

Lunation 1252 Full Moon Phase time (decimal days): _______________

Lunation 1253 Full Moon Phase time (decimal days): _______________

From this data, subtract consecutive phase times to get Lunar Month Estimates:

Half Moon Months:

Lunation 1252 – Lunation 1251 = ___________________________

Lunation 1253 – Lunation 1252 = ___________________________

Average off Half Month Lunar Months = _____________________ (your best measurement of the Lunar Month!)

Full Moon Months:

Lunation 1252 – Lunation 1251 = ___________________________

Lunation 1253 – Lunation 1252 = ___________________________

Lastly, conclude this experiment, this by averaging all the Lunar Months, and estimating the Uncertainty as the longest month – the shortest month and then divide by two

Lunar Month = ______________________ +/- the Uncertainty = ___________________

Sample Lunar Log Page (create as you prefer, but include all these parts)

Name of Person Observing_____________________

Day_________________________

Days Since February 9th________________________

Time of Day (include AM /PM)_________________

Decimal Day _____________________

Decimal Days since February 9th________________

Sketch the Moon – making sure the shape is carefully drawn and you can add ‘features’

___________________________________________________________________________________________ Name of Person Observing_____________________

Day_________________________

Days Since February 9th________________________

Time of Day (include AM /PM)_________________

Decimal Day _____________________

Decimal Days since February 9th________________

Sketch the Moon – making sure the shape is carefully drawn and you can add ‘features’

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