Phases of the Moon and Planets Lab

Caleb W. Skocy

AST 115 Honors

3 February 2016

Lab Report #1

Lunar and Planetary Phases

In this lab, we examined the phases of the Moon, its position in the sky, and its rotation.  We learned that there are several things we can infer from observing the Moon’s phases, position, and rotation; and these include the Moon’s position relative to the Earth and Sun, the time, and whether there really is a “dark” side of the Moon.  We applied our observations of the Moon to other planets in our solar system and discovered that the phases of the other planets could tell us some very useful information about Earth’s position in our solar system.  To do all this, we separated our lab into four parts: 1) Phases of the Moon, 2) Where is the Moon in the sky?, 3) The Moon’s rotation, and 4) Phases of the planets.

Part 1: Phases of the Moon

The Moon goes through eight phases.  These are (in order): New, Waxing Crescent, 1st Quarter, Waxing Gibbous, Full, Waning Gibbous, 3rd Quarter, and Waning Crescent.  Waxing means that the Moon is becoming more illuminated and heading towards a Full Moon; inversely, a Waning Moon is becoming less illuminated, working towards a New Moon.  The Moon is a Crescent Moon when it is less than half illuminated, whereas the Gibbous Moon is more than halfway lit.  The New Moon is when the Moon does not appear to be lit up at all, it is also starting its cycle over again, so it is “New.”  The Full Moon, as the name implies, is when the Moon is fully illuminated.  The Quarter Moons are when the Moon is halfway illuminated, 1st and 3rd Quarter simply denote how far the Moon is through its cycle.  To demonstrate the phases of the Moon, we used a foam ball (the Moon), recording the illumination from a light bulb (representing the Sun) as we moved it through different positions (according to Figure 1) around a stationary spot (representing the Earth).

                    

         1. New Moon                                         2. Waxing Crescent

      

               3. 1st Quarter                                  4. Waxing Gibbous

      

                 5. Full Moon                                    6. Waning Gibbous

    

               7. 3rd Quarter                                   8. Waning Crescent

As we can see, when the Moon is between the Earth and the Sun is when a New Moon occurs, this is because the illuminated side is facing away from us toward the Sun.  As the Moon moves around to the other side, more and more of it becomes illuminated until we have a Full Moon.  Since the Moon has to be between the Earth and the Sun to cause a solar eclipse, the Moon must be in the New phase to cause one.  Likewise, the Earth must be between the Sun and the Moon for a lunar eclipse, meaning lunar eclipses only happen during a Full Moon.  We do not have lunar and solar eclipses each Full and New Moon.  This is because the Moon’s orbit is tilted about 5 degrees from the ecliptic, so it only directly lined up with the Earth and Sun occasionally.

Part 2: Where is the Moon in the sky?

In this part, we showed that we can determine where the Moon will be in the sky at a given time if we know the Moon’s phase (and assuming we are at the equator).  This means the time can be determined by knowing the phase and position of the Moon.  To demonstrate this, I used a small circular calculator marked with East, on one end, West on the other, and Meridian in between.  To use this calculator, I placed it on Figure 1, so that at noon, East would be pointing toward position 3, West toward position 7, and the Meridian points directly to the Sun and position 1.  When the East is pointing towards the Moon, that is when it rises, and West is the time at which it sets.  The Meridian shows where the Sun is in the sky at the time the Moon is rising or setting, giving us the time of day.  For instance, the Moon during 1st Quarter rises at noon and sets at midnight, because the Sun is at the Meridian when East is facing position 3 and is on the opposite side of the Meridian when West is toward position 3.  Using this, we see that the New Moon rises at sunrise and sets at sunset, and, inversely, the Full Moon rises at sunset and sets at sunrise.

Part 3: The Moon’s Rotation

In part 3, we simulated the Moon’s rotation, using a foam ball and light bulb again.  First, we found a distinguishing mark on the ball, then moved the ball through all of the positions in Figure 1, keeping the distinguishing mark toward a stationary spot (Earth).  After that, we moved the foam ball through all the positions again, but this time keeping our mark towards the light bulb.  Through observing our own Moon, we can see that it is really more like the first procedure we did, with the same side of the Moon facing us at all times (even if it does wobble some).  This is because the Moon rotates counterclockwise around the Earth in the same time it takes to orbit around the Earth once.  Since the side of the Moon facing us goes through all of the phases, this means that the other side, the “hidden” side, also goes through all the phases.  So the “hidden” side of the Moon is not the same as the “dark” side of the Moon.

Part 4: Phases of the Planets

In part 4, we used our knowledge of the Moon’s phases to determine properties of other planets in our solar system.  First, we simulated what planets closer (called Inferior Planets) to the Sun than Earth would look like as seen from Earth.  To do this, we had a stationary point to represent our Earth and, between our stationary point and our light bulb, the foam ball to represent another planet.  We observed the illumination  of this planet as it moved through the positions as shown in Figure 2.  We then repeated this process, but with the foam ball farther away from the light bulb than our stationary point, as seen by the Superior Planet positions in Figure 2.  Figure 3 shows our observations of the inferior and superior planets.

Figure 3:

As we can see by our observation, inferior planets go through all eight phases as seen from Earth, while superior planets seem to only ever be in full or gibbous phases.  Given their positions closer to the Sun, we can usually only see inferior planets (Venus and Mercury) near sunrise and sunset.  On the other hand, superior planets (Mars, Jupiter, Saturn, Uranus, and Neptune) can be seen at different times throughout the night, varying throughout the year depending on our relative positions.  This helps to show that our solar system is based upon the Sun, not Earth centered.  If it were not Sun centered, we wouldn’t be able to see all the different phases of Mercury and Venus.

Overall, there a lot of things we can tell from the phases of the Moon and planets.  For instance, we can use the phases of the Moon to tell time.  With the planets we can use their phases to tell whether they are closer to or farther from the Sun than us.  These observations also helped us discover that Earth is not the center of everything, but just another planet in a very large universe.