Phases of the Moon and Planets

Phases of the Moon and Planets

Part One: Phases of the Moon

The lab begins with an exploration of the moon's phases as it moves relative to the sun and the Earth. The following pictures represent the moon's phases in order, beginning with the new moon and ending with the waning crescent that precedes the following month's new moon. As the foam ball (the moon) changed positions around the camera (the Earth) relative to the lamp (the sun), we observed the shadow projected on the moon and how it appeared from the Earth.

Because a solar eclipse occurs when the moon blocks sunlight over a portion of the earth, the moon must be in the new moon phase. During this phase, the moon is between the sun and Earth showing no signs of a lit face.

A lunar eclipse occurs when the Earth is between the sun and moon. When this happens, we have a full moon and the visible portion of the moon appears to be entirely lit.

Part Two: Where is the Moon in the Sky?

The moon's phases happen to be visible at different periods of the day. If we were to stand on the equator, the moon is in the sky from noon to midnight during the first quarter. A full moon is visible from sunset to sunrise. The third quarter can be seen from midnight to noon. A new moon is in the sky from sunrise to sunset. The sun is at the meridian at the midpoint of these time frames.

Part Three: The Moon's Rotation

By moving the foam ball around a midpoint representing the Earth, we discover that the the dark side of the moon and the hidden side are not the same, Because of the timing of the Earth's rotation and the orbit of the moon around the Earth, we always see the same face of the moon from the Earth's surface. This surface, however, sees different shadows throughout the 29 day cycle of the moon's phases. Though we always see the same face, these shadows occur because of the moon's change in position relative to the sun throughout the month.

Part Four: Phases of the Moon and Planets

Using a light bulb to represent the sun like in Part One, we put the superior and inferior planets' phases to the test. A foam ball orbiting the light between the camera and the sun represents the inferior planets like so:

These phases, in order, represent an inferior planet's orbit as seen from the Earth's surface. From our point of view, the inferior planets have clear phases, just as our moon does. This is clear from the shadows on the foam ball above. The shadows happen to occur in reverse order of those projected during the moon's phases, however. 

The superior planets have a different set of phases that can be observed from Earth, as are seen in the experiment pictures below:

Unlike the inferior planets, the superior planets appear to skip phases. The planets beyond Earth appear to be lit by the sun's light almost always with the occasional waxing or waning crescent phase. The shadows that sometimes appear on the superior planets are only vaguely apparent in the photos above. They're less prominent that the shadows we see on the inferior planets.

The superior planets will likely appear to be brightest, possibly like stars, when they are closest to Earth in their orbit. When this occurs, these planets are visible at night, making them easier to see.

Part Five: End of Lab Questions

Our models show that a lunar or solar eclipse do not occur with each new moon or full moon phase. This is because the moon orbits the Earth on a plane that is not necessarily the same as the plane the Earth orbits the sun. Occasionally the moon does fall on the same plane as the sun and Earth, though, and an eclipse occurs.

The reason there is a difference between the 27.3 days the moon takes to orbit the Earth (the sidereal month) and the 29 days it takes the moon to see all of its phases (the lunar month) is due to the movement of the Earth around the sun. Because the Earth is constantly moving in its orbit around the sun, the moon takes a slightly longer amount of time to reach its original position relative to the sun and Earth than it would if the Earth was still. A really great animation of this phenomenon is here: 

http://www.sumanasinc.com/webcontent/animations/content/sidereal.html

If you were to follow the Earth and moon in their orbit around the sun, you would not always see the same side of the moon. This is because from behind the orbital system, you will see the hidden part of the moon when it is between you and the Earth and you will see the normal side of the moon when the Earth is between you and the moon.

In the Earth centered model of the solar system, Venus is always between the Earth and Sun. If this was true, we would never see Venus in the fully lit phase.

Superior planets can be seen at Midnight because they orbit outside of the Earth's orbit relative to the sun.

The inferior planets are Mercury and Venus. Mars, Jupiter, Saturn, Uranus, and Neptune are superior planets. 

In this lab, I learned that the planets go through phases just like the moon does. I also learned that these phases are influenced almost entirely by the planet's position in respect of the Earth and Sun in the solar system. The difference between a sidereal month and lunar month are also surprising, as I did not think to consider that the Earth's movement around the sun would affect how we view the moon's movement.

The point of this lab was not only to understand lunar and planetary phases, but to help understand the thought process required in discovering the sun-centered universe model. The lunar phases of the planets around the sun prove that the planets must orbit something other than the Earth. This lab helps us understand the movement of the moon and planets in the sky, which is a basic point of astronomy.