The only object that emits a substantial amount of visible light in the Solar System is the Sun. Everything else we only see because it is lit up by the Sun. Thus every object has a day side and a night side. A side that it lit up by the Sun, and a side that is not. When we view objects in the Solar System how much is lit up will depend on the relative position of the viewer, the object and the Sun. If the object moves over time then it will go through phases as a different fraction of its surface is visible to the viewer.
The phases of Earth’s Moon are the most common example of this, though nothing about it is unique to either Earth or her Moon. The same phenomena occurs on all planets that have moons.
Laboratory Tools
In this lab we will be using the Lunar Phase Simulator developed by the University of Nebraska – Lincoln. This simulator shows the phases of Earth’s Moon as it orbits the Earth. The main box shows the Earth and Moon from a top down view. Arrows indicate the direction of sunlight. The box below Animation and Time Controls, allows you to start the animation and control its rate. You can also advance time in units of days, hours or minutes, though not much happens in minute. Next to this box is Diagram Option. Check the box for show angle and show time tick marks. The upper right box Moon Phase, shows how the moon is illuminated given its location and the name of that phase. The pull down menu can also advance the moon to that phase. The box below, Horizon Diagram, shows the view of the celestial sphere.
Assignment
In this lab, for each of the phases of the moon listed below determine from the simulator the angle the moon makes with the sun, the percent of the moon illuminated and the time of day it will be for an observer when the moon is directly overhead. Please make sure to create a table in the program you use to create your report.
| Phase | Angle with Sun | Percent of Moon Illuminated | Time that Moon is Overhead |
| New Moon | |||
| Waning Crescent | |||
| First Quarter | |||
| Waning Gibbous | |||
| Full Moon | |||
| Waxing Gibbous | |||
| Third Quarter | |||
| Waxing Crescent |
Questions
- The phases of the moon are described as waxing or waning and crescent or gibbous. What do these terms mean?
- What phase must the moon be in for a solar eclipse to occur? How about a lunar eclipse?
- For an observer on the moon if the moon is in the new phase what phase would they see the Earth being in?
