Explaining Fishing-Related Phenomena

12.A Develop and use a model of light in the Earth-Sun-Moon system to describe why the Moon changes color during a lunar eclipse.

12.A Develop and use a model of light in the Earth-Sun-Moon system to describe why the Moon changes color during a lunar eclipse.

• Light from the Sun travels through space in straight lines until it reaches the Earth, the Moon, or both.
• Some of the sunlight striking Earth's surface is reflected back toward space.
• Sunlight hits the half of the Moon that is facing the Sun. This lights up, or illuminates, half of the Moon at all times.

The light bouncing or reflecting off of the Moon can scatter in many directions. Some of the reflected sunlight travels to the Earth, where the eyes of an observer (or a telescope or camera!) can gather this moonlight. This is how we see the Moon in our sky (except when there is a new Moon!).

When the orientation of the Earth-Sun-Moon system causes a full Moon, the Earth can block direct sunlight from reaching and reflecting off of the Moon, so we would expect the Moon to go dark. However, it stays lit and turns a reddish color, which means light is somehow getting to its surface:

• White light passing through the Earth's atmosphere bends (refracts) or changes direction by the gasses (including water vapor) and other particles in the atmosphere so that some of the light reaches the Moon.
• Less light than normal (but still more light than none) reaches the Moon's surface after passing through the atmosphere and reflects back to Earth so we can see the Moon.
• As this happens, the bluer light that makes up the white sunlight gets scattered disproportionately (more than red) in the atmosphere.
• More of the redder light that made up the white sunlight passes through the atmosphere. This is the light that reaches the Moon’s surface and reflects off of it to Earth so the Moon looks reddish.
• The red light is what gets through the atmosphere best, and then that red light is also bent by the atmosphere so it shines on the Moon.

If students are having trouble explaining the changes during a lunar eclipse, remind them that they can refer back to the investigation notes they have in their notebooks. They can consider which parts of the systems they investigated are similar or different from the lunar eclipse and what they represent. If students are struggling to represent ideas such as the changes in light as it moves through the system, encourage them to use the resources gathered in their Progress Trackers.