Education & Inspiration
Education Matters:
Standing in the Shadow of the Moon
We are familiar with many types of shadows, but two of the most rare and exciting ones relate to the Moon’s and Earth’s shadows.
By Brian Kruse
Brian Kruse
On May 26, 2021, the author watched as the Moon passed into Earth’s shadow. He captured this image from Los Altos, California.
[Brian Kruse]
Editor's note: Educational eclipse content is free and available for all
Remember back to your first eclipse, that moment when you stood in the Moon’s shadow. What was the experience like? How did you respond to the awesome spectacle in the sky? Did someone help you understand what was happening, or did they just tell you? How have you mentored others to come to a deep understanding of eclipses, taking care to not reinforce any lingering preconceptions? Or reduce their visceral experience to a set of facts and figures? Drawings and words only go so far in promoting deeper understanding so people have a true internal model of what is taking place, of the lunar shadow. The use of modeling tools and direct experience with their manipulation can help people’s cognitive understanding, complementing the awe and wonder they feel when experiencing the actual phenomenon. It all starts with the basics, a source of light, and an object to block the light.
We are all sources of illumination to foster deeper understanding, the trick is to not eclipse the experience with our own preconceptions.
An explanation of a shadow is something we generally think of as intuitive. It turns out shadows, particularly when it comes to those large-scale ones celestial objects produce, are not as intuitive as we might think. Shadows make their appearance in classrooms very early on, and the subject forms the basis for two Astronomical Society of the Pacific research projects with preschoolers and first graders. In both projects, learners used a flashlight and a figure of a bear to create shadows, changing their characteristics such as length and direction depending on the position of the light. First grade students also went outside to track the changing pattern of shadows with the actual Sun. Basically, they learned the creation of a shadow requires a light source, and an object to block the light. So far this is fairly basic and intuitive.
Scaling the aforementioned activities up to larger objects starts to create challenges for learners, even those who left their school days far behind. Walking through a city it is relatively easy to recognize there is a “shady side of the street” with buildings blocking the sunlight from reaching the sidewalk. This provides a pleasant, cooler place to walk on a hot day. Or we put up an umbrella to create shade (in this case another word for shadow) in our backyards. People may even have an understanding of the shadows mountains create, and how climbing to the top allows them to see one side in sunlight and the other in shadow. In all these cases, the shadows still have a lot of ambient light illuminating the scene. Cases where an object blocks enough light to create darkness might include closing a door to someone’s room at night, the darkness under the bed, or a house with blackout curtains even when the Sun is shining brightly.
"The experience of standing in the shadow of the Moon is rarer, partially due to the smaller size of the shadow. ... standing in the total shadow of the Moon is limited to a narrow band."
NASA
On August 21, 2017, the author captured this photograph of the Moon blocking the Sun. From his vantage point in Ochoco National Forest, Oregon, he stood in the lunar shadow.
[Brian Kruse]
Scaling our objects still larger to the size of planets starts to create misconceptions about shadows. On a dark evening, think about how someone might respond if you ask them to explain why it is night. Would they say it is dark out because we are in the shadow of Earth? A few might say it is dark because we are in the shadow of the Moon. The latter case was actually mentioned in an article on npr.org. (The workers in the NPR story were pouring concrete in the shadow of Earth, not the Moon as was reported.)
And what about the changing lunar phases? How do people explain those? A relatively common answer is the darkened parts of the Moon are due to the shadow of Earth. Going back to shadow basics and the need for a light source and something to block the light, we can demonstrate with simple materials the light source is the Sun, and the object blocking the light in the case of nighttime is Earth, or the Moon itself in the case of its phases.
Eclipses = shadows
The question might arise: Do we ever experience the shadow of the Moon, or does the shadow of Earth ever encompass the Moon? The answer in both cases is a resounding YES!
While we can stand in the shadow of Earth 365 days per year, the Moon only passes through or touches it between two and four times per year during a Full Moon. At those times, if we are on the nighttime side of Earth, we share the experience of Earth’s shadow with the Moon. Thus, many people can experience seeing the shade of Earth encompass the Moon. (This is known as a lunar eclipse.)
The experience of standing in the shadow of the Moon is much rarer, partially due to the smaller size of the shadow. While the Moon will either completely or partially block light from the Sun at least twice, and up to five times, per year, fewer people are able to have a direct experience of the Moon’s shadow.
BRIAN KRUSE manages the formal education programs at the Astronomical Society of the Pacific.
The total solar eclipse of August 21, 2017, was probably the most accessible eclipse for the people in North America. While standing in the total shadow of the Moon is limited to a narrow band, even many people unable to travel to the path of totality were able to see a partial eclipse. Unlike lunar phases, which are due to the Moon’s changing position as it orbits Earth, a partial eclipse is where the Moon only partially obscures the Sun. A great many people experienced an eclipse for the first time, and there was a concerted effort to help them understand what it was they observed.
The two upcoming solar eclipses (an annular in October 2023 and a total in April 2024) are opportunities to recapture the excitement from 2017, and bring the awe and wonder to whole new audiences. Even a partial eclipse has us standing in the shadow of the Moon. ✰
(Originally published March 31, 2023)
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