A Lesson in Perspective from the Moon

“It all depends on how you look at things.” You hear that common phrase applied to many kinds of issues. If you doubt that, here is a lesson in perspective from the Moon. First, let’s look at the facts about the Moon and what we think we see when we look at it. Astronomer Bob Berman’s article In the October issue of Astronomy magazine contains some interesting facts comparing what we see and reality. 

How big is a full moon? Berman points out that it would take 180 full moons stacked on top of each other to fill the space between the horizon and a point directly overhead. The Moon is very small from our perspective, even though it appears large, especially when it’s near the horizon. How much brighter is the Sun than a full moon? The answer is that the Sun is 450,000 times more luminous. The Moon is a very dim object, just a little brighter than coal and much dimmer than dark green leaves. If you remember albedo from your high school physics class (the proportion of the incident light reflected by a surface), the Moon’s albedo averages 11, and a dark green forest is 15. Charcoal is 5.

Why does the Moon look so bright on a clear night when the Moon is at full phase? The answer is a lesson in perspective. Our eyes are designed to give measures of brightness based on what surrounds the object we’re observing. From our perspective, when we look at the Moon, we see an object in front of a black background. Our brain tells us that the Moon is white because its surroundings are completely black. 

Astronauts have been to the Moon and found that most of its surface is basalt, a black volcanic rock. Basalt reflects very little of the light coming to it from the Sun. So compared to Venus or Jupiter, which have clouds efficiently reflecting light from the Sun, the Moon is a dim and dark object. 

On a human level, there is a lesson in perspective. An old joke tells about the response a man gave when asked if his wife was beautiful. He responded, “Compared to what?” The same issue arises when someone asks if Christianity offers any advantage to a person or the world in general. Compared to all human philosophies, the answer has to be that the world and humanity have benefitted from the life and teachings of Jesus Christ. We are talking about the actual teachings of Christ, not the perversions such as the Crusades, the inquisitions, or ethnic struggles. What have atheism and secular humanism done to benefit the people of the world?

Jesus gave a lesson in perspective in Matthew 5:14-16 when he said, “You are the light of the world … let your light so shine before mankind that they may see your good works and glorify your Father which is in heaven.” The Sun is the source of the small amount of light we get from the Moon. Jesus is the source of the light we give to the world. The question for those of us who are Christians should be, “What is our albedo?” How much of what Jesus shines on us do we reflect on a very dark planet?

— John N. Clayton © 2021