As my first post since my hiatus to finish my degree, I thought I’d bring up a timely topic. Over on the Moon Zoo forums, one of our most active volunteers and forum moderators, a woman who goes by the name of Jules, posted about her time at the Times Cheltenham Science Festival.
You can click the image to enlarge it. I strongly suggest reading it before moving on.
Let’s Look at the Text
The particular offensive paragraph is the fourth:
“As you have noticed the Moon goes through a number of phases, from full Moon, though to new Moon and back to full Moon. This is because as the Moon orbits, the sunlight that makes it visible can be blocked by the Earth. This means that the amount of the Moon that is illuminated depends upon where the Moon is along its orbit.”
Interesting. I would ask why you can see the sun and moon in the sky at the same time if Earth’s shadow is blocking light, causing the Moon’s phases.
You can also think about a lunar eclipse, such as the one that was visible just this week from most of Europe, Africa, and Asia.
What’s Wrong with This
If you haven’t caught on yet, this is not why we have phases of the moon. The moon orbits Earth approximately once a month. As it orbits, one half is lit by the sun, and the other half is in its own shadow, just as Earth is always half-lit by the sun and half in its own shadow for night. Since the moon keeps one face always looking at Earth, it is slowly rotating relative to the sun and so each point on its surface goes through about two weeks of daylight and two weeks of night.
For a really cool movie illustrating this made by an amazing graphic artist, educator, and scientist, check out this link (22 MB, MOV format).
In other words, this sign is wrong. Blatantly wrong. Clearly wrong. Any little amount of thought put in would indicate that this is wrong (why do we see the moon in any phase other than full at the same time as the sun? we shouldn’t if Earth’s shadow is what causes the phases …).
And yet this sign looks nice, is shiny, has several corporate sponsors, and is presented at a large science festival.
Two More Things
The poster also lists a distance to the Moon as 384,000 km. This is correct. Until Jules pointed out to me that the sign claims this is the distance between the Moon and Sun (which is 149,600,000 km ± 384,000). The 384,000 km is the distance between Earth and the Moon.
A final incorrect statement has to do with the third paragraph which states that the moon having the same side facing Earth has been “very useful as astronomers have been able to map the surface of the Moon using telescopes.” This doesn’t really make sense. I suppose one may be able to claim that it would take us twice as long to map the Moon if we saw the whole thing, but then the nice part would be we’d be able to map the whole thing. We had to wait for the first Soviet flyby to return photographs of the lunar far side before we could even begin to guess what it was like.
This gets to the heart of two of the main reasons I do this blog. (1) It shows that all because you have a big fancy sign does not mean that you are right. People have to be ever-vigilant and questioning or they risk falling for something like this. (2) I think people learn better by examining misconceptions / mistakes that they make or others have made. The sign is clearly wrong, but you may not have known why it was wrong — it may have just sounded weird. So now with the actual explanation for phases, you can contrast that with the sign’s explanation which can make it easier to remember.
On a related theme, this sign actually reminds me of a sign I saw in a science museum a few years ago. It was talking about the force of a car crash and how much destructive power a 60 mph (100 kph) car crash has. And then the museum decided to throw in another line about how, “But, according to the Heisenberg Uncertainty Principle, if conditions had been a little different the accident may not have happened at all!”
Yes, that was a science museum. Using a fallacious appeal to quantum mechanics.
Keep a lookout, folks, these things are everywhere. To distort a phrase, the price of knowledge is eternal vigilance against pseudoscience.