A loss of confidence...

Alright. So I'm sorry. But you all have so many better things to do than to read this blog, so I don't feel too bad. I especially don't feel bad because there is a good chance that everything I am about to write is something you all most likely learned when you were in elementary school. I MUST have learned it at one point too, but clearly it didn't stick. This may make you lose any misplaced confidence you may have had in my knowledge of topics related to science, but that is a good thing, because then at least we all know what we are dealing with. In this case, we are dealing with someone (me) who has assumed this role of disseminating information that is only SLIGHTLY more trustworthy than the content of a textbook...if by "textbook" I mean a "Texasbook" .

Like I said: I should have known this, but I didn't.

You have probably seen the moon. If you have seen the moon, you may have noticed that its apparent shape in the night sky changes on a daily basis. If you are a REAL smarty pants you may have even heard words like "waxing" or "waning" or "crescent" or "gibbous." These are good words. Important words. A waxing moon is increasing in size, and a waning moon is decreasing in size. A crescent moon has a concave curve, while a gibbous moon has a convex curve. These are things that people know, for the most part. And many people also understand WHY these shapes occur... but I did not. I'm not too proud to admit it. I always assumed that the phase of the moon, that is the "fullness" of the moon, was simply determined by the shadow of the earth on the moon...but this explanation wasn't satisfying to me because I couldn't figure out how the earth, a spherical object, could cast a shadow on the moon that was anything other than round. How could the shadow of the earth create a gibbous moon, a moon that is more than half full, with a CONCAVE shadow?

It didn't add up. But luckily there are resources on the internet that can explain this phenomenon in a single figure, such as the one presented below from the website www.moonconnection.com.


So really the earth's shadow has nothing to do with it (except in the case of a lunar eclipse)! Half of the moon is always illuminated by the sun...what changes is our perspective on the moon as it orbits the earth!!! The inner circle of moons shows how the moon is ACTUALLY illuminated over the course of a cycle, and the dotted radii in the diagram show our changing perspective over the course of a lunar cycle. This changing perspective is responsible for the shapes we can see in the diagram's outer circle of moons. And finally, finally, finally I understand how it is possible to have a gibbous moon. But I still have much to learn about how to walk on the moon: