Sunday, December 1, 2019

The Collision that Formed the Moon

I was poking around YouTube looking at videos about where the Earth's Moon came from. The currently accepted theory is called the Giant Impact Hypothesis. Though details differ, the main idea is that a smaller planet collided with the early Earth, and the Moon arose from the resulting debris. This hypothesis continues to be tweaked to this day, and other hypotheses continue to be proposed, all because details remain in the existing evidence that are unaccounted for. It's both delightful and a little surprising that the research is still quite active.

I was looking for an up-to-date simulation of the Giant Impact as opposed to an artist's interpretation. I was hoping that, given the current state of computer simulations, there might be something amazing available. There are older videos on YouTube about the Giant Impact which use pretty impressive artist's interpretations. But artists will sometimes take liberties with the physics if it makes the animation more engaging. What I wanted my students to see was a computer simulation that is based on a mathematical model that is allowed to run unedited and unimpeded. Like this:



This is clearly a simulation, probably run on a supercomputer. There is no question that the imagery is based on a model. You can even see the individual elements, almost like little blobs, for which calculations are being run to determine the next state of each blob.

Eventually I came across this video:



I loved this simulation. You can see the resemblance to the one above. The video is obviously a clip from a longer video, but no credit was given. So I hunted and hunted until I found the source:



This is a longer video featuring the work of Dr Robin M Canup, who is also narrating. Dr Canup is associated with the Southwest Research Institute in Boulder CO, where she has used supercomputer simulations to create and build her Moon-formation models. She has also participated in the production of "data-driven cinematic animations," like the one in the video above.

This video is a preview of a portion of a Fulldome Planetarium show called "The Birth of Planet Earth," produced by Spitz Creative Media, the Advanced Visualization Lab of the National Center for Supercomputing Applications, and Thomas Lucas Productions, Inc., set for release in 2019. (More details in this report and in this website).

As nice as this 2018 mini-documentary is, I still wanted just the simulation, so I edited it out of the video as its own clip and stripped the audio. I thought about adding some kind of background music, or using music from the original video. Dr Canup's narration was pretty good, but just not lined up with the simulation clip. I really liked the idea of the female narrator also being the physicist whose work this was - something I'd be proud to point out to my students. So I copied the audio of her narration (with the music), added it to my clip, tweaked the timing a bit, faded the ends, and then had to stall the beginning of the clip to fit the whole audio. I built an elaborate fade-in with the visuals so the stall would feel more natural. It also allows the viewer a chance to focus on Dr Canup before the visual effects of the collision take over. Here is the final result:



A final note: Dr Canup appears in an earlier, similar production created for the History channel in 2007. There's a low resolution version of it on YouTube.

Cross-posted to Teaching Is . . .
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New Demonstrations

A couple of new quick labs for my students this fall. Thanks physics Twitter!





Cross-posted to Teaching Is . . .
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