Hey, let’s take the Moon out for a spin… but we’re too late! It already does spin!
And I can prove it. Just watch Q & BA Episode 5: Spin Doctor and you’ll see how.
Viewing options:
Watch it right here, right now!
Download it directly from LibSyn.
Download the audio only version from LibSyn.
Once again, I’m trying something new. I’ve been asked to have two separate feeds; one for audio and one for video. Let’s see if this works!
Subscribe to AUDIO ONLY VERSION via iTunes.
Subscribe to VIDEO VERSION via iTunes.
Show notes
The Question:
The question was sent in by Mark Tillotson, of Emmaus, PA:
What would we experience if the moon was not ‘locked’ in it’s rotational period with the earth?
Would we see anything different on Earth? Would the tides be different? Would the lunar recession be different (moving away from Earth faster or slower)?
Images and Links
The essay I wrote about tides, the Moon’s rotation/revolution lock, and its recession can be found on my Misconceptions page.
The lunar phases image is from the amazing Lunar and Planetary Observation and CCD imaging website of Antònio Cidadão; specifically, his animations page.
The far side of the Moon image is courtesy NASA and the Galileo probe.
I bookmarked the site with the revolver image so I could link it here, but I appear to have lost it (it was a public site, like from a museum or government). Oh well. Don’t shoot me.
March 4th, 2007 at 9:59 pm
A great explanation of a basic, easily observed astronomical event, Phil. In college I took a basic science course; one of the problems was to explain the phases of the moon using simple models.
March 4th, 2007 at 10:37 pm
Is there an mp3 version of the audio-only version? I’m only seeing a link for an mp4 version, which my mp3 doesn’t support. Not all of us have I-pods, you know
March 4th, 2007 at 10:56 pm
Loved your hate mail addy!
March 4th, 2007 at 11:44 pm
Yeah, second the LOL at the hate mail address. Topical much.
March 4th, 2007 at 11:55 pm
I must add that the special effects were splendid. You really splashed out this time around!!
March 5th, 2007 at 12:34 am
Hey, Phil: as Shnakepup points out you have posted your video version twice on iTunes. I tried playing the audio-only version and got video.
March 5th, 2007 at 1:07 am
Phil, is that the only working email address of yours? Your contact page still has badastro at badastronomy dot com.
(And remember, “I saw the crescent / You saw the whole of the moon”…)
March 5th, 2007 at 4:50 am
Em-mouse?! OK, I know we talk funny here, and I guess we spell things wrong too. But for the record it’s pronounced “ee-may-us” (accent on “may”). And if you get email from Kutztown, “Kutz-” is pronounced like “puts”, not “cuts”.
PA Dutch country, “Throw the cow over the fence some hay, now!”, it’s a lifestyle.
:^)
March 5th, 2007 at 5:07 am
At 4:32-4:35, you say “… and so over the course of just a day or so, you would see the entire surface of the Earth.” You mean “Moon”.
Also, yes the audio feed downloads a video file.
March 5th, 2007 at 7:32 am
This is very useful. Thanks. I have, in the past, had a hell of a time explaining to some people that the moon does, in fact, rotate. It usually involved me holding up an orange, or some other handy spherical object, and slowly rotating in place as I show the consequences of a non-tidal locked situation. And these are college educated people in technical fields. It’s a pervasive myth and the tidal locking is the core cause.
How about one about how there actually is gravity in orbit, and that the “zero gravity” is just, as Buzz Lightyear might say, falling with style?
March 5th, 2007 at 8:30 am
I enjoyed the Q&BA, but I don’t think that you fully answered the guy’s questions. You got the “what would we see” part, but not the question on tides or recession.
Neat special effects.
March 5th, 2007 at 9:48 am
I just noticed on my own that the audio file wasn’t set up correctly. I fixed it. D’oh!
I know I misspoke when I said Earth and not Moon, but I decided to not record the whole thing over again. I was hoping it was obvious it was a simple slip of the tongue.
Also, I would love to talk about tides and recession, but like I said int he vid, that will take too long. These videocasts really can’t be much longer than 5 or 6 minutes for now because of filesize; even the medium resolution Quicktime version is 30+ Mb! In Flash it’s not such a big deal, but I have hundreds of people downloading through iTunes so I’m trying to keep the length down. If I can figure out a simple way to do it, I’ll cover that part of the question as well.
March 5th, 2007 at 10:34 am
Great show. BTW Galactus not Galacticus.
March 5th, 2007 at 11:29 am
Is there no way that the moon actually rotates (as seen from the Earth) at large time scales?
March 5th, 2007 at 11:47 am
rvr, no the moon is tidally “locked”, which means that any drift in the rotation of the Moon is actively compensated by the tidal forces between the Earth and the Moon.
March 5th, 2007 at 12:34 pm
Excellent show!
March 5th, 2007 at 12:37 pm
Once again, you used really effective, simple props. The ball with the two sides was a great way to show the fact that the moon is always facing the Earth. Humor and astronomy combined together. It’s truely a great thing.
The book on the table was very fitting. These videos are always the highlights of my mondays!
March 5th, 2007 at 12:43 pm
My favorite one so far.
March 5th, 2007 at 4:25 pm
clambake,
Thanks for the correction. I got a laugh at the pronounciation of Emmaus but I had forgotten that it is not obvious to everyone outside of PA so I didn’t include a pronounciation guide. It’s a biblical name so some people may have heard it at church. I’ve heard many variations and quite a few people don’t even try to say it.
But here in PA, Emmaus and Kutztown are not even close to the wierdest town names!
Mark “the Submitter”
March 5th, 2007 at 8:11 pm
PK: Well, the lock is not complete, there is still some movement (the libration). I wonder whether the moon could rotate (as seen from Earth) in very tiny bits, which would result in a measurable shift at large time scales.
March 5th, 2007 at 8:52 pm
Is libration due to the moon wobbling back and forth like a pendulum, or due to the fact that the moon’s orbit is eliptical, not circular, so the angular velocity of its orbit is not constant? Or some of both? (I always assumed it was the later, but I don’t know this for a fact.)
March 5th, 2007 at 8:57 pm
P.S. Ths sound was very faint, and my office A/C/heat fan turned on just as I started to listen, making it even harder to hear. The first 10 seconds or so of the intro sounded fine, but then it got muffled, so it might have been the recording. Does anyone else have the same problem? I’m listening on a Mac Powebook with the volume cranked all the way up, OS X 10.4.8, Safari, just clicking on the image to start it. (I also tried the Google version, which openned up a new Safari window, ran with a bigger image, but sounded pretty much the same.) The A/C has gone off now, so I’m going to try again…
March 5th, 2007 at 9:06 pm
A lot better without the fan noise, but still quite faint. The volume dropped right when you cut to the graphic with Mark’s question. (You’ll be happy to know that mispronouncing Emmaus came through loud and clear
March 5th, 2007 at 9:19 pm
Jeez Phil you’d think an astronomer would know the moon doesn’t revolve around the poles like you kept showing, guess we know why you’re the “Bad Astronomer” now don’t we.
Nice little pod cast keep them up.
March 5th, 2007 at 9:45 pm
Phil has a really neat and tidy room. I assume that is his room. Maybe it’s a computer room that doubles as a guest bed room or something. But in any case… he keeps it neat and tidy and I respect him for that.
March 6th, 2007 at 1:30 am
According to Wikipedia, the libration is primarily caused by the eccentricity of the orbit. Also on Wikipedia is an animation for libration. You can really see the backwards-and-forwards motion.
I think you could have some drift if the tidal locking hasn’t been completed yet. If the moon starts with a different rotation, it will be slowed down (or sped up) over a long period. However, I do not see a mechanism to get out of tidal locking (in a stable equilibrium system).
March 9th, 2007 at 1:12 pm
Phil…don’t be one bit put off by slips of tongue, cheap sets, neat rooms, or over-critical comments — astronomy topics can soemtimes get very complex after all, however, you continue to make it look easy, which is, I guess, your main objective. Continued success.
March 11th, 2007 at 9:20 pm
Er… sorry if the neat room comment somehow overshadowed the overall worth of the youtube-cast. I liked it, and the explaination was understandable and informative. Seriously…in addition to the nice bedroom… Sorry if that seemed to off-topic