
A Year of the Moon in 2.5 Minutes - it wobbles more than you might think [video] - ColinWright
http://youtu.be/F9pVaTQinIw
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rootbear
This animation was produced at the Scientific Visualization Studio at NASA
Goddard Space Flight Center. I work in the Studio and the visualizer who
created it is in the next office over. All of our work is on the web at
<http://svs.gsfc.nasa.gov>. This animation can be found at
[http://svs.gsfc.nasa.gov/vis/a000000/a003800/a003810/index.h...](http://svs.gsfc.nasa.gov/vis/a000000/a003800/a003810/index.html)

I agree it would be interesting to see an animation that eliminated the
rotation and scaling and depicted only the wobbling. Producing that might be
harder than you think, the coordinate systems and transformations involved in
making an animation like this get complicated pretty quickly.

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alanfalcon
Fun trick:

Find a high res picture of the moon. Say this one: [http://universe-
beauty.com/albums/userpics/2011y/04/19/1/18/...](http://universe-
beauty.com/albums/userpics/2011y/04/19/1/18/The-Moon---05.jpg) Go to
<http://www.tineye.com/> (Reverse Image Search) and search for that image.
Click one of the results (make sure it isn't just the same exact image) and
then click the "switch" button repeatedly to wobble the moon. Because Tin Eye
matches the rotation and scale of the images, it creates a neat effect.

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raghus
It is quite amazing that in spite of the moon's rotation about its own axis
and our (the Earth's) revolution around the sun where the moon comes along for
the ride, we still only ever see just a bit over 50% of the surface of the
moon. That takes some amount of dexterity on the part of the moon.

~~~
bdhe
This is very common among natural satellites. Here's the phenomenon:
<http://en.wikipedia.org/wiki/Tidal_locking> (Look at the list of tidally
locked bodies)

~~~
raghus
I did not know that, thank you.

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nfg
Libration: <http://en.wikipedia.org/wiki/Libration>

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cousin_it
The sensation of movement seems to be mostly caused by rotation and scale
changes, not wobbling. I'd like to see a video that compensated for all
effects except wobbling.

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ColinWright
Clear explanation of the different forms of libration:

[http://www.nmm.ac.uk/gcse-astronomy/sun-and-moon/moon-
moveme...](http://www.nmm.ac.uk/gcse-astronomy/sun-and-moon/moon-movement/the-
moons-movement/*/viewPage)

~~~
ryanklee
Link was 404

[http://www.nmm.ac.uk/gcse-astronomy/sun-and-moon/moon-
moveme...](http://www.nmm.ac.uk/gcse-astronomy/sun-and-moon/moon-movement/)

~~~
ColinWright
How bizarre - I copy/pasted it from the URL bar of my browser.

Thanks for the corrected link.

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rman666
Slightly OFF TOPIC - I've been trying to find references to any
articles/stories about how early astronomers first estimated the distance from
the Earth to the Sun (using only observational astronomy). It appears the
distance was first estimated in multiples of the distance from the Earth to
the Moon. If you happen to know of any quality articles about how these
estimates were made (and how a modern amateur astronomer might duplicate
them), I'd appreciate a link. Thus far, Google searches have only been mildly
useful.

~~~
sehugg
It hinges on observations made during the transit of Venus across the Sun:
<http://en.wikipedia.org/wiki/Transit_of_Venus>

Eli Maor wrote a great book "Venus in Transit" that accounts this multi-
century quest to accurately measure this event, which occurs very rarely and
requires accurate timekeeping across large distances to compute the
triangulation. It's a fascinating story.

~~~
sehugg
BTW, the next transit is in June 2012, and it's likely the last opportunity
any of us living today will get to see it:
<http://www.transitofvenus.org/june2012/where-to-be>

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smallblacksun
The title claims that it is a year of the moon, but the description says that
the images are from 2011 - which isn't over yet. So is this a year of the
moon, or six months?

~~~
panacea
It's an animation.

~~~
ColinWright
Only in the sense that it's moving. These are, apparently, actual images of
the Moon. I suspect it's a typo, and the images are from 2010, but I don't
know.

~~~
panacea
"The animation archived on this page shows the geocentric phase, libration,
position angle of the axis, and apparent diameter of the Moon throughout the
year 2011, at hourly intervals. The Current Moon image is the frame from this
animation for the current hour.

This marks the first time that accurate shadows at this level of detail are
possible in such a computer simulation."

It's a sim.

~~~
ColinWright
Hah - interesting. I stand corrected, and I thank you.

~~~
panacea
NP. It was non-obvious from the YouTube description.

I had to dig around for confirmation it was a sim. I was scratching my head
after your mild assertion.

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crististm
When I saw moon libration for the first time I though this should have made
people understand that Earth is spherical. But nobody noticed it for a long
time...

~~~
InclinedPlane
The Earth has been known by learned men to be spherical for well over 2,000
years, and it's circumference was first measured through experiment by
Eratosthenes over 22 centuries ago.

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JackWebbHeller
Coincidentally, there is a lunar eclipse tonight. If you're in the UK, take a
look at 9:15PM this evening - I'm afraid I don't know how visible it will be
elsewhere.

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ulvund
Wobbles with respect to what?

~~~
nadam
With respect to an inertial frame of reference I guess. (A frame rotating
relative to an inertial frame is not an inertial frame anymore.)

Edit: No, I was wrong. It wobbles with respect to someone viewing it from the
the earth looking towards the moon. (Which is not an inertial frame of
reference.)

