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3D models to help visualize movement of sun and stars across our sky

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#1 Starry_Spruce


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Posted 09 December 2023 - 10:31 AM

Hi all,


I am looking for ideas about building or curating a model, or models, that will help the general public/young folks visualize the position and movement of the earth in the solar system and in relation to the celestial sphere. Both daily movement (earths rotation) and seasonal movement (earth's orbit around the sun). The hope is to illicit a connection between the solar system model and the actual observed movement of objects (especially the sun) across the sky. This would be temporarily set up in a public space—for a season or so. 


I'm basically picturing some sort of armillary sphere, but something that is a little bigger and hopefully more intuitive than the small brass globes you see online. Too dense. I'm also thinking that an external heliocentric model that can clearly show the solstice and equinox moments would help tie things together, though how to effectively and simply draw the connection between the models, I'm not sure. Some people still think the earth's axis of rotation tilts with the seasons.


Any ideas about how to create something that would be intuitive to the general public walking up to such a structure(s)? Accompanying explanatory text (such as on an interpretive panel) would likely still be needed.



Edited by Starry_Spruce, 09 December 2023 - 10:32 AM.

#2 PolyWogg


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Posted 09 December 2023 - 10:46 AM

It's a great idea SS, and I've seen lots of people do different things without 3D modelling that could easily be adapted. I don't. For me, I think the three things you might want to try are:


1. 3D "globe" of the moon, complete with craters, marbling, etc...People always see it looking like a flat ball with markings on it, but rarely with a textured surface. Even a segment, aka "pick a crater", that shows a crater that is about the size of your town, or your county, etc. Something that allows them to see it "to scale" for something local.


2. You can do Sun + Earth + moon, but I'll warn you in advance that scale goes out the window pretty fast. If you do it to scale, then the objects are too small to be fun and interactive. Or too large to be manageable. It can do your solstice, eclipses, etc. An easy "3D" option would have a flat surface that rotates in concentric circles with the "ball" (aka earth and moon) revolving around (like looking DOWN on the system) so you only see the half-circle.


3. Solar system is really tricky. You can see the various models online for sale, often with metal, and it often has the Galilean moons, plus our own moon, and it's good, except the scale again makes the pieces really small and thus not great for crowds OR way too large to transport. 


One thing some people do is do balls of varying size if they're in a large room, and they get someone to be the sun, and someone to be each of the planets, and maybe some to be moons, and get them to stand in the spot they would be if everything was to scale. 


Another "action" that some people do is a planetary puzzle, say for Jupiter, where they have to put all the pieces in place PLUS there are spots for various moons to go around it. Often numbered to not make it TOO difficult, even the young can do it. Maybe 20 pieces for the planet, or 30 perhaps, plus some surrounding moons.


One other thing to consider -- if they're doing a bunch of stuff with the moon, for example, print a bunch of small "moon discs", that they can take with them as souvenirs. Some people print 3D discs and print on label paper to allow "stick ons" so you don't have to paint or use multi colours.


Others more creative than I hopefully have bigger suggestions. Those are some things I've seen that seemed to work well...



#3 SporadicGazer


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Posted 09 December 2023 - 12:53 PM

The problem is the scale.  To show the orbits the Sun & Planets have to be of exaggerated size to see.  To show any details they need to be much too close together, or isolated.  I don't have a solution, other than divide and conquer.


For Solar eclipses the Sun, Earth, and Moon relationship needs to be shown.  This is somewhat difficult because they don't orbit in the same plane.  (Which is also why it's interesting, e,g, with eclipses only in spring & fall when the orbits intersect.)


For accurate demonstration of the true scale, the exercise in Guy Ottewell's "The Thousand Yard Model:  Or, the Earth as a Peppercorn" book is wonderful.  But it doesn't show any of the orbital interactions, e.g. eclipses, or moons.  Plus it is an activity not a display you could have at an outreach event.


I like the illustration of the texture suggestions, but don't really see them as more than a another piece.


Good luck!  Interesting thought problem though.


#4 Starry_Spruce


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Posted 10 December 2023 - 12:44 PM

Thanks for these thoughts.


Yes scale is definitely an issue. What I didn't mention was that my initial idea was to do an installation akin to the Guy Ottewell exercise. This would be on a piece of conservation land open to the public, so the scaled planets would be placed at scaled distance along a trail and/or field and left there for some time. People would visit at their leisure.


I was considering trying to add another element to 'bring it home' with either the armillary sphere type concept or alternatively a model that helps demonstrate solstices/equinoxes (less concerned about eclipses for this). I agree this type of model would not work at proper scale.


I might have to decide what the focus should be and whether either of these additions would be useful. Some sort of armillary sphere / celestial sphere / sun dial type device is still the best I can think of for helping bridge the concept of earth's movement around the sun to the reality of the observed sky. E.g. why does the ecliptic change altitude seasonally but the celestial sphere stays constant (albeit with the sun in a different location and therefore changing the solar time at which the stars are visible).


With a globe that is oriented with one's specific latitude oriented 'up' and with the axis of rotation pointing towards Polaris, I hope it drives home the point that north is not up! I think that maps hanging on walls with north oriented 'up' has led people to subconsciously think that north is 'up.' And that a simplistic solar system model has some sort of 'up.' 


If going with an armillary sphere concept, I think it would need to be simplified and better symbolized/defined for the uninitiated. I would consider leaving off the tropic of Cancer/Capricorn and the Artic/Antarctic circles and focus on the horizon line, the celestial equator, the axis of rotation, the meridian, and the ecliptic and the sun's movement along the zodiac. Giving these items some contrast (as opposed to all brass) and labels I think might help. 

#5 Starry_Spruce


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Posted 12 December 2023 - 08:52 PM

"e,g, with eclipses only in spring & fall when the orbits intersect."


I'm just revisiting this after wondering about it. It hadn't occurred to me that this was the case, but I thought it made some sense. It appears, however, that the 'nodes' (the intersection of the lunar orbital plane and the ecliptic) rotate and are not always near the equinoxes.


Edited by Starry_Spruce, 13 December 2023 - 08:18 AM.

#6 KBHornblower



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Posted 13 December 2023 - 02:10 PM

Starry Spruce, you are correct.  The Moon's orbital intersection precesses westbound and makes a complete cycle in about 18.6 years.  It is not fixed at the equinoxes.  Eclipses can happen at any time of the year.

#7 Freezout


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Posted 29 December 2023 - 03:06 PM

I built this for outreach at a school, mostly to show why we see phases on the Moon and always the same face.
The Earth turns on itself but the stick stays in place. The stick of the Moon can be moved to pre-drilled holes (for the different phases). The Moon can turn on its axe.
The Sun will be figured by a low power reading lamp. The plate with the spheres has to be moved to figure the seasons.







Edited by Freezout, 29 December 2023 - 03:17 PM.

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#8 No N in collimation

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Posted 16 January 2024 - 12:30 AM

Not one of these?



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