What is it? - again

  • Thread starter Evo
  • Start date
  • #76
67
0
turbo-1 said:
Ah yes, it looks like a lightbulb in an explosion-proof housing. Operating room?

Close enough! It's a shot of the glass globe that covered the light bulb above the stairs in our old home. The picture was taken under the globe while looking straight up.
I'm not sure if it was explosion-proof (it came with the house).

-GeoMike-
 
  • #77
Mk
1,984
3
GeoMike said:
I'm not sure if it was explosion-proof (it came with the house).
:rofl: Ha ha, :rofl:
 
  • #79
Evo
Mentor
23,192
2,996
No one has guessed this yet. Although Gokul was very close.

twisting_Edge said:
This one should be pretty easy for anyone with an interest in abstract geometry. You have to get the precise figure, though.
solo.jpg

Obviously, it's a construct sitting on top of my computer.
 
  • #80
695
6
Is it the trajectory of the "magic" bullet? that killed kennedy?
 
  • #81
6,265
1,280
The child that resulted from a mating of M.C. Escher and R. Buckminster Fuller?
 
  • #82
DaveC426913
Gold Member
19,371
2,870
Evo said:
No one has guessed this yet. Although Gokul was very close.


solo.jpg
I got it! It's a dodecahedron extended into a star.

How I figured it out: Count the struts in each vertex: each has five. That means each vertex has a pentagonal cross-section. If you cut off the tips, you get all pentagons.

(And now that I know that, I can see that it also has 12 points, which is how many faces a ddh'n has.)

Been trying to find a proper name for it. Would that be a "stellated" dodecahedron?
 

Attachments

  • PF060910dodecahedron.jpg
    PF060910dodecahedron.jpg
    14.1 KB · Views: 366
Last edited:
  • #83
Evo
Mentor
23,192
2,996
DaveC426913 said:
I got it! It's a dodecahedron extended into a star.

Every vertex has five struts. Thus, if you trace the 5 of each vertex back to a face, you get one face of a dodecahedron.

(And now that I know that, I can see that it also has 12 points, which is how many faces a ddh'n has)
Yes!!, it is a dodecahedron!!!! Dave, you're awesome. :approve:

It's actually a lesser stellated dodechahedron
 
Last edited:
  • #84
6,265
1,280
Last edited:
  • #85
Evo
Mentor
23,192
2,996
Here is his e-mail to me.

The icosahedron is one of the Platonic solids. It is almost identical
to
the lesser stellated dodecahedron (the figure I posted, which is NOT a
Platonic solid), because they both have the same number of vertices,
and
the same number of edges.

Basically, if you look at the icosahedron, you see a pentagon under
each of
the points. Beyond that is another pentagon in a parallel plane, then
the
last of the 12 points. If you take each edge leading from the central
point
to the second pentagon, not the first, and do that for all the points,
you
get the lesser stellated dodecahedron. Of course, once you've done
that to
all the points, each of the pentagons becomes a pentacle. The lesser
stellated dodecahedron is to the icosahedron exactly as a pentacle is
to a
pentagon.

I have other photos showing that aspect of the lesser stellated
duodecahedron much more clearly. Clarity was not the goal in this case.

Platonic solids are cool. They are very limited (there's only five),
but
they are very neat things.
 
  • #86
DaveC426913
Gold Member
19,371
2,870
I was trying to figure out how to describe regular polyhedrons without getting long-winded and I've managed to find it in Wiki. It's the "vertex configuration". It is the number of polygons around each vertex and what polygon they are.

There are five known:
3.3.3 (tetrahedron)
4.4.4 (cube)
3.3.3.3 (octohedron)
5.5.5 (dodecahedron)
3.3.3.3.3 (icosahedron)
There can't be any less than 3 polygons per vertex because you get degenerate objects, eg.: 3.3 (a 2D flat triangle)
And most configurations have an upper limit or you get a tiled plane: 4.4.4.4 (4x90degrees=360 - a flat plane)

So there are very clear bounds on the regular solids. Ah what what about interpolation??? Has every combination of polygons vs. sides been represented? No! There's one left.

4.4.4.4.4

It is neither degenerate nor a tiled plane. And it does form a closed shape (eventually). But it bends just one platonic solid rule: it's not convex.

Sorry, I'm hijacking this thread.
 
Last edited:
  • #87
695
6
I haven't had 5 platonic relationships in my life. are you sure you added right?
 
  • #88
DaveC426913
Gold Member
19,371
2,870
tribdog said:
I haven't had 5 platonic relationships in my life. are you sure you added right?
Ba DUM bum!
 
  • #89
1,414
5
tribdog said:
I haven't had 5 platonic relationships in my life. are you sure you added right?


Its ok, I'm sure the lurkers thought it was funny.

Are you campaigning all of a sudden for that ribbon?
 
  • #90
Evo
Mentor
23,192
2,996
Aha, tribdog might be eligible if he hangs around long enough.
 
  • #91
695
6
If you're asking I'm always eligible, baby.
 

Related Threads on What is it? - again

  • Last Post
Replies
22
Views
7K
Replies
37
Views
4K
  • Last Post
Replies
14
Views
782
  • Last Post
Replies
6
Views
2K
  • Last Post
Replies
11
Views
2K
  • Last Post
Replies
3
Views
2K
  • Last Post
4
Replies
89
Views
17K
  • Last Post
7
Replies
153
Views
9K
  • Last Post
Replies
6
Views
3K
Top