### The starburst icosahedron with long bars

Posted:

**Sun Dec 27, 2009 2:13 am**How did those guys at Geomag come up with the new bar length? Here's one possibility - first let's

take some careful measurements:

So, the geometric length turns out to be: 69.94mm

Now, a double-length Geomag original bar has geometric length: 65.78mm

and the ratio between these two numbers is: 0.94 - remember that!

Look in wikipedia to get the circumradius of the icosahedron

http://en.wikipedia.org/wiki/Icosahedron

it's 1/4sqrt(10+2*sqrt(5)) = 0.95106

Coincidence? maybe.

Some calculations give away that a double-length Geomag classic rod is

just 0.74mm short of the required length to act as the radius element

for a starburst icosahedron. And 0.8mm is 1/32" which is just the size of

some little magnetic shims I happen to have handy.

Here's a detail of 12 rods arranged around a ball with icosahedral symmetry.

Should you wish to try this at home, you can manufacture shims easily by

using a hole-punch on one of those magnetic stickers you probably have on the fridge: the

disks ejected by the hole punch are just the right size for Geomag bars.

Here's an example: http://www.flickr.com/photos/karlhorton/404972512/in/set-72157594564548492/

take some careful measurements:

So, the geometric length turns out to be: 69.94mm

Now, a double-length Geomag original bar has geometric length: 65.78mm

and the ratio between these two numbers is: 0.94 - remember that!

Look in wikipedia to get the circumradius of the icosahedron

http://en.wikipedia.org/wiki/Icosahedron

it's 1/4sqrt(10+2*sqrt(5)) = 0.95106

Coincidence? maybe.

Some calculations give away that a double-length Geomag classic rod is

just 0.74mm short of the required length to act as the radius element

for a starburst icosahedron. And 0.8mm is 1/32" which is just the size of

some little magnetic shims I happen to have handy.

Here's a detail of 12 rods arranged around a ball with icosahedral symmetry.

Should you wish to try this at home, you can manufacture shims easily by

using a hole-punch on one of those magnetic stickers you probably have on the fridge: the

disks ejected by the hole punch are just the right size for Geomag bars.

Here's an example: http://www.flickr.com/photos/karlhorton/404972512/in/set-72157594564548492/