What’s the logo?

abul_heptagon_small

The main logo for the site is shown above, and it’s my current personal favorite geometric construction.  This comes from Abu’l Wafa, a 10th century Persian geometer, and gives a quick-and-easy method of constructing a nearly regular heptagon:

  • Let ABC be an equilateral triangle inscribed in a circle.
  • Bisect BC at D.
  • CD is very nearly the side of a regular heptagon inscribed in the circle.

How close is it?  The green shows what happens when you mark six sides, equal in length to CD, with the seventh side joining the last vertex to your starting point.  The blue is a regular heptagon.  They’re almost indistinguishable.  (The inset shows that the true regular heptagon does deviate very slightly from the approximate regular heptagon)

I actually used this a few years ago, to set up a seven-sided tomato cage.  I’ll leave the details as an exercise for the reader…

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