Paul Yiu's Introduction to the Geometry of the Triangle and other works
Jean-Louis Ayme's Geometry * Géométrie * Geometria
Bernard Gibert's Cubics in the Triangle Plane
Quim Castellsaguer's The Triangles Web
Triangle Geometry at MathWorld
Homepage Floor van Lamoen
Triangle Centers with C.a.R.
Grinberg at MathWorld
Moses at MathWorld
Index of Biographies of Mathematicians
The Geometer's Sketchpad
Journals that publish triangle geometry
Journal for Geometry and Graphics
American Mathematical Monthly
Triangle Geometry Interest Group
Date: Wed, 22 Dec 1999
From: "Antreas P. Hatzipolakis"
Subject: Hyacinthos Mailing List
I just created a mailing list devoted to Triangle Geometry.
The name of the list is Hyacinthos
(in honor of
Emile Michel Hyacinthe Lemoine).
By 7 March 2013, the number of messages had passed 21,600.
To subscribe, visit
The clustering of triangle centers into families has been compared to constellations of stars, and this fact has prompted the naming of certain points after stars. For a list of such names with astronomical data, visit
SkyEye - (Un)Common Star Names
The Keepers of SkyEye, Lynne Marie Stockman and David Harper, wrote to the Keeper of ETC that there are two constellation names of particular interest:
The alpha star in Triangulum is sometimes called Mothallah. According to Richard Hinckley Allen in Star Names: Their Lore and Meaning (originally published in 1899 and then first republished by Dover in 1963), the constellation name was translated by Arab astronomers as Almutallath, Almutaleh, Almutlato, Mutlat, etc. He goes on to say that the constellation was known as Shalish to the Jews, from the name of a triangular-shaped musical instrument. The Romans knew the constellation as Deltotum, and it has had various other names over the centuries: Aegyptus, Nilus (both after the Nile delta of Egypt), Trigonum, Trigonus, etc. The alpha star in Triangulum Australe is called Atria.
Contact the Keeper
Your suggestions for improving ETC are welcome, as are submissions of new centers (and bicentric pairs) for possible inclusion in ETC. To submit such a center, send the simplest trilinear coordinates you can find, expressed as functions of sidelengths a,b,c or vertex angles A,B,C, or both. Also send, in quotable wording, geometric information about the center. Of course, before sending, you should evaluate your center at the triangle (a,b,c) = (6,9,13) and apply the Search option to see if your center is already listed. (Even if it is, perhaps you have information that should be added to ETC.)
Clark Kimberling (University of Evansville)
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