Kepler's Triangle is a right triangle whose sides are in geometric progression. This concept is named after the German mathematician and astronomer Johannes Kepler. The sides of the triangle are related to each other in such a way that they reflect the mathematical relationship known as the "golden ratio."

Johannes Kepler recognized the image by saying that geometry has two great treasures, one of which was the Pythagorean theorem and the other the golden ratio, as shown above. The first is like a pile of gold, the latter like a precious gem.