I am inclined to agree with Professor Michael Crowe (*), now emeritus at Notre Dame, that it is difficult to directly associate the illustrious German mathematician Carl Friedrich Gauss (30 April 1777 – 23 February 1855) with the notion of sculpting an enormous illustration of the Pythagorean theorem as a way to communicate with inhabitants of the Moon, Venus or Mars. The closest Venus gets to Earth is 38 million kilometers (24 million miles), while the closest Mars has gotten to Earth recently was in 2003 – 56 million kilometers or about 35 million miles. So any lunar inhabitants viewing from the sunlit side (facing us) of the moon would have had a much easier time in terms of distance.
The idea was to sculpt the sides of the triangle with rows of pine trees and cover the areas inside the triangle and the squares with wheat. One proposal was to locate it in Siberia, but it would seem like snow would mask the design from observers for months at a time. If the sides were to be hundreds of miles long some army is managing 1200 miles of pine trees and 560,000 square miles of wheat.
(*) his book on this aspect of the history of science was first published in 1986 by Cambridge University Press with the title The Extraterrestrial Life Debate, 1750-1900. My copy is from Dover Publications. On interest here are pages 205–207.