We learn in school that the measures of the interior angles of a triangle add up to 180 degrees. Did you know that triangles on surfaces other than planes can have different sums? The interior angles of a triangle on a sphere add up to more than 180 degrees, and the interior angles of a triangle on a pseudosphere add up to less than 180 degrees. Why would anyone care? Well, a triangle on a plane is a good study when doing calculations on a local area on the ground, such as what surveyors do. Triangles on a sphere (elliptical geometry) give part of the picture of what is happening on our big ball of a planet. Triangles on a pseudosphere (hyperbolic geometry) give part of the picture of what is happening to particles traveling in space. It’s all relative, m’dear!