Our knowledge of the universe derives primarily from telescopes. Telescopes allow us to see deeper into the universe than we can with the naked eye.
There are a few factors that directly play into this question: the altitude at which an observatory is located, as well as the size of the mirror.
Fermi Gamma - Ray Space Telescope (GLAST) - By collecting gamma rays, GLAST can learn more about supermassive black holes, neutron stars, and quasars. Launched in 2008, GLAST is still operational today.
Spitzer Space Telescope - This telescope has allowed scientists to see regions of space that optical telescopes are unable to see. Spitzer was placed in an orbit different from other telescopes.
Keck Telescope - Built-in 1992 (Keck 1) and 1996 (Keck 2), with a mirror 32.8-feet (10-meters) in diameter, this telescope has a larger mirror than some of the most powerful telescopes in the world.
Hubble Space Telescope - Launched in 1990, the Hubble Space Telescope gave the public never before seen images of the wonders of space.
James Webb Space Telescope - The James Webb Space Telescope (JWST) is one of the most powerful telescopes ever built. It is the successor to the famous Hubble telescope, and it is significantly more powerful.