This is a beautiful sheet of 6 stamps, issued in 2000 by the United States titled Probing the Vastness of Space. It features the Hubble Space Telescope, a Radio Inteferometer in New Mexico, telescopes from the Keck Observatory in Hawaii, the Cerro Tololo Observatory in Chile, the Mount Wilson Observatory in California, and the Arecibo Observatory in Puerto Rico. The sheet is Scott catalog #3409.