The Hubble Space Telescope (HST) is a multi-instrument observatory that has dramatically changed humanity's understanding of the universe for over two decades, with dramatic images of stars, planets, and galaxies. Hubble orbits Earth; its position above the atmosphere, which distorts and reduces the light that reaches the surface, gives it a view of the universe that typically surpasses that of ground-based telescopes. HST's various instruments investigate the universe in the visible, ultraviolet, and infrared portions of the spectrum. HST was deployed from the space shuttle Discovery on April 25, 1990. After that, the telescope underwent five servicing missions to repair or upgrade various instruments and systems.