A collection of Hubble Space Telescope images shows distant supernovas, the death explosions of massive stars. The top photos show each region before the explosion. The bottom row shows the explosions’ aftermaths

　　According to NASA, "Hubble played a key role in discovering that a mysterious form of energy called dark energy is acting like a cosmic gas pedal, accelerating the universe’s expansion rate. Dark energy shoves galaxies away from each other at ever-increasing speeds and works in opposition to gravity." Hubble’s observations of supernovas helped reveal that the mysterious energy is a constant presence in the universe.

　　According to NASA, "One of Hubble’s key duties was to help astronomers determine a precise age for the universe. The telescope helped astronomers accomplish that goal, narrowing the universe’s age to 13 to 14 billion years old, an accuracy of about 10 percent. Astronomers made observations of Cepheid variable stars [pictured above]—pulsating stars used to measure vast distances—in the Virgo and other clusters to establish the expansion rate and the universe’s age."

　　According to NASA, "Hubble provided astronomers with a ’scrapbook’ full of snapshots of the early universe ...[including] pictures of the ’deep’ universe in a series of unique observations: the Hubble Deep Fields, the Great Observatories Origins Deep Survey, and the Hubble Ultra Deep Field [pictured above]. The observations provided the deepest views of the cosmos in visible, ultraviolet, and near-infrared light."

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