Above all scientific projects, the Hubble Space Telescope encapsulates and recapitulates the human yearning to explore distant worlds, and understand our origins and place in the universe. Its light grasp is 10 billion times better than Galileo’s best spyglass, and many innovations were needed for it to be realized: complex yet reliable instruments, the ability for astronauts to service the tele­scope,1 and the infrastructure to support the projects of thousands of scientists from around the world. The facility and its supporters experienced failure and heartache as well as eventual success and vindication.

Hubble’s legacy has touched every area of astronomy, from the Solar System to the most distant galaxies. In the public eye, it’s so well known that many people think it’s the only world-class astronomy facility. In fact, it operates in a highly competitive land­scape with other space facilities and much larger telescopes on the ground. Although it doesn’t own any field of astronomy, it has made major contributions to all of them. It has contributed to Solar System astronomy and the characterization of exoplanets, it has viewed star birth and death in unprecedented detail, it has paid homage to its namesake with spectacular images of galaxies near and far, and it has cemented important quantities in cosmology, including the size, age, and expansion rate of the universe.2

Ranked by size of the mirror, Hubble wouldn’t make it into the top fifty largest optical telescopes.3 Its preeminence is based on three factors associated with its location in Earth orbit. The first

is liberation from the blurring and obscuring effects of the Earth’s atmosphere. Ground-based telescopes typically make images far larger than their optics would allow because turbulent motion in the upper atmosphere jumbles the light and smears out the im­ages. Hubble gains in the sharpness of its vision by a factor of ten relative to a similar-sized telescope on the ground. Earth orbit also provides a much darker sky, which affects the contrast and depth of an image. The difference you might see in going from a city cen­ter to a rural or mountain setting is only part of the story; natural airglow and light pollution affect even the darkest terrestrial skies. A vacuum can’t obfuscate. The last feature of a telescope in Earth orbit is its ability to gather wavelengths of radiation that would be partially absorbed or even quenched by the Earth’s atmosphere. Hubble has taken advantage of this by working at infrared and ultraviolet wavelengths.

The Hubble Space Telescope (HST) is well into its third decade of operations, and it’s easy to take for granted the beautiful images that are released almost weekly. But it was not an effortless jour­ney for NASA’s flagship mission.

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