- NASA’s Hubble Space Telescope, launched in 1990, is a multipurpose observatory in Earth orbit used for astrophysics and planetary science.
- Hubble has revolutionized our understanding of the cosmos large and small. It studies asteroids and planets in our own solar system, exoplanets and clouds of gas where stars are born, and the very fabric of the universe itself.
- You can cheer on Hubble by sharing images from the telescope and following the progress of its successor, the James Webb Space Telescope.
Why do we need the Hubble Space Telescope?
A tiny patch of space that contains thousands of galaxies. A stunning peek inside a cloud of dust and gas that reveals baby star systems. Crisp views of the outer planets, year after year. Pictures like these are only possible from a telescope above our planet’s atmosphere, where NASA’s Hubble Space Telescope has been studying the cosmos from Earth orbit for more than 30 years.
Earth’s atmosphere distorts the light from celestial objects, causing them to twinkle. Although ground-based telescopes can correct for this using a technology called adaptive optics, our atmosphere also blocks many wavelengths of light that are helpful to study the cosmos, including infrared and ultraviolet.
Baby stars and planets often lie behind clouds of gas and dust that absorb visible light, but these objects shine through in the infrared, allowing Hubble to see them. To the naked eye, many hot, young stars blend into the glow of nearby galaxies, but Hubble can pick them out in ultraviolet light, helping scientists understand how stars and galaxies evolve.
The Planetary Society is committed to increasing discoveries about the worlds of our solar system and beyond. Learn more about the world's current and future space missions, and find out how you can get involved.
How do telescopes allow us to see back in time?
The farther away cosmic objects are, the longer it takes their light to reach us. Sunlight hitting the Earth is actually 8 minutes old by the time it reaches us. Light from the nearby Andromeda galaxy is more than 2.5 million years old. By looking at extremely distant objects, scientists learn more about what the universe was like in its early days. It’s even possible to see the afterglow of the Big Bang itself!
Although Hubble was not the first space telescope, it was the most ambitious: the first of NASA’s 4 “Great Observatories” launched between 1990 and 2003. Astronomer Lyman Spitzer wrote about the potential of large space telescopes in 1946, and Nancy Grace Roman, NASA’s first chief astronomer, helped the idea come to fruition thanks to her tireless lobbying efforts. She is often referred to as the mother of Hubble, and the Roman Space Telescope, set to launch in the mid-2020s, is named after her in recognition.
Data from Hubble have revolutionized our understanding of the cosmos. We now know the universe is roughly 13.8 billion years old. We can make more accurate estimations of its expansion rate: 74 kilometers (46 miles) per second, per megaparsec. (For comparison, the Andromeda Galaxy lies just under 1 megaparsec away.) We think there are about 2 trillion galaxies in the universe—that’s galaxies, not stars. When you consider that the Milky Way, a rather average galaxy, contains 100 to 400 billion stars, you start to get an idea of just how enormous the cosmos really is.
Hubble has helped us see stars being born. It has imaged shock waves around other stars traveling through the cosmos, and directly imaged planets orbiting other stars. Closer to home, Hubble caught comet Shoemaker-Levy 9 colliding with Jupiter in 1994. It has watched comets and asteroids break apart. Hubble’s Outer Planets Atmospheres Legacy program, OPAL, monitors the outer planets to show us how their atmospheres change over time.
Hubble is much more than a NASA project. The European Space Agency (ESA) provided one of the telescope’s cameras and the solar arrays that give it power. A team of ESA scientists also work at the Space Telescope Science Institute (STScI) at Johns Hopkins University in Baltimore, Maryland, which operates the telescope. These contributions entitle European astronomers 15% of Hubble’s observing time.
How Hubble works
Hubble orbits Earth at an altitude of roughly 570 kilometers (350 miles). At its core, Hubble is a 13-meter-long tube (43 feet) opened to space on one end. Light travels through the tube to a bowl-shaped, 2.4-meter-wide (94.5-inch) main mirror and bounces up to a secondary mirror. That mirror concentrates the light into a beam the size of a dinner plate, which travels back through a hole in the middle of the primary mirror. From there, the light is directed through various science instruments for analysis.
Bias in science
In theory, anyone on Earth can use Hubble by applying for time through STScI. However, a 2014 study of Hubble time allocations found that only 18% of proposals from women were accepted, as opposed to 24% from men. NASA changed the application process so that neither proposers nor reviewers know each others’ identities or institutions. An initial test showed more equitable acceptance rates: 8.7% of womens’ and 8% of mens’ proposals were accepted.
Space Shuttle Discovery launched Hubble in 1990. The telescope was designed to be repaired and upgraded over time via subsequent shuttle visits, a feature that immediately came in handy when Hubble’s first images came back to Earth blurry. NASA later determined that the telescope’s edges were polished slightly too flat—just one-fiftieth the thickness of a human hair—rendering Hubble near-sighted. Since replacing the mirror was not practical, engineers constructed a phone-booth-sized mirror package that was installed inside the telescope in 1993 by astronauts aboard Space Shuttle Columbia.
Astronauts ended up visiting Hubble 4 more times:
- 1997: During an 11-day mission, Space Shuttle Discovery astronauts installed new instruments, extending Hubble’s vision into the near-infrared, a wavelength of light that allows scientists to study the early universe.
- 1999: What was originally planned as a maintenance visit turned into a repair mission after the fourth of Hubble’s 6 gyroscopes failed. These devices orient and point the telescope. Astronauts aboard Discovery replaced all 6 gyroscopes and made a number of other upgrades and repairs.
- 2002: Columbia astronauts install a new camera that allows Hubble to see wavelengths ranging from visible to far-ultraviolet. The crew also replaced the observatory’s solar arrays.
- 2009: This final mission to Hubble was for a time cancelled after the loss of Columbia in 2003, which claimed the lives of all 7 crewmembers. NASA greenlit the mission after devising an elaborate rescue plan in the event Space Shuttle Atlantis was damaged during launch. During a 13-day mission, astronauts used 5 spacewalks to repair and upgrade much of the telescope, ensuring it will remain operational for at least some time after NASA’s James Webb Space Telescope launches.
A smooth mirror
If Hubble’s mirror was scaled up to the width of the North American continent, the highest hill or lowest valley would only be a few inches from the surface!
How you can support Hubble
NASA originally expected Hubble to last 15 years, thanks to maintenance visits from the Space Shuttle. Now in its fourth decade of operations, the observatory has far exceeded its life estimates and shows no signs of slowing down. It is expected to continue operating even after the James Webb Space Telescope launches in 2021.
You can cheer on Hubble by sharing stunning images from the telescope and following the progress of Webb, which will complement and extend the work of Hubble. Sign up for our weekly newsletter, The Downlink, to receive mission updates and get tools to learn, share, and advocate for more space exploration.
Want to get involved even more? Visit our action center to learn how to take action with your government and in your local community.
Acknowledgements: This page was initially written by Jordan Strickler and is regularly updated by Planetary Society staff writers.