Why Have a Telescope in Space?

Hubble's unique characteristics – like its broad wavelength coverage, its position beyond Earth's atmosphere, and its assortment of science instruments – have made it one of astronomy's most important tools.

Quick Facts

Why a Space Telescope
NGC 3147 is a spiral galaxy 130 million light-years away from Earth. Hubble’s clear view of the cosmos enables it to capture details like the clusters of young blue stars, pinkish nebulae and lanes of dust visible in the galaxy’s graceful, winding arms. Due to the blurring effects of Earth's atmosphere, ground-based telescopes are unable to achieve such resolution.
NASA, ESA, S. Bianchi (Università degli Studi Roma Tre University), A. Laor (Technion-Israel Institute of Technology), and M. Chiaberge (ESA, STScI, and JHU)

Hubble was designed as a general purpose observatory, meant to explore the universe in visible, ultraviolet, and infrared wavelengths. To date, the telescope has studied a vast array of cosmic objects, providing views that astronomers were unable to capture from the ground.

In addition to blocking certain wavelengths of light altogether, Earth’s atmosphere is made up of shifting pockets of air that cause the twinkling appearance of stars in the night sky. This motion blurs images captured by telescopes on the ground. Hubble was placed into orbit above the atmosphere to avoid these effects.

As the telescope orbits Earth, its mirror gathers light from the cosmos, collecting images and data. For some of deepest images, the telescope has stared at the same point in the sky for days to capture the dim glow of the distant universe.

Hubble Space Telescope in orbit
The Hubble Space Telescope floats against the background of space on May 19, 2009, after being released by the space shuttle Atlantis following the repairs and upgrades of Servicing Mission 4. Above the Earth's atmosphere, Hubble is more powerful than any ground-based telescope.

Hubble Advantages



When you look up at the stars in the sky, they seem to twinkle. That’s because shifting pockets of air in Earth’s atmosphere distort your view, even on the clearest nights. When astronomers try to take a picture of a cosmic object from the ground, that picture ends up blurry. Hubble’s position above the atmosphere lets it observe steady, unwavering light from cosmic objects and thus achieve higher resolution.

Hubble floating above Earth
Hubble has been in low-Earth orbit since 1990, approximately 326 miles (525 km) above the surface. This vantage point above the atmosphere gives Hubble the ability to take breathtaking images not available from the ground.


More Wavelengths

Earth’s atmosphere stops certain wavelengths of light. This is good for life on our planet, since it keeps away some dangerous radiation, but it also blinds us to some of the light emitted by cosmic objects. Hubble is designed to view some ultraviolet and infrared wavelengths, which are blocked or partially blocked by the atmosphere, as well as visible light. Hubble’s perceptiveness to this broad range of wavelengths captures details that would otherwise be invisible, revealing a wealth of information about cosmic objects.

A detailed image of the crab nebula.
The Crab Nebula is imaged here in numerous wavelengths. Red is radio waves from the ground-based Very Large Array observatory; yellow is infrared light taken by the Spitzer Space Telescope; green is visible light that your eyes can see, captured by the Hubble Space Telescope; blue represents ultraviolet light imaged with the XMM-Newton observatory; and purple are x-rays captured by the Chandra X-Ray Observatory.
NASAESA, G. Dubner (IAFE, CONICET-University of Buenos Aires) et al.; A. Loll et al.; T. Temim et al.; F. Seward et al.; VLA/NRAO/AUI/NSF; Chandra/CXC; Spitzer/JPL-Caltech; XMM-Newton/ESA; and Hubble/STScI



Hubble has extremely high angular resolution, or ability to distinguish between two objects that are very close together. If your eyes had Hubble’s resolution, you could read the date on a dime two miles away. For Hubble, this means it can see fine details in star-forming nebulae, galaxies, and other cosmic objects.

Caldwell 33 and 34
This image of Caldwell 33 and 34, known collectively as the Veil Nebula, demonstrates Hubble's high resolution but small field of view. The large image was taken by a ground-based telescope, while the three insets are Hubble close-up views, demonstrating the increased resolution that Hubble can deliver.
NASA, ESA, the Hubble Heritage (STScI/AURA)-ESA/Hubble Collaboration, and the Digitized Sky Survey 2. Acknowledgment: J. Hester (Arizona State University) and Davide De Martin (ESA/Hubble)


Dark Skies

Orbiting 320 miles (515 km) above the surface, Hubble doesn’t have to contend with any form of light pollution or weather conditions. This gives it a permanent, clear dark sky, which, combined with its sharp vision, allows it to see objects 10 times fainter than those that can be observed from Earth even by the largest telescopes.

An late evening image of Los Angeles showcasing the many lights around the area
Los Angeles sparkles at night but is an example of light pollution that affects astronomical images and data.
NASA / J. Jeletic



Hubble was positioned just above Earth’s atmosphere, in what’s called a low-Earth orbit, so it would be unaffected by Earth’s atmosphere. That position only hundreds of miles above the surface also meant that Hubble could be repaired and upgraded by astronauts, enabling the repair of its original mirror flaw, keeping the telescope in orbit for more than three decades and continuously renewing it with the newest technology.

Two astronauts in white space suits tethered on an arm servicing the Hubble Space Telescope in space.
Astronauts John Grunsfeld and Andrew Feustel work to remove and replace the Hubble Space Telescope's Fine Guidance Sensor 2 during Servicing Mission 4. Hubble was designed and built with such servicing in mind.



Hubble has multiple science instruments dedicated to probing the universe in unique ways. Hubble’s cameras observe the universe in a variety of wavelengths, including those invisible to the human eye. Its spectrometers dissect light into its component colors, exposing details like chemical composition and temperature. Its interferometers are used for aiming the telescope but can also measure the relative positions and brightnesses of stars.

Hubble's Cosmic Origins Spectrograph (COS) instrument allows Hubble to probe the characteristics of an astronomical object. Hubble is equipped with numerous cameras, spectrometers, and interferometers.