An Eye in the Sky - Why Are There Telescopes in Space?

The Hubble Telescope, a high-tech telescope in space.

Ever since Galileo pointed his telescope to the sky in 1609, telescopes have slowly revealed the universe to us. Over time, the telescopes got better, and so did the views they provided. But we started to hit a point of diminishing returns. As powerful as telescopes were getting, factors that seemed inescapable on Earth got more and more in the way. There was one clear solution: make a telescope that’s not on Earth.

The Space Telescope Advantage

A space telescope is exactly that: a telescope in space. It may seem superfluous to launch an entire telescope into space, but there are actually a lot of advantages when compared to a ground-based telescope.

Telescopes on Earth have to compete with the Earth’s atmosphere. Air may look transparent to us, but when trying to peer through 62 miles of it, the slightest bits of distortion it causes add up. This is the reason stars twinkle at night. If you stare long enough at a star, you’ll notice how it seems to brighten and dim, while subtly shifting position. This is due to distortions caused by the atmosphere as the star’s light passes through. Scientifically, this is known as scintillation. It may look pretty to us, but it makes it more difficult to get a clear image through a telescope, especially when the telescope’s magnification exaggerates the distortions. A telescope positioned in space has no atmosphere to peer through, leaving it looking at crisp, sharp, and steady views of the stars and other objects.

Another big advantage of a space telescope is that it can observe any time, night or day, giving it twice the observation time of an Earth-based telescope. Similarly, a space telescope doesn’t have to contend with the light pollution that is prominent across much of Earth’s surface.

How Space Telescopes Work

For the most part, space telescopes work the same as traditional telescopes. However, even beyond Earth’s atmosphere, just an ordinary telescope, no matter how big, doesn’t have enough power to capture the stunning images we get from telescopes like Hubble. Instead, space telescopes act as an extremely powerful long-exposure camera attached to a powerful telescope.

In photography, if you want to take a clear picture at night, you need to keep the shutter of the camera open longer to gather more light. The more light gathered, the brighter the resulting image will be, allowing shapes and colors to be seen clearly, even in a picture taken at night. Space telescopes operate on the same principle. They behave like massive buckets of light that take every photon they can from their target over an extended period of time. This light is all collected and added together. The longer the exposure, the more light gathered and the brighter and clearer the resulting image.

Meet the Space Telescopes

While the two space telescopes you’ll hear about most are the Hubble and James Webb Space Telescopes, there are plenty of others as well. The first one ever launched was the Orbiting Astronomy Observatory (OAO-1) in 1966. While it failed just three days after launch, it was replaced two years later by the OAO-2. Other prominent space telescopes include the Chandra X-Ray Observatory, Spitzer, and Kepler.

A view of the same portion of the center of the Milky Way in three different spectra by three different space telescopes.

Each telescope has its own specialty. The Hubble Telescope was designed to see visible light, the light that humans can see, while Chandra was designed to see X-rays and Spitzer and Webb to see infrared. This is another advantage to space telescopes. Humans are only able to see a small portion of the entire light spectrum—about 0.0035% of it. Part of the reason our eyes developed to see what they see is that the atmosphere blocks out much of the rest of the spectrum, making X-ray or infrared astronomy difficult on Earth. But in space, telescopes can see these other types of light clearly, giving us a whole new vantage point to the universe.

The result when you combine all three of the previous views into one image. A far more complete picture of the Milky Way than what's possible with one telescope.

In addition to other spectra, space telescopes can also be designed for specific missions. The Kepler Space Telescope was designed specifically to hunt exoplanets, planets around other stars, and had great success in its mission.

Coming next in the world of space telescopes is the Nancy Grace Roman Telescope, which is currently planned to launch on August 30, 2026. The Roman Telescope will boast a field of view over 100 times larger than Hubble’s with the same resolution, meaning that it will be able to see far more at once than its predecessor. Its goals include hunting for exoplanets and studying the structure of the universe to learn more about dark energy.

Space telescopes have been our ultimate tool in understanding the universe and discovering its secrets. With them, we’ve peered deeper into the universe than ever would have been possible stuck here on Earth.