As a human being, every time I see a new jaw-droppingly gorgeous astronomical image, I’m staggered by the beauty of the cosmos.
But as an astronomer who’s been observing the universe his whole life, when I see these images, I’m amazed at how far we’ve come in that time, technologically speaking, and how much easier they are to make than they used to be. It’s true that the very best pictures still require large observatories on the ground or in space, but even holding your smartphone to the eyepiece of a consumer-grade telescope can yield images that only a few decades ago would have been the envy of all the world’s astronomers.
And remarkably, this awesome power to casually capture breathtaking celestial snapshots—or selfies, for that matter—with a camera that fits in your pocket traces back, in part, to the work of astronomers using giant telescopes on the ground and in space. Both share a common legacy. Astronomers, it turns out, were among the first to develop and realize the power of digital cameras. Next time you upload a snapshot to social media, don’t forget to thank us. And you’re welcome!
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I’m old enough to have used film cameras when I was young. In high school, I bought a fancy camera and snapped roll after roll of astrophotography through my telescope. It was difficult, expensive and time-consuming but a lot of fun—despite my mom’s complaints about the noxious smells of photographic chemicals coming from my makeshift darkroom where I developed the film.
Professional astronomers used similar techniques back then, but instead of flexible plastic film, they preferred glass plates with light-sensitive material sprayed onto one side. These were loaded into complex (and heavy!) metal boxes that were mounted to the back ends of telescopes and exposed to the target. Once the observations were complete, chemicals were applied to develop the plates and create the photo. The big advantage of this was stability—many archives today still house thousands of plates dating back well more than a century. These priceless troves of data from the past can’t be replicated—but they can’t be erased or corrupted with an errant keystroke, either, like so much of today’s digital images.
But the process of analog astrophotography is arduous, and slow. The tiny, light-reactive grains of chemicals that produce the picture are not terribly sensitive, so exposures take many hours. Even then, seeing faint objects is difficult. Getting quantitative science from them is a pain as well because measuring the brightness of an object recorded this way is arduous and not as precise as one could hope. But for a long time this was the best astronomers—or anyone else—could get, so these drawbacks were tolerable.
In the 1960s, however, a revolution was born. Engineers at Bell Labs realized that a specific kind of semiconductor—a material that carries electricity with an efficiency between that of a conductor such as copper and an insulator such as glass—can be used to detect light and, critically, record the value of an object’s brightness. Arrays of these semiconductors could take the place of film and plates to create a light-sensitive detector, which is the heart of every digital camera. And they could be made in much the same way as another then burgeoning technology, the microprocessor chip, so the manufacturing process was already largely in place.
A big advantage of these detectors is that they’re digital. When light hits pixels (a portmanteau of “picture element”) inside one, that light can be recorded as a voltage in the semiconductor array, which can then be read off as a number, pixel by pixel. This is a very big deal. Numbers can be stored easily and transmitted efficiently over great distances. With analog detectors such as film, each photograph you take is a singular physical object; if you wanted to share it with someone across the country, you’d have to send it to them.
Compare this to a digital image—which can be exactly copied as many times as you wish and distributed far and wide via phone lines or even radio waves—and the advantages over analog photography become overwhelming. And if that’s not enough, digital detectors can be made to “see” different kinds of light by changing the composition of their constituent semiconductors, allowing the creation of digital images in infrared, ultraviolet and other regimes of the electromagnetic spectrum.
Even early on, these semiconductor detectors were far more sensitive than chemical ones. An astronomical image that might take hours of careful observation with film could be done in minutes with a digital camera. Astronomers and space scientists took note of this pretty quickly. (So did spies; in 1976 the National Reconnaissance Office launched the Keyhole-11 KENNEN spy satellite, which was the first to use all-digital detectors—and was also a precursor to the Hubble Space Telescope!). The advantages for interplanetary spacecraft were especially obvious, and engineers at the NASA’s Jet Propulsion Laboratory worked on making these devices smaller, cheaper and more sensitive, with great success.
Whether in a rover on Mars, a satellite orbiting Earth or a smartphone in your backpack, all of these devices boil down to converting light into numbers. For example, a pixel that gets twice as much light as another will store it as a value twice as big. The results can also be processed mathematically—they’re just numbers, after all—and that changed the game for astronomy. An image became an array of numbers, a two-dimensional grid that represented the brightness of the sky at each pixel. It’s difficult to overstate the advantages of this.
For example, some stars in the sky change their brightness very subtly over time. This change depends on some fundamental properties of these stars, including their mass and distance, so measuring those brightness variations accurately reveals these characteristics. The changes can be small and very difficult to measure off a photograph, however. With digital technology, it’s far easier. For one thing, the sensitivity of the detectors means a lot more light is recorded, making measurements simpler. The detectors are more accurate, too, because they essentially count photons, so astronomers can get far more detailed measurements of the star’s brightness—or of the background sky’s brightness, for that matter, which can contaminate an image of the star. But because it’s represented as just a series of numbers, that contamination can simply be removed by subtracting it from the star’s brightness, yielding a better measurement of the true stellar emission.
It’s more complicated than this, of course—typically there’s a lot of mathematical and statistical processing you have to do, and it has to be done carefully—but that’s the gist, and it’s just the tip of the iceberg for how digital images can be used and analyzed in ways not possible for traditional photographs.
Perhaps the most astonishing part of all this is that despite how far this technology has already advanced, it’s still constantly being improved. At first these detectors were small, covering a tiny portion of the sky. Now huge mosaics of detectors can be attached to immense telescopes to gulp down large swaths of the sky every night, with astronomers mining those data to look for asteroids, exploding stars, stars being ripped apart by black holes and even the presence of what might be a hidden planet in our solar system.
The applications beyond just pretty pictures are enormous and have profound impact: Measuring small changes in starlight in galaxies led to a better understanding of dark matter. Seeing supernovas explode billions of light-years away led to the discovery of dark energy. The sensitive digital detectors fed starlight from the giant mirror of the James Webb Space Telescope are helping us see objects at the edge of observable space, changing how we think the first galaxies formed.
And all of this has a direct connection to the smartphone you carry with you. Many come with optics and software that allow you to take impressive photographs of the sky relatively easily. I’ve taken many myself recently, and while they may not be the equal of what we see from NASA’s multibillion-dollar observatories, they’re mine. I took them. If you can, give it a try for yourself! You’re carrying an astronomical revolution in your pocket, and it can deliver the stars to you in a way that would have made young me massively jealous.