Photography of the Unseen, Part 2: Astrophotography
The second installment in our two-part series on extreme-scale photography.
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This article was originally published on June 13, 2013. It has since been updated with new information. April 1, 2016
Our fascination with objects that are too large or too distant to observe is perhaps just as intense as our fascination with objects that are too small. Nonetheless, these disciplines require entirely different concentrations of science and technology, and they result in completely different modes of expression.
We've already taken a close look at the photography of the microscopic world. Here we turn our heads to the sky to examine the art, science, and technology of astrophotography. And with today's release of a photo of the center of our galaxy taken by the Hubble Space Telescope, it seems more appropriate than ever to take a look at how all those breathtaking images of space are brought down to Earth.
The first thing that comes to mind when you think of space photography is probably the Hubble Telescope. A 24,500-pound orbital telescope, the Hubble was launched in 1990 and has taken some of the most iconic images of space in history. Built by NASA, Hubble features a nearly 8-foot mirror, polished to an accuracy of 10 nanometers—roughly the thickness of a bacterial cell wall. This allows the sensor to capture a wide spectrum of electromagnetic radiation, including ultraviolet light.
Hubble's successor is the James Webb Space Telescope, which is scheduled for launch in late 2018. This device will feature a much larger 6.5-meter diameter, gold-coated beryllium reflector with advanced infrared sensors, allowing it to observe more distant objects across a wider heat spectrum.
The Kepler spacecraft, launched in 2009, roughly follows Earth's orbit around the sun, but is distant enough to measure minute light changes from distant stars, the extent of which can suggest the presence of Earth-like planets orbiting them. To do this, Kepler is equipped with a 95-megapixel camera made up of 42 CCD sensors, each at 2200×1024 pixels. According to NASA, this made it the largest camera ever sent to space at the time of launch.
But astrophotography is not limited to extraterrestrial spacecraft. Up until a few decades ago, all images of space were taken from the ground. In the 19th century, shortly after the invention of the Daguerreotype camera, photographers learned that prolonged exposures of the sky could render images of stars and distant objects otherwise invisible to the naked eye. But it wasn't until the advent of the dry plate that astrophotography took off.
Aided by breakthroughs in astrophysics, observatories and large-scale telescopes began popping up all over the world. New camera designs such as the Schmidt and Lurie–Houghton telescopes offered enormous fields of view—perfect for rendering wide astronomical surveys and cosmic-scale images.
Today, the European Southern Observatory's aptly named "Very Large Telescope" is the Hubble of terrestrial telescopes. Located in Chile, it features four separate 8.2-meter mirrors, allowing it to observe both visible and infrared radiation, and it can capture some truly remarkable images. According to the ESO, the VLT can detect objects that are 4 billion times fainter than what can be seen with the naked eye.
Also in Chile is the Giant Magellan Telescope, which is aiming for a completion date in the early 2020s. With its 7-mirror, 80-foot wide light-collecting element, the GMT will have 5 to 10 times the light-gathering power of existing telescopes, including the Hubble.
Einstein's explanation of the interconnectedness of space and time contributed to our understanding of a phenomenon called "redshift"—in which radiated light shifts toward the red end of the electromagnetic spectrum when emitted from objects moving away from an observer, and to the blue end when moving toward the observer. It's sort of like the Doppler effect for light, and it's critical to understanding the motion and energy of celestial bodies, as well as how to interpret astronomical images.
American astronomer Edwin Hubble, after whom the telescope is named, is credited with the discovery that the universe is actually expanding, and he came to this conclusion thanks to an understanding of redshift.
Fittingly, one of the Hubble telescope's most iconic images, taken many decades after Hubble's death, depicts a young universe in the early stages of expansion. The famous "Deep Field" image was captured with a 10-day exposure.
What makes it significant is not the perfect exposure of a tiny sliver of space, but the objects within it. The 2,000 or so galaxies in the image are calculated to be roughly 12 billion light-years away from Earth. In other words, it's a photo of the universe as it appeared 12 billion years ago.
A separate 23-day exposure, called the "Extreme Hubble Deep Field," was taken in 2012 and depicts light from 13.2 billions years ago. The universe itself is estimated to be 13.7 billion years old, so this image shows a universe that is only 500 million years old.
Space photography is also used in the hunt for planets around distant star systems. To date, the Kepler spacecraft has confirmed the existence of more than 1,000 exoplanets across 440 star systems. In 2013, astronomers used Kepler data to predict the presence of up to 40 billion Earth- or super-Earth-sized planets in the Milky Way galaxy.
In June, the ESO released an image of a "gas giant" planet 300 light years from Earth. Direct imaging of exoplanets is difficult, because astronomers use spectrometry—specifically, light shifts in the spectrum of parent stars—to confirm the presence of extrasolar objects. So the direct image of an exoplanet is rare, but not impossible.
The first image of a distant planet came in 2008, when astronomers at the Gemini telescope in Hawaii snapped an image of a star system with a planet eight times as massive as Jupiter. From the light it emits, scientists were able to determine the age of the star (5 million years) and the temperature of the planet (more than 2,700°F).
You'll probably be either fascinated or disappointed to hear that most of the beautiful, multi-colored images you see of deep space are manipulated to some degree. This is because telescopes like Hubble (and all digital imaging devices, for that matter) don't directly measure the color of incoming light. Instead, they use filters to absorb only specific wavelengths.
Thus, the colors in these images are only approximations of what distant objects like galaxies and nebulae might look like if we were able to see them with the naked eye. Some include objects that would actually be invisible to our vision, but are depicted in photographs thanks to color highlighting. NASA explains it best on its official Hubble website: "Creating color images out of the original black-and-white exposures is equal parts art and science."
Capturing breathtaking images of space isn't just for credentialed scientists. Astrophotography has a passionate following among hobbyist photographers and astronomers alike. However, because it's difficult to coordinate the movement of the Earth with the position of your average backyard telescope, this branch of photography is mostly limited to brief exposures (typically one-minute or less), lest photos be subject to trailing effects. (Those are great for artistic effect, but not so useful when you want clear shots of distant celestial bodies.)
But that doesn't mean these photographers aren't capable of snapping awe-inspiring images of the night sky. Amateur astronomy is anything but a fringe hobby, with an intense worldwide following. Each year in England, the Royal Observatory Greenwich hosts the Astronomy Photographer of the Year competition, showcasing some of the best works in the field. A similar competition hosted by astrophotography group The World at Night focuses on images of both the earth and sky.
Astrophotography is more like photomicroscopy than you may think. They both operate on a deep, humanist fascination with worlds invisible to the naked eye—a fascination so intense that governments allocate significant portions of their budgets to expanding our knowledge of how they work.
You can expect this same motivation to drive large-scale photography in the future, allowing us to peer that much deeper into the atom and that much further into space. Until then, let's enjoy the inspiring words of the late Carl Sagan...