Photography of the Unseen, Part 2: Astrophotography

The second installment in our two-part series on extreme-scale photography, we take a look at the art, science, and technology of space imaging.

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.

Last month, we took a look at the photography of the microscopic world. This week, we turn our heads upward, and examine the science, art, and technology of astrophotography.

The Technology

Hubble Telescope
The Hubble Telescope

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 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.

Telescope technology has allowed us to peer further into space.

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.

Kepler sensor
Kepler's 42-CCD Sensor

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.

Kepler is equipped with a 95 megapixel camera.

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 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 of 2020. With its 7-mirror, 80-foot wide light-collecting element, the GMT will have 5-10 times the light-gathering power of existing telescopes, including the Hubble.

The Science

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 the observer, and the blue end when moving toward the observer—much like the Doppler effect. This is 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. That famous “Deep Field” image was captured with a 10-day exposure.

What makes it significant is not the perfect exposure of a tiny slice of space, but the objects therein. The 2,000 or so galaxies in the image are calculated to be roughly 12 billion light-years away from Earth, meaning that it's a photo of the universe as it looked 12 billion years ago.

The image itself is of the universe some 12 billion years ago.

A different 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.

Hubble Extreme Deep Field
The Hubble Extreme Deep Field image (2012)

Space photography is also used in the hunt for planets around distant star systems. To date, the Kepler spacecraft has confirmed the existence of 114 exoplanets in 69 different star systems. Earlier this year, astronomers at the Harvard-Smithsonian Center for Astrophysics estimated "at least 17 billion" Earth-sized exoplanets exist in the Milky Way Galaxy, based on data from Kepler.

Kepler has confirmed 114 exoplanets in 69 different star systems.

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).

The Art

Butterfly Nebula
The "Butterfly" Nebula, as seen by Hubble.

Depending on your fascination with space photography, you’ll be either fascinated or disappointed to hear that most of the beautiful, multi-colored images you see of deep space are manipulated to a degree. This is because telescopes like Hubble (and all digital imaging devices for that matter) don’t directly measure the color of incoming light; 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. Some of them include objects that would actually be invisible to the human eye, but are depicted in photographs thanks to color highlighting. NASA explained it best on their official Hubble website: "Creating color images out of the original black-and-white exposures is equal parts art and science.”

Most of the beautiful, multi-colored images you see of deep space are manipulated to a degree.

Clearly, though, the interest in capturing breathtaking images of space is not just a matter of scientific inquiry. Amateur astrophotography has a passionate following among 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, one-minute exposures, lest photos be subject to trailing effects—which can be nice, sometimes.

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—it has an intense 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. Canon even makes a camera specifically for hobbyist astrophotographers: the 60Da.

Carina Nebula
The Carina Nebula "Mystic Mountain."

Astrophotography is more like photomicroscopy than you’d think. They both operate on a deep, humanist fascination with worlds invisible to the naked eye. That fascination is so intense that governments allocate significant portions of their budgets to expanding our knowledge of these worlds.

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 words of the late Carl Sagan...

[All Photos: NASA, Wikipedia Commons]

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