The Cosmos: A Digital Frontier
Ever since we started looking up, we tried to picture where the lights in the night were coming from as they moved through the universe. What were these objects – fiery stones, gods?
We kept dreaming about and measuring a world that was hard and too dark to see. And then one day, we could see into its depths.
At first, we only looked out with our eyes, and then we captured light on photographic plates of glass, and then we learned to convert the photons of light into electrical signals that we can store and analyze in computers.
When you sit down at the console, the eight-panel control module first looks like a gamer’s dream. And then you look to your left and you see another multi-panel module. These two consoles alone control the hundreds-ton telescope and $50M Dark Energy Camera (DECam) that captures the light from distant galaxies and exploding stars. These two consoles initiate the process of turning the ancient light into the recorded history of the cosmos. But if you want to know what goes on inside the machines, how we cyber crunch the sky, you have to look behind the scenes at the Data Management system that turns photons into bytes.
The Dark Energy Survey (DES) acquires hundreds of images – nearly a Terabyte of data – every night, and will continue to do so for the next five years. After the light is collected and stored, it must be transferred and cleaned before we can mine it for the faint clues of dark energy. As the images are taken, they are transferred via a high-speed pipeline from the mountaintop of Cerro Tololo in Chile to the corn fields of Illinois, where computer clusters at the National Center for Supercomputing Applications (NCSA; image, upper left) perform calibrations and tests to ensure data are free of error and contamination, to prepare them for cosmological analyses.
While we can observe and measure the sky to great depths, a key partner in this endeavor is our theoretical understanding of cosmic evolution. For this, we must create fake universes, with a variety of different parameters, inside these super-computers. DES will simulate several universes, in which we will test the hundreds of thousands, millions of lines of code in preparation for working with actual data. What’s more, we can compare the simulated universe to our own, telling us which aspects we’ve simulated correctly and which parts of our theories are solid, which need revision. Super-computers, like those at NCSA shown in today’s image (top right and bottom), play a critical role in constructing these universes.
It’s amazing how productive watching the sky can be. But, to look out, we had to bring the universe in.
(Hat tip to Tron: Legacy.)
By: B. Nord [FNAL]
Image: NCSA
Hotel Tololo
The dormitory rooms at the Cerro Tololo Inter-American Observatory (CTIO) in Chile cast a stout shadow over the desert fauna in the light of the early risen moon last February. This night’s moon is so bright, it prevents the Dark Energy Camera from looking at that part of the sky. On bright nights like these, we aim the telescope elsewhere, but still looking, still searching for supernovae and distant galaxies.
We start the night’s work early with an inter-continental tele-conference before dinner. After dinner, we prepare the software and telescope until sunset, when the hunt begins. Working through the night (and through a few pots of coffee and bags of cookies), we emerge a few hundred images closer to understanding dark energy and its effects on the celestial objects deep in the night sky. Just after sunrise, we hit the hay, but our minds often keep crunching numbers or sifting puzzles that arose during our observations, as the work from our night bleeds into our dreamscape.
Welcome to Hotel Tololo. We’ll turn the light off for you.
Written by: Det. B. Nord [FNAL]
Image by: Det. B. Nord
Roadway to the Heavens: the Signal and the Noise
The Sun has long since set, but the Moon keeps its memory alive. In the moonlight, we traverse this short path up to the top of the mountain each night from one of the small houses where we stay for this 10-night astronomical observing stint. Tonight’s drive offers a clear reminder that the path to new knowledge is as winding and uncertain as the roadway to the heavens.
Most nights, clear and dark skies prevail, and the Dark Energy Camera (DECam) has a clean view to the objects in the sky it aims to see. The signals from stars and galaxies arrive unfettered, uninterrupted. Occasionally, however, clouds block light from the celestial sphere, the Moon outshines it and a turbulent atmosphere redirects it. What’s more, the atmosphere itself is constantly at work, emitting light from across the electromagnetic spectrum.
The atmosphere and Moon represent very important sources of noise when observing, especially when incredibly distant and faint objects are the intended targets: DECam is designed to see light from galaxies that are more than 15 billion light-years away. The goal is to get as much signal as possible, while minimizing the effects of all the noise sources, like those mentioned above.
Clouds, like those seen in this week’s image (20-second integration time), block light from stars and galaxies. Less light means less signal. On some nights, the Moon is too bright for the sensitive detectors in DECam, and we have to point the Blanco Telescope away from the moon. Some of the light from the Moon still bounces around the layers of the atmosphere and trickles into the Blanco field of view. Too much scattered light from the Moon or other sources adds to the noise and obscures the signal. Turbulence in the atmosphere deflects light from the objects we seek: multiple layers of air with different temperatures, moving at different speeds heavily disrupt light paths. Consider how the light of a straw is refracted when it goes into a glass of water. This happens in our atmosphere many many times over.
Over the years, astronomers, engineers and climate scientists have worked more and more closely to understand how weather and climate impact astronomical observations. While we’ve come quite far, and we will be able to do exquisite dark energy science at the Blanco, we know there is more road to pave.
Written by: Det. B. Nord [FNAL]
Image Credit: Det. B. Nord [FNAL]
Fire in the Sky
As day gives way to night, our star plummets into the pacific. We refuel our brains for a night of work and then watch the sun scorch the horizon into darkness. This is our nightly ritual.
After dinner, our crew heads back to the telescope. Some of us take a car up the roads, while others make their way up the winding paths through the clay and dirt. Like clockwork, we pass a family of zorros (“foxes”), who often wait outside the kitchen for tasty scraps. There are more mouths to feed now: this past spring, a new litter of pups appeared. Occasionally, a few viscachas (rabbit-like rodents in the chinchilla family) graze on the rare sprig of fauna in the dry mountaintops and then rest on warm rocks in the fading sunlight.
The Dark Energy Survey (DES) observes during these summer months, and the community has priority access to the instrument during the remainder of the year. DES runs optimally during the dry summer (in the southern hemisphere, lasting from December to February) to avoid atmospheric water absorbing and scattering light from the higher-wavelength portions of the electromagnetic spectrum. We desperately need that light to see older, more distant cosmic structures.
On especially dry evenings, a green flash can be seen in the moments before the last of the sun falls below the horizon. Earth’s prismatic atmosphere scatters the suns rays and splits the light by color. As the sun drops, the spread-out spectrum rolls vertically across our eyes, quickly from red to orange and very very briefly through green.
Celestial objects that DES observes set just like the sun does; between the beginning of night and the time a galaxy has fallen below the horizon there is very little time—from minutes to hours. If the Universe were a year old, humanity has existed for about 20 seconds. We have but mere fractions of a moment to take snapshots of these galaxies and stars that have lived for millions and billions of years and that reside millions of light-years away. Utterly ephemeral, the green flash reminds us of the difficulty of our endeavor, of the challenge of catching light from billions of objects so distant in time and space from us.
Dark Skies Turned Gray: Working in the Clouds
We awoke just after two in the afternoon to the eye-itching grogginess that inevitably follows a long night of observing. The afternoon light just barely peeked through the few windows in our dormitory rooms, located more than 60 meters (about 120 feet) below the Blanco Telescope, where we do our nightly work for the Dark Energy Survey (DES).
As we headed to the lunch-flavored breakfast in the cafeteria we spotted a procession of dark clouds to the southeast. To our dismay, the prevailing winds appeared to be carrying them toward us, and toward the Blanco.
During ‘breakfast,’ comprised of tasty fresh vegetables and sausage, we discussed last night’s observations and logistics, as well as plans for the upcoming night, including speculation about the impact of the potentially turbulent weather.
Wet and tumultuous skies scatter the light from distant galaxies and stars that were otherwise on straight paths toward the telescope. This can cause a blurring of images. For telescopes situated on Earth, the higher the mountain-top site, the better the chances of avoiding atmospheric disruptions. The Cerro Tololo Inter-American Observatory resides at about 2200 meters (or 7200 feet) and it enjoys clear, dry skies the vast majority of the time.
Occasionally, mother nature reminds us of her unpredictability and how precious each photon is. With only eight hours of night out of every 24, we need all the darkness we can get. On this afternoon in the early Chilean spring season, our hopes would succumb to the fickle weather. After lunch, we left the cafeteria and looked up to find that a low-flying cloud had come to rest on the mountain peak, enveloping the Blanco. This night, there would be no sky observations, and no photons would break through this wet, gray blanket.
The picture above is taken looking outward from the main door to the control room of the Blanco. The telescope operator, Claudio Aguilera from La Serena, Chile, arrives for the night’s (uneventful) work.
Written by: Det. B. Nord [FNAL]
Image Credit: Det. B. Nord
Moonrise over Tololo
In the east, peeking through a rare mountaintop tree, the Moon rises toward the Milky Way. Not too far behind, the Sun‘s rays reach over nearby mountains to at once expose the valley fog and cover the escape of distant stellar brethren into the daylight.
To the south (on the right) sits the Blanco telescope, readying for its daytime rest. Across the ridge live neighboring telescopes at the Cerro Pachon site, including world-class telescopes SOAR and GEMINI. Can you spot them on the distant ridge? (Hint: in the far right of the photo). The white lines on the ground are metal walkways that astronomers use during the night to move from one building to the other in the utter darkness; their reflectivity allows someone walking to find their way even before their eyes have fully acclimated to the darkness.
It had been a quiet night. Well, they’re all quiet nights: the loudest sound by far originates in the slow whir of motors as domes turn toward new expanses of polka-dot sky. Earlier in the evenings, the temperature drop as day changes into night causes the metal in the domes to contract slightly, and rhythmically—ka-chunk, ka-chunk, ka-chunk. It’s a reminder that we brought these machines to an alien environment, an outpost between humans and the heavens. Nestled within the dome, Blanco and the Dark Energy Camera (DECam) toil away, far more impervious to the elements and designed to be compatible with such temperature changes.
This was one of the last nights of my 10-day run at Cerro Tololo Inter-American Observatory. The moon rose earlier on nights past; when that happens, that part of the sky becomes too bright for the highly sensitive DECam. Nevertheless, we observed several patches of sky to extraordinary depth in the hopes of finding old, distant exploding stars—one of the types of objects that will help illuminate dark energy’s impact on the fate of the cosmos.
Where does moonlight originate? Hints: the moon is not a star, and it is very reflective.
Written by: Det. B. Nord [FNAL]
Image Credit: Det. B. Nord
Dark Energy Detectives 