When is the last time you watched the sky revolve around us?
Earth rotates on its axis at 1,000 miles per hour (1600 kilometers per hour). At the same time, it flies around the sun at 67,000 m/h (110,000 km/h). And the Sun, with all its planets and rocks and dust in tow, makes its way around the center of the Galaxy, our Milky Way, at 520,000 m/h (830,000 km/h). And then, the Milky Way itself is hurtling toward the nearby Andromeda galaxy at 250,000 m/h (400,000 km/h).
The fastest space craft (and fastest man-made object in history), Juno, will slingshot around Earth on its way to Jupiter, eventually reaching a speed of 165,000 m/h. The NASA space shuttle reaches speeds of 17,000 m/h (27,000 km/h).
The average human walking speed is 3.1 m/h (5.0 km/h).
Though we sit in this coordinated maelstrom, we can still understand all of space and time on the largest scales. But, to do so, we must consider it statistically, on the whole, at great breadth and as a collection – not merely the sum of disconnected parts or separate events.
All across the universe, there are supernovae – exploding stars that blink in a cataclysmic, cosmically infinitesimal moment. Quasars are small regions that surround the supermassive black holes at the centers of galaxies that flash on and off on the timescales of hours to months. Each galaxy in the universe is creating some dimple in space-time due to its mass. Imagine a vast expanse of sand dunes: all light passing by these galaxies must traverse through it, resulting in distorted images by the time they get to us.
These are just some of the events that go on constantly around us, without regard for our existence, as we spin round and round, imagining a static quilt of stars turning about us. And they are just some of the celestial targets that will tell us more about how fast the universe is expanding.
To better understand these events, and the acceleration of spacetime, we wait for the targets to be at a place in the sky when we can see them – when the sun is down and this part of Earth is pointed in their direction. Our targets come from a large swath of sky, one-eighth of the celestial sphere. And across this expanse, we will obtain a uniform sample of targets. The uniformity – homogeneity or constancy – is crucial: we must observe all galaxies brighter than a certain amount, and within a certain distance to have a clean, uniform sample. Otherwise, variations in that information could be misconstrued, or at best they could muddy our measurement of dark energy.
Building the collection starts with amassing a set of deep images of the sky: these are but snapshots of long-gone eons, and they are the first step in our process of discovery. From the images, we distill vast catalogs of celestial bodies – galaxies, stars, motes and seas of hot gas and dust – an accounting of what the universe has so far created. This catalog can be further distilled when studied as a whole. The final concentrate is a small set of numbers that summarizes the fate of our universe: a measurement of the strength of dark energy.
Our spaceship Earth is a pebble in the swirling cosmic sea around us. We watch it as if we are separate, sometimes forgetting we come from it. As we look up from within our snowglobe on a mountaintop in the Chilean Andes, it becomes easier to remember that we are a conduit between the finite and the infinite.
Good night, and keep looking up.
Det. B. Nord
As the Galaxy sets behind the Blanco telescope, our home away from home, we are reminded of where we really are. Earth resides in a mere village of planets, one of many in a city of stars – our Milky Way galaxy – which, as these detectives see it, is our true home.
But it is the distant stars and galaxies, just like those we call home, that betray patterns in our cosmos.
We operate in the dark of night to find as many as we can, as carefully as we can. We track locations, movements, interactions, explosions and lifetimes of millions of individuals. Only these clues in aggregate (for the most part), will lead us down a starlit path to an understanding of our universe’s greatest tug of war: that which is between the pull of gravity and the accelerating expansion of dark energy.
The detectives have gone back to work for Season 2 of observing and combing the logs of photons as they stream into the trap we’ve set, the Dark Energy Camera (DECam). In the coming months, we’re turning these streams into nuggets of knowledge, the first puzzle pieces to be revealed by the Dark Energy Survey (@theDESurvey).
And ultimately this knowledge brings us back home, to understanding our place in the cosmos.
I’m here now at the Blanco, writing this as we prepare for our third night of observations and tracking in Season 2 of DES, with bags under our eyes, coffee mugs in hand, watching the fires in the sky.
Det. B. Nord (@briandnord)
If you run into us where the electrons roam (FB, Twitter, Reddit, etc.), don’t be afraid of the dark – get in touch. We’ll report every two weeks (and occasionally more), and we’ll have more detectives and more ways to tell the stories.
The first season of the Dark Energy Survey is now drawing to a close. For another few weeks, we will continue to watch the sky from the summery Southern Hemisphere. After that, others in the astronomy community will take the reins of the Dark Energy Camera (DECam) until September.
Early in the season, the clouds (and occasionally rain) interrupted this work. For example, in October of 2013, late-evening skies of plum-golden hue gave us the sunsets you see in today’s picture. Even though there were cloudy nights early in the season, this was anticipated. We’re using basic climate and weather models to plan our survey, so we can still observe fruitfully when visibility isn’t the best. Moreover, we can use the data from this past year to improve our survey strategy for the coming four years.
However, the rest of the season has been great, with many nights of very little air turbulence in the atmosphere, meaning we captured very clear images. Astronomers talk about this using the term, “seeing,” which is measured in “arcseconds.” The lower the seeing, the clearer and crisper the images. At the Cerro Tololo Inter-american Observatory, typical values are near one arc-second.
Right now, our squads are sifting through and preparing these images for science, and preparing them to share with you.
In less than a month, the sun will rise on our first season, but the long nights of work will continue.
Det. B. Nord