River of Dreams
The Dark Energy Survey, in its search for distant cosmic secrets, needs many nights of clear sky. Unfortunately, on this night, a river of clouds flowed overhead. We often look so far away to the faintest objects, that a wisping of cottony clouds moving over the Blanco telescope requires extra attention. In these cases, we might change our observing strategy to look at parts of the sky that require less detail.
As we sift through the tons of sediment and the terabytes of data, occasionally the clouds get so heavy and consuming that we must close the telescope dome to preserve the instrument. In these cases, we still use the time wisely: our Dark Energy Calibrations (DECal) team has developed a method to precisely measure and characterize the flow of light through the telescope at every relevant wavelength, and to monitor for any changes in that flow over the years of the survey.
As we fish for light in the sky, we cast a broad net. In the river of dreams, we sift through sediment for celestial gold.
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
Dark Energy Detectives 