Hubble is doing double-duty as it peers into the distant universe to observe the Frontier Fields. While one of the telescope’s cameras looks at a massive cluster of galaxies, another camera will simultaneously view an adjacent patch of sky. This second region is called a “parallel field”—a seemingly sparse portion of sky that will provide a deep look into the early universe.
This image illustrates the “footprints” of the Wide Field Camera 3 (WFC3) infrared detector, in red, and the visible-light Advanced Camera for Surveys (ACS), in blue. An instrument’s footprint is the area on the sky it can observe in one pointing. These adjacent observations are taken in tandem. In six months, the cameras will swap places, with each observing the other’s previous location.
Many people are familiar with Hubble’s deep field images, where the telescope stared at what appeared to be relatively empty areas of the sky for long periods of time. Instead of a vast sea of blackness, what astronomers saw in these long exposures were thousands upon thousands of galaxies of all shapes and sizes.
But these deep fields covered just a small fraction of the area of the full moon on the sky. Do they ...