Like surveyors charting out a parcel of land by measuring angles, distances and elevations, astronomers have long mapped the positions of celestial objects in the sky.
Those celestial maps are about to see some major revisions. New and upcoming campaigns using ground-based telescopes or spacecraft promise to fill in many new details. Together these projects will catalogue positional information on several billion stars and galaxies, near and far.
By scanning the skies for six years, a next-generation space telescope called Euclid ought to map up to two billion galaxies in three dimensions. The mission, which the European Space Agency (ESA) approved this past June for a 2020 launch, will scan about one third of the sky to measure the positions and distances of galaxies across the universe. The hope is that the distribution of cosmic structure will reveal some hidden clue to the nature of dark energy, the unknown entity driving the accelerating expansion of the universe.
A dramatic upgrade to local celestial cartography should come even sooner from ESA's Gaia spacecraft, which is scheduled to launch next year. After arriving in deep space, well beyond the orbit of the moon, Gaia will map the positions and distances of roughly one billion stars. “The main science goal is to address the issues of our Milky Way—the structure and the dynamics,” says Timo Prusti, project scientist for Gaia at ESA.
Meanwhile, back on Earth, many new surveys are now coming online in the Southern Hemisphere, where celestial cartographers can expect to make the greatest impact. In the North, the granddaddy of all astronomical surveys—the Sloan Digital Sky Survey in New Mexico—has already carefully mapped more than one million galaxies in three dimensions, in addition to many other accomplishments.
The telescope most likely to rewrite the books on the southern sky is the Large Synoptic Survey Telescope, or LSST, in Chile. When it comes online around 2022, the LSST—as currently envisioned—will feature an 8.4-meter primary mirror (compared with the Sloan survey's 2.5-meter telescope) and a 3.2-gigapixel digital camera. The mammoth telescope will image the heavens every week to capture transient phenomena such as supernovae and close passages of potentially dangerous asteroids. In the process, it will also mark the three-dimensional location of some four billion galaxies.