  This article describes a citizen-science project conducted by the Spanish
Virtual Observatory (SVO) to improve the orbits of near-Earth asteroids (NEAs)
using data from astronomical archives. The list of NEAs maintained at the Minor
Planet Center (MPC) is checked daily to identify new objects or changes in the
orbital parameters of already catalogued objects. Using NEODyS we compute the
position and magnitude of these objects at the observing epochs of the 938 046
images comprising the Eigth Data Release of the Sloan Digitised Sky Survey
(SDSS). If the object lies within the image boundaries and the magnitude is
brighter than the limiting magnitude, then the associated image is visually
inspected by the project's collaborators (the citizens) to confirm or discard
the presence of the NEA. If confirmed, accurate coordinates and, sometimes,
magnitudes are submitted to the MPC. Using this methodology, 3,226 registered
users have made during the first fifteen months of the project more than
167,000 measurements which have improved the orbital elements of 551 NEAs (6%
of the total number of this type of asteroids). Even more remarkable is the
fact that these results have been obtained at zero cost to telescope time as
NEAs were serendipitously observed while the survey was being carried out. This
demonstrates the enormous scientific potential hidden in astronomical archives.
  The great reception of the project as well as the results obtained makes it a
valuable and reliable tool for improving the orbital parameters of near-Earth
asteroids.
