  A ballistic reconstruction of a meteoroid orbit can be made if enough
information is available about its trajectory inside the atmosphere. A few
methods have been devised in the past and used in several cases to trace back
the origin of small impactors. On February 15, 2013, a medium-sized meteoroid
hit the atmosphere in the Chelyabinsk region of Russia, causing damage in
several large cities. The incident, the largest registered since the Tunguska
event, was witnessed by many thousands and recorded by hundreds of amateur and
public video recording systems. The amount and quality of the information
gathered by those systems is sufficient to attempt a reconstruction of the
trajectory of the impactor body in the atmosphere, and from this the orbit of
the body with respect to the Sun. Using amateur and public footage taken in
four different places close to the event, we have determined precisely the
properties of the entrance trajectory and the orbit of the Chelyabinsk event
impactor. We found that the object entered the atmosphere at a velocity ranging
from 16.0 to 17.4 km/s in a grazing trajectory, almost directly from the east,
with an azimuth of velocity vector of 285$^o$, and with an elevation of
15.8$^o$ with respect to the local horizon. The orbit that best fits the
observations has, at a 95% confidence level, a semi-major axis a =
1.26$\pm$0.05 AU, eccentricity e = 0.44$\pm$0.03, argument of perihelion
$\omega$=95.5$^o\pm2^o$ and longitude of ascending node $\Omega$=
326.5$^o\pm0.3^o$. Using these properties the object can be classified as
belonging to the Apollo family of asteroids. The absolute magnitude of the
meteoroid was H= 25.8, well below the threshold for its detection and
identification as a Potential Hazardous Asteroid (PHA). This result would imply
that present efforts intended to detect and characterize PHAs are incomplete.
