Essential Grammar plus Supplementary Exercises with Key Pack (количество томов: 2)

Last seen in October 1911, it was finally tracked down in 2000 after being missing for eighty-nine years. So from the point of view of asteroid research the twentieth century was essentially just a long exercise in bookkeeping. It is really only in the last few years that astronomers have begun to count and keep an eye on the rest of the asteroid community. As of July 2001, twenty-six thousand asteroids had been named and identified-half in just the previous two years. With up to a billion to identify, the count obviously has barely begun. In a sense it hardly matters. Identifying an asteroid doesnБЂ™t make it safe. Even if every asteroid in the solar system had a name and known orbit, no one could say what perturbations might send any of them hurtling toward us. We canБЂ™t forecast rock disturbances on our own surface. Put them adrift in space and what they might do is beyond guessing. Any asteroid out there that has our name on it is very likely to have no other. Think of the EarthБЂ™s orbit as a kind of freeway on which we are the only vehicle, but which is crossed regularly by pedestrians who donБЂ™t know enough to look before stepping off the curb ...»