Hi Alfredo,

Not entirely sure what you're looking for here. Perhaps
one of the following?

You can hit Alt-U, which causes Guide to center on the
opposition point; then zoom out to cover a large area around
the opposition point, turn asteroids to a desired magnitude,
and see what asteroids are currently near opposition.

Or, you can do much the same thing, and then use Tables...
Current Asteroids, and enter (for example) "16*" to get a
list of all asteroids brighter than mag 16 in that part of
the sky. To do this, you should be using the current "in
testing" version from

http://www.projectpluto.com/new.htm

This ability to get a list of asteroids in a particular
area is described at

http://www.projectpluto.com/new.htm#on_screen_asteroids

Perhaps you are thinking: "I would like to know when
a particular asteroid reaches opposition"? Guide doesn't
have that function (yet). I've been asked about it from
time to time. People would also like to know the time(s)
when a given asteroid will next come close to the earth
or other planet, and its MOID (Minimum Orbital Intersection
Distance, which tells you how close the asteroid _could_
come to the earth, if they were at the right parts of their
orbits at the same time... they might never be there at the
same time, though.)

Or perhaps you are thinking: "I would like a list of
asteroids that will reach opposition in the next week".
This is also something people ask about, but which Guide
doesn't do quite yet.

-- Bill