Revelation Chapter 6, Verse 13 (NASB)

^6:13 and the stars of the sky fell to the earth, as a fig tree casts its unripe figs when shaken by a great wind.

and the STARS of the sky FELL to the earth,

Stars, from a Revelation perspective, are any space objects other than the sun and moon. They may literally be the stars we see at night (hot gaseous bodies like our sun) or planets or comets or other unheated objects. Since this verse is a continuation of the previous verse, this implies that some of the STARS are massive enough that they are not entirely burned up in the atmosphere before striking the earth.

Our astromoners tell us that there is a band of asteroids near the outer rim of our solar system which may have eccentric enough orbits such that a cluster of asteroids would intercept the earth's orbit. Even though space is almost empty, our moon's surface and its many crater pock marks indicate that collisions between orbiting bodies is not that rare. It appears that this is what this broken seal is describing.

as a fig tree casts its unripe figs when shaken by a great wind.

While the fig tree in scripture has many symbolic meanings, here it is used as the common example of the impact or force with which the STARS will collide with the earth. This is part of the 'shaking' the prophet Haggai refers to, Haggai 2:1-9.

This portion of the verse also indicates that there will be an excessive wind (globally) generated from the impacts. This seems reasonable in light of our experiences with manmade and natural explosions (like Mount St. Helens, for example, where trees were knocked down for miles around the mountain). Hundreds even thousands of miles from the impact site, the 'ping of unripe figs' will be felt. With an impact this large, large chunks of the earth's surface would be dislodged and propelled to such heights that these chunks will fall back to earth miles from the 'zero ground'. Each of these chunks would then cause its own mini crater and dust plume. Hence, worldwide the sun can be made dark and the moon look like blood.

Update: recent studies of other stellar/galaxy systems seem to indicate that this may be a solar micronova^a..