Some events in astronomy are hard to watch if you don't have a really powerful telescope and dark skies. In these cases, a computer can come in handy. That will be true this weekend when Saturn passes in front of a hard-to-see but spectacular patch of light in the sky.

Back on July 4, in the year 1054 AD, a stellar explosion of cataclysmic proportions took place: a supernova. A star, probably at least ten times more massive than our own Sun, suddenly blew apart; the bursting star likely blazing as brilliantly as our entire galaxy, the equivalent of 400 billion normal stars.

In the aftermath, nothing remained, except the intensely hot, newly revealed core of the star and an expanding cloud of gaseous debris.

The "guest star" that suddenly appeared, could easily be seen in daylight for 23 consecutive days. It finally faded completely from view after 653 days. The gas cloud that remained from the explosion is popularly known as the Crab Nebula and the cloud is still expanding outward in all directions at roughly 1,100 miles every second (1,800 kilometers per second).

During the night of January 4-5 this year, skywatchers looking toward that exact spot where the stellar explosion of 1054 took place will instead see a very bright, yellowish-white star-like object, which will be none other than the ringed planet Saturn.

While initially the 1054 supernova blazed more than 250 times brighter, it is not out of the question that perhaps almost a year after its stupendous outburst, the supernova might very well have diminished to a brightness and color similar to that of Saturn right now.

In fact, if you train a telescope toward Saturn on the night of January 4-5, it will appear to be situated in front of the Crab Nebula. It is not very likely however, that the Crab will be visible at all to most telescopic observers, since it only shines at ninth magnitude, while Saturn currently glows at a far more brilliant magnitude of 0.4. That means that Saturn is some 5,800 times brighter than the Crab and likely will overwhelm the nebula with its light.

Currently, Saturn appears to be looping backward or to the west among the background stars. This is known as retrograde motion and is an artifact of the Earth overtaking Saturn as both planets move in their respective orbits around the Sun.

Eventually, this backward motion will be cancelled out and Saturn will appear to come to halt and resume its normal eastward course. This will happen on Feb. 22.

Then, on April 9, Saturn will pass the Crab Nebula again, but this time it will only be a near miss, with Saturn slipping about 19 arc minutes (about two-thirds of the apparent width of the Moon) to the north of the nebula.