Imagine their amazement.

Fortunately, the men who observed this strange object nearly a millennium ago carefully noted its position in the sky: about two breadths of a full Moon northwest of the tip of the star we know as Zeta Tauri, marking the southern horn of Taurus, the Bull. Today when we look to the described location with optical aids, we see a fuzzy patch of stardust with tentacles of incandescent gas moving rapidly outward in all directions, from where a star had literally blown itself apart.

While some stellar explosions are not very great, this one was absolutely devastating, changing the entire character of the star. Modern astronomers call them supernova, from the Latin stella nova or "new star."

But far from being a new celestial object, this burning ball of gas had reached the end of its career and would have better been referred to as a dying star.

A typical nova can maintain a tremendous expenditure of energy for a while, after which it dims back to its former obscurity. At the peak of its eruption, the star blows off its outer layers, increasing its brightness by some 50,000 times or more. Astronomers have even seen cases of stars that have undergone such contortions more than once.

But there is no second time for a supernova.

In the case of the Guest Star of 1054, a star at least ten times more massive than our Sun apparently converted the greater part of its mass instantly into radiant energy; the bursting star suddenly flared to a brilliance equal to perhaps 400 billion suns!

We now know that the stupendous explosion occurred about 6,300 light-years away. So in reality, it actually took place around the year 5246 B.C. But it then took some 6,300 years for the light from that event to reach Earth, in the year 1054.

In the aftermath, little remained. The intensely hot, newly revealed core of the star and an expanding cloud of gaseous debris are today referred to as the Crab Nebula. As of now, the material ejected in the supernova explosion has spread out over approximately 10 light-years of space and, incredibly, its still expanding outward at very high velocity, some 1,100 miles per second (1,800 kilometers per second).

The first person to see the Crab was an English physician and amateur astronomer, John Bevis in 1731. Then on September 12, 1758, Charles Messier recorded what he described as a " . . . nebulosity above the southern horn of Taurus . . . it contains no star; it is a whitish light, elongated like the flame of a taper; discovered while observing the comet of 1758."

The moniker "Crab Nebula" came about from an 1844 sketch of it made by the English astronomer, the third Earl of Rosse.

To see the Crab Nebula for yourself on a fall night, youll have to wait until around midnight local time, after it has risen high enough above the east-northeast horizon. You'll also want a dark, clear sky, for although relatively bright as planetary nebulae go at visual magnitude +8.4, the Crab unfortunately has a tendency to get lost in the background illumination in light polluted locations. It cannot be seen with the naked eye.

The nebula may be just barely visible as a dim patch of light in good binoculars. It is more readily detectable in a 3-inch telescope and begins to appear as irregularly oval-shaped with telescopes of 6-inch aperture or greater.

But to see the delicate outer filamentary structure that gave rise to its name, youll need a much larger telescope, starting at around 16 inches of aperture. Only then -- and only under excellent sky conditions -- will hints of the filaments and fine structure of the nebula begin to become visible.

In November 1968, the core of the exploded star in the Crab Nebula was discovered to be a pulsar; a rapidly rotating neutron star, spinning at an incredible rate of some 30 times per second.

Apparently, there is a "hot spot" on the stars surface, which emits energy in virtually every part of the electromagnetic spectrum. Therefore, as the star whirls on its axis, it appears to "pulse" from our earthly perspective.

This pulsar is but a fraction of the size of our Sun, yet it must be extremely dense in nature, the equivalent of compacting and compressing one solar mass into a volume measuring just 50 miles (30 kilometers) in diameter.

Were it somehow possible to transport just a teaspoon of this material to our Earth, it would likely weigh many hundreds of tons.

In 1987, a naked-eye supernova erupted in the Large Magellanic Cloud, a satellite galaxy of our Milky Way. Unfortunately, at a distance of 190,000 light years, that supernova appeared no brighter to us than a fourth magnitude star.

But during the past thousand years, there have been four recorded supernova in our own galaxy that were truly dazzling to the eye. There is a record of a brilliant supernova that appeared in the year 1006 in the constellation of Lupus, the Wolf. That explosion may have even rivaled the one that would appear in 1054.

Another supernova in 1572 flared out in Cassiopeia, the Queen, and was extensively observed by the Danish astronomer Tycho Brahe. Yet another appeared in the year 1604, this time in the constellation of Ophiuchus, the Serpent Holder. Unfortunately, the appearance of this final supernova occurred just several years before the invention of the telescope.

No other such dazzlers have appeared in our sky since. One has to believe that we are long overdue for another, that some night soon a new star will suddenly appear in the sky.

Perhaps tonight will be that night.