What is the Crab nebula?
The starry constellations were named before the dawn of history, many of them in honor of sacred totem animals. We need imagination to see these animals in Leo the Lion and Taurus the Bull. But the Crab nebula was named in recent times and it does look somewhat like a crab.
This filmy cloud of luminous gas is invisible without a telescope which is a p1ty. For it is one of the most beautiful objects in the heavens. After centuries of detective work, astronomers have traced back its history and found it to be one of the most dramatic of all heavenly spectacles.
The story of the Crab nebula began, so we think, some 6,000 years age, when earthlings were naming the constellations, building Stonehenge and planning the first pyramids. A distant star, too dim to be noticed, suddenly exploded and became a brilliant supernova, Such a dazzling event occurs in our Galaxy perhaps two or three times in a thousand years.
Light from the explosion whisked across space traveling at 186,000 miles a second. Some 5,000 years later, it reached the earth with nem of the dramatic event. Astronomers in China and Japan saw a new star, bright as Jupiter, in, the constallation Taurus the Bull. It soon faded, so they named it the Guest Star and noted its position in their records.
This phase of a supernova is very short and the Guest Star as soon forgotten. Then, in 1764, a strange object was spotted through a telescope located on a Paris rooftop. It was a nebulous clod of gases fringed with filaments like sprawling tenacles.
The Crab nebula seemed a suitable name, but it took almost 200 years of patient figuring to trace its dramatic story.
From end to end, the Crab measures six light years, It is big enough to swamp the Solar System and reach beyond the nearest stars. Its fuzzy gases are still expanding at 600 miles a second and the sprawling tentacles grow 35 million miles longer every day. It; is between 5,000 and 6,000 light years away. With this information, astronomers reasoned that the expanding cloud of gases was started from an exploding supernova which might have been seen from the earth some 900 years ago, In the old records, they found the Guest Star.
It occured at the right time and in the right part of the sky and could well have been the supernova which caused the Crab nebula.
Our news of events in the Crab nebula is more than 5,000 years late, for it takes the light beams which carry the pictures al? this time to reach us. Our pictures of Crab show what was happening in the dim past and by now its hazy gases may have mingled with the dust of the Galaxy.