it is a star of a crab that reprsents cancer

The constellation of cancer has been around for around 5 millions years. Cancer is a zodiac constellation and is represented by the crayfish or crab.

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If you mean the constellation cancer, there is no such thing as a "distance to a constellation". It just doesn't make sense. A constellation is basically a general direction in space.

Aside from Cancer being the dimmest zodiacal constellation, the planet Mars is in Cancer (as of 4/21/10)