An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

1) Any decapod crustacean of the suborder Brachyura, having the eyes on short stalks and a short, broad, more or less flattened body, the abdomen being small and folded under the thorax. → Cancer; → Crab nebula; → Crab pulsar.
2) Any of various other crustaceans, as the hermit crab, or other animals, as the horseshoe crab, resembling the true crabs (Dictionary.com).

M.E. crabbe; O.E. crabba, from Germanic *krab(b)- (cf. Low Ger. krabben "to scratch, claw"); PIE base *gerbh- "to scratch;" cf. Gk. graphein "to write."

Xarcang "crab," from Mid.Pers. karcang, cf. Lori qerženg from kar-, qer- + cang, ženg "claw." The meaning of the first component, xar/qer, is not clear. It may be related to Av. xruta-, xraoždva- "hard," as in xruždisma- "hard ground" (from xruždi- + zam-), and to the PIE *qarq- "to be hard." In that case, the Pers. term for crab would literally mean "hard claw."

An expanding cloud of debris from the explosion of a → Type I supernova in the → constellation  → Taurus. Its light reached Earth in 1054 and was visible to the naked eye even in the daytime. Lying about 6,300 → light-years away, the Crab nebula is an intense → radio source (Tau A), and also a source of X-rays and gamma-rays. The diameter of the → supernova remnant is about 6 light-years; it is expanding at velocity of 1000 km/sec.

→ crab; → nebula.

A → pulsar discovered in the center of the → Crab nebula in 1969. It is a highly magnetized → neutron star with a radius of 10-15 km that spins 30 times a second.

→ crab; → pulsar.