sentences:  William Parsons, 3rd Earl of Rosse observed the nebula at Birr Castle in 1844 using a telescope, and referred to the object as the "Crab Nebula" because a drawing he made of it looked like a crab.He observed it again later, in 1848, using a telescope and could not confirm the supposed resemblance, but the name stuck nevertheless.In 1913, when Vesto Slipher registered his spectroscopy study of the sky, the Crab Nebula was again one of the first objects to be studied.