Delphinus, small constellation in the northern sky at about 21 hours right ascension and 10° north in declination. The brightest star in Delphinus is Rotanev, with a magnitude of 3.63. The four brightest stars form a diamond-shaped asterism called “Job’s Coffin.” In Greek mythology there are two stories about this constellation. In one, it is the messenger of the sea god Poseidon. In the other, it is the dolphin that rescued the poet Arion from drowning.