In his description of Tartarus , Hesiod says further that Hemera `` day '' , who is now Night 's sister rather than daughter , left Tartarus just as Nyx entered it ; when Hemera returned , Nyx left . In his description of Tartarus , Hesiod says further that Hemera ( day ) , who is Nyx 's daughter , left Tartarus just as Nyx entered it ; when Hemera returned , Nyx left .