In Norse mythology, Nótt (Old Norse "night") is night personified, grandmother of Thor. In both the Poetic Edda, compiled in the 13th century from earlier traditional sources, and the Prose Edda, written in the 13th century by Snorri Sturluson, Nótt is listed as the daughter of a figure by the name of Nörvi (with variant spellings) and is associated with the horse Hrímfaxi, while the Prose Edda features information about Nótt's ancestry, including her three marriages. Nótt's third marriage was to the god Dellingr and this resulted in their son Dagr, the personified day (although some manuscript variations list Jörð as Dellingr's wife and Dagr's mother instead). As a proper noun, the word nótt appears throughout Old Norse literature.
In the Prose Edda book Gylfaginning, Nótt is again personified. In chapter 10, the enthroned figure of High states that Nótt is the daughter of a jötunn from Jötunheimr by the name of "Norfi or Narfi". Nótt is described as "black and swarthy", and has had three marriages. Her first marriage was with Naglfari, and the two produced a son by the name of Auðr. Nótt's second marriage was to Annar, resulting in their daughter Jörð, the personified earth. Finally, Nótt marries the god Dellingr, and the couple have Dagr, who takes after his "father's people" in brightness and fairness. Odin took Nótt and her son Dagr, placed them into the sky with a chariot and a horse each, and they ride around the earth every 24 hours. Nótt rides before Dagr, and foam from her horse Hrímfaxi's bit sprinkles the earth.
However, scholar Haukur Thorgeirsson points out that the four manuscripts of Gylfaginning vary in their descriptions of the family relations between Nótt, Jörð, Dagr, and Dellingr. In other words, depending on the manuscript, either Jörð or Nátt is the mother of Dagr and partner of Dellingr. Haukur details that "the oldest manuscript, U, offers a version where Jǫrð is the wife of Dellingr and the mother of Dagr while the other manuscripts, R, W and T, cast Nótt in the role of Dellingr's wife and Dagr's mother", and argues that "the version in U came about accidentally when the writer of U or its antecedent shortened a text similar to that in RWT. The results of this accident made their way into the Icelandic poetic tradition".
In the Prose Edda book Skáldskaparmál, means of referring to Jörð are provided, including "daughter of Nótt". Chapter 58 states that "Hrimfaxi or Fiorsvartnir draw the night", and in chapter 64, "nótt" is stated as one of various words for time and a version of the Alvíssmál passage is cited.