The Oxford Names Companion, OUP "Scottish Forenames" - Donald Whyte, FGH, FSG
Notes:
English of unknown origin, possibly from the Latin "heaven", via the French Céline. It is also spelt Selena in the 1841 Census of Aberdeenshire. The latter spelling relates to Cēlēne, the Greek moon goddess.
Thanks to Donald Whyte who provided much of the initial information for this site.