Unearthly a. : Not terrestrial; supernatural; preternatural; hence, weird; appalling; terrific; as, an unearthly sight or sound.

Example:
Why is the phoksundo lake have an Unearthly turquoise blue color?

Taxonomy
Jem, earth, Rae, preternatural, alien, Star, Synonyms, translation, Antonyms, Nikki, Shane, Houghton Mifflin Company, Unnaturally, Thesaurus, Episode, Science Fiction TV, Literature & Language, Unanswered questions.

Defination from the web:
unearthly adj. , -lier , -liest . Not of this earth; preternatural; supernatural. Unnaturally strange and frightening ... Unearthly is an shōjo Original English-language manga series written by Ted Naifeh, with art by Elmer Damaso and is published by Seven Seas Entertainment. ...