Noun
blue hour (plural blue hours)
English Wikipedia has an article on:blue hourWikipedia
The period of twilight when the Sun is approximately 4-8° below the horizon and the sky is within a range of blue colors.
Coordinate term: golden hour
It was growing dusk, the blue hour when solid things take on a certain transparency and phantoms become palpable. Kage Baker
Tomorrow X Together’s new EP minisode1 : Blue Hour comes out on Oct. 26. Leading up to the EP, released a special preview for MOAs on Big Hit Entertainment’s social media channels and YouTube. Source: Internet