Create one finished standalone photographic website background image, 1:1 square, approximately 1536 by 1536 pixels. Theme: Astral atlas. Scene: A small icy comet trails a long, hair-fine turquoise vapor tail diagonally through an otherwise near-empty black field. Art direction: Cinematic astronomical concept art with physically convincing star light, delicate dust and extraordinary scale. Deep black, icy silver, amber and restrained red. Avoid purple, rainbow nebula wallpaper and oversized glitter. Composition: retain generous low-detail top space suitable for overlaying website copy, adapting subject placement naturally. This is the actual background artwork, not a website mockup. No text, letters, typography, logos, borders, collages, grids or watermarks. Full-bleed, polished, richly detailed at native resolution.