Medium-sized astrapia with long, markedly graduated tail. Male nominate race has brilliantly iridescent metallic yellowish-green crown, nape and mantle, metallic blue-green chin and throat with blue to purple sheen in suitable lights; velvety black back with rich magenta sheen, matt black rump and uppertail-coverts; dark greyish-brown upperwing, slight purplish-blue iridescence at leading edge (above primary coverts); rectrices blackish-brown, inner four pairs with variable extent of white on bases and shafts, central pair having black broad spatulate tips with slight iridescent magenta gloss, tail feathers with tiny hair-like central points at tips; broad, strongly iridescent coppery-red gorget narrowing as it extends up breast side to side of face to beneath eye; remaining underparts silk-like oily dark green, with some larger plate-like feathers at breast side with strong, paler, lime-green iridescence; matt blackish-brown thighs, vent and undertail-coverts; iris dark brown to blackish-brown; bill shiny black; legs fleshy lead-grey. Female is smaller than male, radically different plumage, head, nape and throat brownish-black with bluish-green iridescent gloss, drab blackish-brown on upperparts down to chest, below finely barred dusky brown and buff. Juvenile is like female but plumage soft and fluffy, duller and less black above, less rufous in underparts, more grey on chin, throat and upper breast, and tail feathers more pointed; immature like adult female but dark chestnut-brown on crown, sometimes with variable amount of chestnut-rufous in crown; subadult male varies, like adult female but with few feathers of adult male plumage intruding, to like adult male with few feathers of female plumage remaining, initial part of adult plumage acquired is glossy green feathering on crown and throat; male tail becomes progressively shorter with age. Race helios is larger than nominate, has extensive, unconcealed white bases on underside of outer primaries (except outermost two), adult male more bluish and less golden-green on crown, neck and dorsal collar, broader spatulate tips on central pair of rectrices, female-plumaged birds slightly darker above.