IPA: /ˈluː.mɪ.nəs.li/
KK: /ˈlumɪnəsli/
In a way that produces or reflects light; brightly or glowingly.
The stars shone luminously in the night sky.
Luminously → It is formed from "lumin" (from Latin "lumen", meaning light) and "-ously" (meaning full of or characterized by). The word "luminously" means characterized by or full of light.
Think of 'light' ('lumen') and remember that 'luminously' describes something that is full of light.