Nébuleuse Trifide

A red cloud, which emits its own light. A blue halo, which reflects the light of the stars. And bands of dark dust, which cut it into three and give it its name. It is in Sagittarius, nearly 4,000 light-years away according to the Gaia measurement. The red part comes out quickly with the dual-band filter, but that filter does nothing for the blue halo. Here, exposure time without a narrowband filter changes everything.

Sources: Wikipédia en français, Nébuleuse Trifide, NASA, catalogue Messier de Hubble, Messier 20. A figure wrong? Report it.