In a sky so full of stars it’s often difficult to figure out where constellations are, one dark spot stands out: The Coalsack Nebula. Parked near one of the five brightest stars comprising the Southern Cross – perhaps the most easily spotted asterism in the southern sky – the nebula looks like an inky black thumbprint.

Where it hangs, the stars struggle to shine. It’s as if someone outlined a portion of the sky and dimmed the lights. What’s really going on with the Coalsack? About 600 light-years away, it’s one of the most prominent dark nebulas, a cloud of water, gases and organic molecules so thick it blots out most starlight. The light that manages to get through is