Field guide · Deep sky
NebulaDark nebula
A cloud of dust so thick it blots out the stars behind it. You see it as a hole in the Milky Way.
- Made of
- Cold, dense dust and molecular gas
- Seen as
- A starless patch against the Milky Way
- Inside
- Stars not yet born
Some clouds have no star to light them at all. They are only visible because something bright lies behind them — the starry band of the Milky Way — and they block it out like a silhouette.
The Coalsack beside the Southern Cross is the most obvious: a black notch in the Milky Way that sailors noticed centuries before telescopes. The Great Rift, splitting the Milky Way through Cygnus and Aquila, is a chain of them. Inside, where it is cold and shielded, gas is slowly collapsing into the next generation of stars.
Several cultures made constellations out of these shapes rather than out of stars. The Inca saw a llama, a fox and a toad in the dark lanes; Aboriginal Australians see the Emu in the Sky, its head in the Coalsack.
See it in the sky
Each one opens the sky map pointed at it, for tonight, from where you are.