Reading a Hubble Image: Dust Lanes and Diffraction Spikes

A NASA Hubble Space Telescope image features NGC 1827, an intermediate spiral galaxy seen edge-on — an angle that makes it a decent primer on what you are actually looking at in a picture of a galaxy.

The first thing to notice is the dust. Rusty-brown dust lanes bisect NGC 1827 lengthwise, so the dust reads as a band laid across the galaxy's light rather than as a detail buried inside it.

The second is depth. Distant galaxies dot the black background, and the foreground stars in the frame are the ones carrying diffraction spikes — the starburst signature that makes a nearby star easy to sort out from the galaxies behind it. Once you know to look for the spikes, the image separates into layers: this galaxy, the stars in front of it, and everything else further back.