Much of the universe is populated by dust that does not glow. It obstructs the view of astronomers. The common elements of hydrogen and helium in the regions between stars absorb starlight and re-emit that energy as glowing gas. They form the filaments and veils of nebulae so common in space. Dust, however, blocks the starlight and creates dark lanes in silhouette against the background of starlight. This galaxy below is a good example. We are seeing it from an edge viewpoint. Click to embiggen.
This is a greatly enlarged view of a galaxy very similar to our Milky Way, but seen edge-on. It was discovered by William Herschel on 6 October 1784. The large amounts of dust in the filaments effectively blocks the visible starlight from the galaxy’s core in the background. The dust makes it very difficult for astronomers to view the structures on the other side.
Sometimes the dust lanes are quite visible even when the view is not edge-on. Here we see a galaxy from directly above. Scottish astronomer James Dunlop discovered this galaxy in 1826. It is about 56 million light years away. The Hubble telescope has very good vision.