Dark matter is believed to comprise five-sixths of the matter in the universe, and is one of the strongest pieces of evidence for new fundamental physics. But dark matter does not interact directly with light, making it very difficult to detect except by its gravity. It’s described how various properties of dark matter could lead to observable signals, and how we can attempt to identify those signals from telescope observations. The speaker gives examples of cases where possible signals have been seen, but their origin is not yet fully understood. Furthermore, the speaker discusses how solving the puzzle of those observations will advance our understanding of our Galaxy and cosmos, either by revealing properties of dark matter or providing new insights into astrophysics.