A spyglass is a small, handheld telescope that you hold up to your eye to see distant objects more clearly. Picture a long brass tube that extends and collapses like a mini telescope. Sailors in the Age of Exploration used spyglasses to spot land, identify other ships, or watch for dangerous reefs while still miles away at sea.

The “spy” part of the name comes from using it to observe things from far away without being noticed, though spyglasses weren't just for spies. Ship captains kept them close at hand, and explorers used them to survey new territories. A spyglass might help you see whether that distant ship sailing toward you was a friend or a pirate, or whether those specks on the horizon were birds or an approaching storm.

Unlike modern binoculars that you hold up to both eyes, a spyglass uses just one eye and typically magnifies things 10 to 30 times their normal size. Today they're mostly collector's items or props in pirate movies, since we have better technology. But for centuries, a good spyglass meant the difference between safety and danger, between discovering new lands and sailing blindly into the unknown.