Trade winds are steady, reliable winds that blow from east to west across tropical oceans, roughly between the equator and 30 degrees latitude north and south. These winds got their name because sailing ships used them for centuries to carry trade goods across the ocean. A ship leaving Europe could catch the trade winds blowing west across the Atlantic to reach the Americas, then use different winds farther north to sail back home.

The trade winds form because of how the sun heats Earth. Hot air near the equator rises, and cooler air rushes in from the north and south to replace it. As Earth spins, these winds curve westward. Sailors could count on them: the trade winds blow remarkably consistently, day after day, month after month.

The trade winds follow their own dependable path across the ocean. When Christopher Columbus sailed to the Americas, when Spanish galleons carried silver from Mexico, when merchant ships crossed the Pacific, they all relied on these predictable winds. Before steam engines, knowing where the trade winds blew was essential knowledge for anyone crossing an ocean.