Thanks to decades of conservation efforts, the Hudson River in New York City is the cleanest it’s been since the Civil War and is now home to dolphins.

New York's three closest airports move 140 million people in and out of the most visited place in the United States. But these three travel hubs were not designed to handle this growing number of visitors. Here’s how New York's airports are evolving to handle one of the most complex airspaces on Earth.

Four evenings a year, the brick, steel, and asphalt of Manhattan's cityscape take part in a unique alignment of metropolis and cosmos. The rays of the setting sun align perfectly with Manhattan's street grid—framed by skyscrapers and creating a breathtaking wash of illumination along the cross streets. Frederick P. Rose Hayden Planetarium Director Neil deGrasse Tyson first noted the phenomenon more than a decade ago and coined the term "Manhattanhenge."