In 1896, newspapers throughout the United States began reporting accounts of mysterious airships flying overhead. Descriptions varied, but witnesses frequently invoked the century’s great technological achievements. Some sources reported dirigibles powered by steam engines. Others saw motorized, winged crafts with screw propellers. Many recalled a flying machine equipped with a powerful searchlight.

As technologies of flight evolve, so do the descriptions of unidentified flying objects. The pattern has held in the 21st century as sightings of drone-like objects are reported, drawing concern from military and intelligence officials about possible security threats.

While puzzling over the appearance of curious things overhead may be a constant, how we have done so has changed over time, as the people doing the puzzling change. In every instance of reporting UFOs, observers have called on their personal experiences and prevailing knowledge of world events to make sense of these nebulous apparitions. In other words, affairs here on earth have consistently colored our perceptions of what is going on over our heads.

Reports of weird, wondrous, and worrying objects in the skies date to ancient times. Well into the 17th century, marvels such as comets and meteors were viewed through the prism of religion—as portents from the gods and, as such, interpreted as holy communications.

By the 19th century, however, “celestial wonders” had lost most of their miraculous aura. Instead, the age of industrialization transferred its awe onto products of human ingenuity. The steamboat, the locomotive, photography, telegraphy, and the ocean liner were all hailed as “modern wonders” by news outlets and advertisers. All instilled a widespread sense of progress—and opened the door to speculation about whether objects in the sky signaled more changes.

Yet nothing fueled the imagination more than the possibility of human flight. In the giddy atmosphere of the 19th century, the prospect of someone soon achieving it inspired newspapers to report on tinkerers and entrepreneurs boasting of their supposed successes.

The wave of mysterious airship sightings that began in 1896 did not trigger widespread fear. The accepted explanation for these aircraft was terrestrial and quaint: Some ingenious eccentric had built a device and was testing its capabilities.

But during the first two decades of the 20th century, things changed. As European powers expanded their militaries and nationalist movements sparked unrest, the likelihood of war prompted anxiety about invasion. The world saw Germany—home of the newly developed Zeppelin—as the likeliest aggressor. Military strategists, politicians, and newspapers in Great Britain warned of imminent attack by Zeppelins.

The result was a series of phantom Zeppelin sightings by panicked citizens throughout the United Kingdom, Australia, and New Zealand in 1909, then again in 1912 and 1913. When war broke out in August 1914, it sparked a new, more intense wave of sightings. Wartime reports also came in from Canada, South Africa, and the United States. In England, rumors that German spies had established secret Zeppelin hangars on British soil led vigilantes to scour the countryside.

In the age of aviation, war and fear of war have consistently fueled reports of unidentified flying objects. A year after Nazi Germany’s surrender, Sweden was beset by at least a thousand accounts of peculiar, fast-moving objects in the sky. Starting in May 1946, residents described seeing missile- or rocket-like objects in flight, which were dubbed “ghost rockets” because of their fleeting nature. Rockets peppering Swedish skies was well within the realm of possibility—in 1943 and 1944, a number of V-1 and V-2 rockets launched from Germany had inadvertently crashed in the country.

At first, intelligence officials in Scandinavia, Britain, and the United States took the threat of ghost rockets seriously, suspecting that the Soviets might be experimenting with German rockets they had captured. By the autumn of 1946, however, they had concluded it was a case of postwar mass hysteria.