We all recognize the infamous atomic blast — the mushroom cloud. But there aren’t any mushroom clouds in space. We know because we tested it.

During the early years of the Cold War, it wasn’t weird to wonder what a nuclear bomb would do if it was detonated in space. Right as the space age began, the idea that the Soviet Union could lob a bomb over the ocean or drop a bomb from an orbiting satellite was a very real fear. To this end, the United States detonated its own nuclear bombs to gather data on what the fallout would look like. Knowing what to expect was the best defense against being caught unprepared.

Many of these atmospheric tests had bombs loaded into B-52 bomber aircraft in Hawaii, bombs that were then dropped and detonated in the skies over the Johnston and Christmas Islands. But some tests took things a little higher. Among the nuclear research and testing programs in the early 1960s was one called Operation Dominic. Within this program were the Fishbowl Events, the highest atmospheric detonations ever done.

These atmospheric tests launched nuclear bombs atop Thor missiles from Johnston Island. The point was to understand how to neutralize an incoming (non-ice giant) threat from a detonation high above the country, and also to understand how nuclear weapon debris would interact with the Earth’s magnetic field in the event of nuclear war. The highest of the Fishbowl events was the Starfish Prime event, where a 1.4 megaton bomb detonated 250 miles above the planet.

These high altitude bombs lit up the night sky the same way a ground-based test did, and the electromagnetic pulses wreaked havoc on electronics. Some of them caused massive blackouts. But instead of the familiar, brilliantly white mushroom clouds, the bombs detonating in the upper atmosphere yielded massive auroras; charged particles interacting with the Earth’s magnetic field spread miles from the detonation site, creating serpentine ribbons of green.

Physical debris from the bomb created filaments in that glowing aurora, and as particles fell back to Earth they burned up in the atmosphere. It was like a deadly light show.

The end of atmospheric testing came in 1963 when President Kennedy signed the Limited Test Ban Treaty in 1963, which put a stop to all atmospheric nuclear testing. But the stamp of those tests lives on. The extra particles that those bombs dispersed have been used as timestamps, allowing us to date everything from trees to fake wine to people.

The detonations may have happened off-world, but their fallout lives on inside your bones.

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