The Atacama Desert in Chile is one of the driest places on Earth. Clouds are rare, and the air is so devoid of moisture that even the faint light of distant galaxies reaches telescopes without hindrance. But even here, weather follows the Pacific El Niño cycle. It is like an invisible conductor that alternately warms and cools the ocean, and with the water temperature, observing conditions change.

Astronomers from the European Southern Observatory gathered data from four sites at different altitudes. They recorded temperature, humidity, and how strongly the air blurs star images (known as astronomical seeing). These records were then compared with El Niño and La Niña phases. It turned out that during warm El Niño phases the air becomes drier and warmer, while during cold La Niña phases it becomes more humid and cooler. But the blurring itself remains nearly the same.

Now astronomers can align their plans with the Pacific rhythm, just as musicians follow their conductor. And although the conductor is not always predictable, his score is becoming clearer.