The sun sets over rocks in the White Desert north of the Farafra Oasis, southwest of Cairo, Egypt May 15, 2015. Reuters/Amr Abdallah Dalsh

Gordon Shepherd and his colleague Young-Min Cho, atmospheric scientists at York University, have discovered via a study that waves above planet Earth could have caused a “Nocturnal Sun.” Scientists and onlookers have long been perplexed by nights that were almost like days.

Such observations date back to ancient Rome when people could spot details of landscapes far away, identify pebbles on the ground and read documents even if it was night. In the study published in Geophysical Research Letters, the two scientists explain how waves in the Earth’s atmosphere could have made ancient bright nights possible. The waves, also known as zonal waves, were influenced by severe weather on the planet's surface. These travelled around the upper atmosphere.

The bright nights started with a dull light called airglow, found more than 60 miles above the Earth’s surface. The scientists considered four types of zonal waves, the images of which were captured from satellite installed in the 90s to measure the airglow and various features of the atmosphere. The waves peaked at various locations while travelling around Earth. Sometimes they ended up in the same spot. It was somewhat similar to waves in sea piling up together, causing a bigger wave.

The moment these zonal waves superimposed, intensity of the airglow increased to such an extent that even the naked eye could spot it. This explains the nocturnal suns in the past. As the waves moved slowly, they remained superimposed for quite a while. Dr. Shepherd said that the phenomenon typically lasted for two to four nights, and one bright night could cover the entire Europe. In modern times, it is impossible to make out a bright night with so many artificial lights polluting the world.

“We have animal species that are disappearing. We have glaciers that are disappearing. And bright nights too are disappearing, because there are so many city lights everywhere. There are going to be fewer and fewer places where people can see them, and if they did, they’d have to wait a long time,” Dr. Shepherd told The New York Times.

Weather patterns that produce these kinds of waves favour middle latitudes. Our planet’s atmosphere is made up of nitrogen and oxygen in molecular forms. In heights such as 60 miles above Earth’s surface, the sun’s ultraviolet light separates atoms in nitrogen and oxygen molecules clinging together. However, once the sun sets, they come back to reunite, thus releasing energy. This energy is visible as light. It is not visible to the naked eye until an occurence like a bright night happens.

A mysterious alignment of waves in the upper atmosphere amplifies the invisible airglow. Stay tuned on IBT AU for more updates on bright nights and nocturnal suns. [In Case You Missed: Mysteries of Uranus: Scientists fascinated by planet’s magnetosphere; NASA may visit Ice Giant]