SPACE — Astronomer Carl Sagan first noticed flashes of light on our home planet back in 1993. But the mystery of what they were would not be cracked until 24 years later.

NASA’s Earth Polychromatic Imaging Camera onboard the Deep Space Climate Observatory, or DSCOVR, is about a million miles from Earth, and it has been capturing strange light bursts reflecting off the planet’s surface that appear over both land and water, according to a NASA press release.

Researchers found 866 glints in images taken from the DSCOVR spacecraft between June 2015 and August 2016, and theorized that they were caused by reflected sunlight.

Under the laws of reflection, the bursts had to be limited to certain spots. The angle between the Sun and Earth should be the same as the angle between Earth and the spacecraft, to allow the reflected light to be picked up.

When the locations of the glints were plotted out, they matched the angles.

Researchers further discovered that the source of the reflection appeared to be ice crystals in high-altitude cirrus clouds. Sunlight would bounce off horizontally-oriented particles and create the bright flashes.

With that mystery solved, the researchers are now looking to study the ice crystals, in the hopes of determining whether they have an impact on how much light passes through the atmosphere.