Planetary Picture of the Day - Week of March 16, 2026

Tuesday, 17 March 2026

Ring of Gullion, Northern Ireland

Covered in heath, the solitary rocky hill known as Slieve Gullion rises above the farmland of Northern Ireland in this true-color Landsat image from May 24, 2001. According to Irish mythology, hunter and warrior Finn McCool bathed in the lake on Slieve Gullion and emerged decades older. However, we don’t need a dip in the lake to move through time. A glance at the landscape reveals millions of years of history.

Looking out from the summit of Slieve Gullion, the mythical Finn McCool (or anyone else who climbed to the top, for that matter) would see a ring of rocky hills surrounding the Slieve. From a satellite view hundreds of kilometers above Earth, the formation's circular shape is even more evident. Known as the Ring of Gullion, the ancient hills are nearly 60 million years old. They formed either when an ancient volcano collapsed—leaving a circular fault into which molten rock seeped—or when layers of magma built up in layers in the volcano. This type of formation is called a ring dyke.

Thursday, 19 March 2026

Øresund Strait

This image from the Copernicus Sentinel-1 mission shows us the maritime traffic passing through the Øresund Strait in 2025.

The 118-km-long Øresund Strait (also known as the Sound) separates Denmark to the west from Sweden to the east and links the Baltic Sea to the North Sea, which makes it one of the busiest waterways in the world.

Sentinel-1 satellites carry radar instruments to provide an all-weather, day-and-night supply of imagery of Earth’s surface, making it ideal to monitor ship traffic. Here, more than 50 radar images over the same area, acquired every six days throughout 2025, have been compressed into a single image.

In this image, ships appear as bright, sparkly dots in the dark waters of the strait. The routes of marine traffic are clear to see in the channel, with the main shipping lanes highlighted by the concentration of ships.