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This Week's Sky at a Glance, November 28 – December 7
Saturn remains super-thin-ringed high after dark. The interstellar comet, 11th magnitude, is now nice and high in the dark before dawn. Don't wait; moonlight approaches.
The post This Week's Sky at a Glance, November 28 – December 7 appeared first on Sky & Telescope.
Our verdict on sci-fi novel Every Version of You: We (mostly) loved it
Our verdict on sci-fi novel Every Version of You: We (mostly) loved it
Read an extract from The Player of Games by Iain M. Banks
Read an extract from The Player of Games by Iain M. Banks
Why sci-fi novelist Iain M. Banks was an ‘astounding’ world-builder
Why sci-fi novelist Iain M. Banks was an ‘astounding’ world-builder
Earth from Space: Eye of the Sahara
Supermassive dark matter stars may be lurking in the early universe
Supermassive dark matter stars may be lurking in the early universe
Rings of Rock in the Sahara
In northeastern Africa, within the driest part of the Sahara, dark rocky outcrops rise above pale desert sands. Several of these formations, including Jabal Arakanū, display striking ring-shaped structures.
Jabal Arkanū (also spelled Arkenu) lies in southeastern Libya, near the border with Egypt. Several other massifs are clustered nearby, including Jabal Al Awaynat (or Uweinat), located about 20 kilometers (12 miles) to the southeast. Roughly 90 kilometers to the west are the similarly named Arkenu structures. These circular features were once thought to have formed by meteorite impacts, but later fieldwork suggested they resulted from terrestrial geological processes.
Arkanū’s ring-shaped structures also have an earthly origin. They are thought to have formed as magma rose toward the surface and intruded into the surrounding rock. Repeated intrusion events produced a series of overlapping rings, their centers roughly aligned toward the southwest. The resulting ring complex—composed of igneous basalt and granite—is bordered to the north by a hat-shaped formation made of sandstone, limestone, and quartz layers.
This photograph, taken by an astronaut aboard the International Space Station on September 13, 2025, shows the massif casting long shadows across the desert. The ridges stand nearly 1,400 meters above sea level, or about 800 meters above the surrounding sandy plains. Notice several outwash fans of boulders, gravel, and sand spreading from the mountain’s base toward the bordering longitudinal dunes.
Two wadis, or typically dry riverbeds, wind through the structure. However, water is scarce in this part of the Sahara. Past research using data from NASA and JAXA’s now-completed Tropical Rainfall Measuring Mission (TRMM) indicated that southeastern Libya, along with adjacent regions of Egypt and northern Sudan, receives only about 1 to 5 millimeters of rain per year. Slightly higher accumulations, around 5 to 10 millimeters per year, occur near Jabal Arkanū and neighboring massifs, suggesting a modest orographic effect from the mountains.
Astronaut photograph ISS073-E-698446 was acquired on September 13, 2025, with a Nikon Z9 digital camera using a focal length of 800 millimeters. It is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. The image was taken by a member of the Expedition 73 crew. The image has been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Story by Kathryn Hansen.
References & Resources- Afkareen, M. M., et al. (2022) Lineament Mapping of Jabal Arkenu in Southern Libya. The Scientific Journal of University of Benghazi, 35(1).
- Alghariani, M. (2020) Applications of Remote Sensing for Exploration of Mineral Deposits and Gold in Jabal Arkenu. Fourth International Conference on Geospatial Technologies Libya GeoTec4 in Tripoli – Libya.
- Cigolini, C., et al. (2012) Endogenous and nonimpact origin of the Arkenu circular structures (al-Kufrah basin—SE Libya). Meteoritics & Planetary Science, 47(11), 1772-1788.
- Kelley, O. A. (2014) Where the Least Rainfall Occurs in the Sahara Desert, the TRMM Radar Reveals a Different Pattern of Rainfall Each Season. Journal of Climate, 27(18), 6919–6939.
- NASA Earth Observatory (2024, January 23) Water Beneath the Sand. Accessed October 30, 2025.
- NASA Earth Observatory (2013, March 9) Jebel Uweinat. Accessed October 30, 2025.
- NASA Earth Observatory (2008, November 10) Arkenu Craters, Libya. Accessed October 30, 2025.
JPEG (4.54 MB)
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Earth Science Data
Rings of Rock in the Sahara
In northeastern Africa, within the driest part of the Sahara, dark rocky outcrops rise above pale desert sands. Several of these formations, including Jabal Arakanū, display striking ring-shaped structures.
Jabal Arkanū (also spelled Arkenu) lies in southeastern Libya, near the border with Egypt. Several other massifs are clustered nearby, including Jabal Al Awaynat (or Uweinat), located about 20 kilometers (12 miles) to the southeast. Roughly 90 kilometers to the west are the similarly named Arkenu structures. These circular features were once thought to have formed by meteorite impacts, but later fieldwork suggested they resulted from terrestrial geological processes.
Arkanū’s ring-shaped structures also have an earthly origin. They are thought to have formed as magma rose toward the surface and intruded into the surrounding rock. Repeated intrusion events produced a series of overlapping rings, their centers roughly aligned toward the southwest. The resulting ring complex—composed of igneous basalt and granite—is bordered to the north by a hat-shaped formation made of sandstone, limestone, and quartz layers.
This photograph, taken by an astronaut aboard the International Space Station on September 13, 2025, shows the massif casting long shadows across the desert. The ridges stand nearly 1,400 meters above sea level, or about 800 meters above the surrounding sandy plains. Notice several outwash fans of boulders, gravel, and sand spreading from the mountain’s base toward the bordering longitudinal dunes.
Two wadis, or typically dry riverbeds, wind through the structure. However, water is scarce in this part of the Sahara. Past research using data from NASA and JAXA’s now-completed Tropical Rainfall Measuring Mission (TRMM) indicated that southeastern Libya, along with adjacent regions of Egypt and northern Sudan, receives only about 1 to 5 millimeters of rain per year. Slightly higher accumulations, around 5 to 10 millimeters per year, occur near Jabal Arkanū and neighboring massifs, suggesting a modest orographic effect from the mountains.
Astronaut photograph ISS073-E-698446 was acquired on September 13, 2025, with a Nikon Z9 digital camera using a focal length of 800 millimeters. It is provided by the ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center. The image was taken by a member of the Expedition 73 crew. The image has been cropped and enhanced to improve contrast, and lens artifacts have been removed. The International Space Station Program supports the laboratory as part of the ISS National Lab to help astronauts take pictures of Earth that will be of the greatest value to scientists and the public, and to make those images freely available on the Internet. Additional images taken by astronauts and cosmonauts can be viewed at the NASA/JSC Gateway to Astronaut Photography of Earth. Story by Kathryn Hansen.
References & Resources- Afkareen, M. M., et al. (2022) Lineament Mapping of Jabal Arkenu in Southern Libya. The Scientific Journal of University of Benghazi, 35(1).
- Alghariani, M. (2020) Applications of Remote Sensing for Exploration of Mineral Deposits and Gold in Jabal Arkenu. Fourth International Conference on Geospatial Technologies Libya GeoTec4 in Tripoli – Libya.
- Cigolini, C., et al. (2012) Endogenous and nonimpact origin of the Arkenu circular structures (al-Kufrah basin—SE Libya). Meteoritics & Planetary Science, 47(11), 1772-1788.
- Kelley, O. A. (2014) Where the Least Rainfall Occurs in the Sahara Desert, the TRMM Radar Reveals a Different Pattern of Rainfall Each Season. Journal of Climate, 27(18), 6919–6939.
- NASA Earth Observatory (2024, January 23) Water Beneath the Sand. Accessed October 30, 2025.
- NASA Earth Observatory (2013, March 9) Jebel Uweinat. Accessed October 30, 2025.
- NASA Earth Observatory (2008, November 10) Arkenu Craters, Libya. Accessed October 30, 2025.
JPEG (4.54 MB)
You may also be interested in:
Stay up-to-date with the latest content from NASA as we explore the universe and discover more about our home planet.
Nighttime Over the Eastern Pacific
2 min read
A long-exposure photo taken from low Earth orbit captured the brilliant illumination coming from airglow, lightning, and stars.
ArticleA Northwest Night Awash in Light
3 min read
The glow of city lights, the aurora, and a rising Moon illuminate the night along the northwest coast of North…
ArticleA Halo Above the Horizon
3 min read
A subtle arc, formed by the bending of light through high-altitude ice crystals, cradles the Moon above the darkened Earth.
Article1
2
3
4
Next
Keep Exploring Discover More from NASA Earth Science Subscribe to Earth Observatory Newsletters
Subscribe to the Earth Observatory and get the Earth in your inbox.
Earth Observatory Image of the Day
NASA’s Earth Observatory brings you the Earth, every day, with in-depth stories and stunning imagery.
Explore Earth Science
Earth Science Data
Massive Computer Simulation Creates a Hyper-Realistic Model of the Milky Way
Research led by the RIKEN Center for Interdisciplinary Theoretical and Mathematical Sciences (iTHEMS) in Japan has successfully performed the world’s first Milky Way simulation that accurately represents more than 100 billion individual stars over the course of 10,000 years.
Galaxies Struggle To Grow In Crowded Environments
New research shows how a galaxy's surroundings influence its development. Its size, shape, and growth rate are all affected. It's all based on "the finer details of the cosmic landscape."
Origin story of domestic cats rewritten by genetic analysis
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The Incredible, Unlikely Story of How Cats Became Our Pets
Two new studies dig into the long, curving path that cats took toward domestication