A total solar eclipse will trace a narrow path across the Arctic and into Europe on Aug. 12, the first total eclipse to reach mainland Europe since 1999, offering millions of people in Greenland, Iceland and northern Spain a chance to witness the moon fully block the sun. The shadow then arcs up and over the North Pole before dropping onto eastern Greenland, crossing the west coast of Iceland near the capital, Reykjavik, and sweeping into northern Spain and a small corner of northwestern Portugal before ending over the Atlantic. In Greenland and Iceland, the sun will darken in the late afternoon or early evening, while in Spain and Portugal, the eclipse won't reach totality until the late evening, shortly before sunset. In Spain, the path of totality will be roughly 290 kilometers, or about 180 miles, wide, making it accessible to a large share of the country's population in the north. Attention going forward is likely to center on weather conditions across Iceland and northern Spain as Aug. 12 approaches, since cloud cover remains the primary risk to visibility along the path.