Weather satellites frequently document dust palls blowing
westward from Africa’s Sahara Desert across the tropical
Atlantic Ocean. Astronauts see these Saharan dust masses as
widespread atmospheric haze. The dust can be transported right
across the Atlantic Ocean, taking about a week to reach North
America (in northern hemisphere summer) or South America (in
northern hemisphere winter). This puts the Caribbean Sea on the
receiving end of many of these events. In the top image, the
margin of hazy air reaches the island of Hispaniola (Haiti and
Dominican Republic) and the Turks and Caicos Islands, though the
eastern tip of Cuba (foreground) remains clear. This image—taken
by astronauts on the International Space Station (ISS) in July
2012—attracted the interest of scientists at NASA’s Johnson
Space Center because the margin between dust haze and clear
atmosphere lies in almost the same location as it appeared in
another astronaut image in July 1994. When astronauts aboard the
Space Shuttle Columbia captured the