Landsat 8, the latest of NASA's Earth-imaging satellites, is set to launch this afternoon. NASA and the US Geological Survey are expected to initiate the launch at 1:02pm EST from California's Vandenberg Air Force Base. Once it's in space, Landsat 8 will collect photographs, thermal data, and infrared images from 438 miles above the surface of the Earth, circling the planet roughly every 99 minutes or 14 times a day. On each pass, the satellite will capture a 185-kilometer-wide section, giving us a full image of the globe once every 16 days. Though it doesn't provide the incredibly high-resolution imagery you'll find in some satellite photos, it gives scientists, businesses, and the public (since the data is released for free) a look at what's going on across the planet, showing us environmental changes or the spread of cities and farmland.
The Landsat program has been running continuously since 1972, and some of its satellites have had incredibly long lifespans: Landsat 5, which was officially retired in December, had been in orbit since 1984. Landsat 7, the most recently launched satellite in the program and the only one currently active, was launched in 1999. Landsat 8 is designed to provide more complete and detailed imagery than previous satellites, with sensors that focus on a single, wide swath of land rather than sweeping across it. It's set for a five-year mission; though that may be extended, it's highly unlikely to last as long as Landsat 5. The launch itself will be streamed on NASA's site, barring last-minute problems that — as with any launch — could delay it.