California wildfires visible from outer space


California's a tinderbox. We feel for the people who are suffering through some of the worst wildfires the region has even seen. The TV drone footage of entire blocks of homes ravaged by fire makes us gasp. We can imagine it happening in our neighborhood as natural catastrophe knows no limits in the long run.

The scope of the fires is plain from Earth orbit as these photos show. They were taken by NASA's Earth-surveying Aqua and Terra satellites which circle the planet every 99 minutes from an altitude of 438 miles. Unlike the space station, which orbits from west to east, Earth surveillance satellites orbit from pole to pole, moving from south to north — or north to south, depending on which side of the globe you live.

During one half of the orbit, the satellite views the daytime side of the Earth. When it reaches the pole, it crosses over to the nighttime side of Earth. Since the planet is rotating below the satellite, Terra and Aqua peer down over the adjacent swath of Earth on their next orbits. In a 24-hour period, polar orbiting satellites view most of the Earth twice, once in daylight and once in darkness.

Because a sun synchronous satellite sees the same piece of ground over and over again under identical lighting conditions (except for variation caused by the seasons) — with the sun in the same part of the sky — they're fantastic for recording changes in land or sea. Scientists can compare images from the same season over several years without worrying that changes in light and shadow will create the illusion of change. You can guess that without satellites in sun-synchronous orbits, it would be impossible to collect the kind of consistent information required to study long-term changes in climate.

Polar orbits are fussy. Gravity pulls on a satellite, shifting its orbit slightly. To maintain a precise track, engineers on the ground have to periodically fire the satellite's thrusters to nudge it back into position. For more satellite wildfire photos and other Earth images from orbit, check out NASA's Earth Observatory page and archive.