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You can see it from space!

Massive bushfires are burning in Australia. In order to describe their magnitude, the AP reports that:

The fires were so massive they were visible from space Saturday. NASA released satellite photographs showing a white cloud of smoke across southeastern Australia.

But "you can see it from space!" is a silly way to indicate how big something is -- because we have satellites with very high-resolution cameras that can see some pretty small things. NASA's photo of the smoke plume from the current Victorian fires is impressive, and certainly gives you a sense of their scale. But there's nothing remarkable about the fact that the fires are simply visible at all. The photo the AP got was from MODIS, which has a resolution of up to 250 meters -- fine enough to catch plenty of small fires, some too small to even make the news (perhaps we should say "this fire is so big global news agencies are covering it!"). Here's a global map of fires updated constantly from MODIS data. Some of NASA's other sensors, those aboard Landsat, collect images with a 15 meter resolution. Europe's SPOT satellite can do 2.5 meters. Things don't have to be very big to be visible from space these days.

(On a related note, it's not true that the Great Wall of China is the only human-made object visible from space, or from the moon.)


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