The Chandra satellite normally observes the distant Universe using X-rays (which have far higher energies than the radio waves with which I normally observe galaxies) but scientists using the telescope recently turned it to point at our own planet. They observed the Earth ten times between December 2003 and April 2004 using the High Resolution Camera (HRC) which, if your eye had the same resolution, would let you read a newspapaer at a distance of half a mile! The images below, released yesterday, show what Chandra saw.
Aurora on Earth as seen by the Chandra satellite. The colour represents the intensity of X-ray emission at each point, superimposed on a model of the Earth. CREDIT: NASA/MSFC/CXC/A.Bhardwaj & R.Elsner, et al.; Earth model: NASA/GSFC/L.Perkins & G.Shirah
The bright arcs seen in the observations are regions of X-ray emission generated by auroral activity which we see as the northern or southern lights. Aurora are the result of the interaction of charged particles in the solar wind with the magnetic field and atmosphere of the Earth. The charged particles streaming away from the surface of the Sun are affected by the Earth's magnetic field, causing them to be "channeled" to certain areas of the Earth's atmosphere where they crash into particles in the air emitting the erie light that we see, and the X-rays detected by Chandra. This is not the first time that X-rays have been detected from aurora, the Polar spacecraft also observed this phenomenon, but the X-rays seen by Chandra are at much lower enegies making these observations unique. The press release contains a nice image illustrating the interaction between the solar wind and Earth's magnetic field, how aurora work, and the above pictures in higher resolution.