English: The constellation of Orion the Hunter, is one of the most familiar sights in the winter sky at night in the northern hemisphere. The image of Orion (above left), with the 3 "belt" stars, the bright blue star Rigel (just below the belt, to the lower right), bright red giant Betelguese (above the belt to the upper left) and the Orion Nebula (the cloudy patch below the belt and to the left) are well-known to earth-bound observers' eyes, sensitive to visible-band radiation. But what does the sky look like to someone like Superman, with eyes sensitive to X-ray radiation? This X-ray view is shown by the image on the left. This image was actually obtained by the ROSAT satellite during the All-Sky Survey phase in 1990-1991. The X-ray image shows the amount of very hot (temperatures greater than 1 million degrees) gas surrounding the stars in the Orion Nebula. This gas is generally heated by shocks as faster moving parcels of gas collide with slower moving parcels, though magnetic heating also plays a role. The X-ray colors represent the temperature of the X-ray emission from each star: hot stars are blue-white and cooler stars are yellow-red. The brightest object in the optical image is the full moon. The full moon is visible in the X-ray image too, but it's much fainter; the brightest X-ray source is the Crab nebula.