SPIRE images of galaxy M74 at three different infrared wavelengths. These wavelengths are the equivalent of blue, green and red colours in the visible spectrum. The images have been processed to bring out the extended structure of the galaxy and to show more detail in the background sky. The image quality is best at 250 microns because all telescopes produce their sharpest images at their shortest wavelengths. By combining the three images, astronomers can measure the properties of the emitting dust and identify the nature of the many distant galaxies that also appear in the pictures.
Herschel’s primary mirror is 3.5 m in diameter, nearly four times larger than any previous infrared space telescope. These images prove that Herschel enables a giant leap forward in our ability to study celestial objects at far infrared wavelengths. NASA’s Spitzer Space Telescope primarily observes infrared wavelengths shorter than Herschel does, so the two telescopes complement each other.