M74 (also known as NGC 628) is a face-on spiral galaxy located about 24 million light years from Earth in the constellation Pisces. The infrared SPIRE images trace the cold dust between the stars, clearly showing the galaxy’s spiral structure. They also contain many faint dots that are actually distant galaxies. These galaxies contain dust that radiates at infrared wavelengths, but because they are much further away, we cannot see the structure in the galaxies.
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.