Dust is the bane of the optical astronomer's life, blocking the view of many interesting objects. The Universe is full of dust, microscopic particles of varied composition — carbon, silicon, water ice, minerals, frozen carbon monoxide, organic compounds, silicates — the list is almost endless.

The particles can be hard or soft and come in many different shapes, but their size is usually less than 1 micron (one thousandth of a millimetre). The wavelength of visible light is much the same size as many dust particles, so it is easily blocked (scattered) by the dust, whereas longer-wavelength infrared radiation passes through unhindered and dust is therefore transparent to it. And in the far-infrared, we see the 'glow' from dust itself.

The chemical make-up of dust clouds and other interesting regions can be probed by looking at the spectra of their molecules, often only in the infrared. The reason is that most atoms and molecules emit radiation which has energy corresponding to the infrared range (emitted during rotation and vibration). Besides, infrared radiation is typical of cooler regions, for instance dust clouds, where more complex compounds such as organic molecules are often found. Infrared astronomy has made many interesting discoveries related to these more complex molecules in space.

Infrared radiation can help us learn much more about the young‚ distant Universe. The Universe has been expanding since the Big Bang — the event that formed it. There were no stars or galaxies to begin with, but they started to form relatively early. We now know that at half the Universe's present age, star formation was much more vigorous than it is today and that in the very beginning it was zero. So the rate of star formation rate varies in cosmic time. Herschel has been designed to observe infrared-dominated galaxies – which are mostly star-burst galaxies where stars from a thousand times faster than in the Milky Way at present. Herschel will be able to observe these galaxies through the cosmic epochs when most of the stars that ever existed n the Universe formed.