Follow link for a great BBC video.  Silver sensation seeks cold cosmos

Stare into the curve of Herschel's mirror too long and you get a slightly giddy feeling that comes from not being able to judge where its surface really starts.

It is enchanting, spectacular and - at 3.5m in diameter - it will soon become the biggest telescope mirror in space, surpassing that of Hubble.

The great 18th Century astronomer William Herschel would have been astonished by the silver sensation that now bears his name.

The European Space Agency (Esa) is certainly very proud of its new observatory. It has been working on the venture for more than 20 years.

"The mirror is an enormous piece of hardware," enthused Thomas Passvogel, Esa's programme manager on the Herschel space observatory.

"It's a ceramic mirror; it's the biggest piece ever made from silicon carbide. It's very hard but much, much lighter than glass and the performance is excellent."

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This week, the finished observatory will be flown to Europe's Kourou spaceport in South America. There, it will be bolted to an Ariane rocket and hurled into orbit.

It will take up a vantage point a million-and-a-half kilometres from Earth, to open up what scientists expect to be an utterly fascinating new vista on the Universe.

"Very simply, the science pillars of Herschel are to understand better how stars and galaxies form and how they evolve," Göran Pilbratt, Esa's project scientist on Herschel, told BBC News.

Unlike Hubble, which is tuned to see the cosmos in the same light that is visible to our eyes, Herschel will go after much longer wavelength radiation - in the far-infrared and sub-millimetre range.

It will permit Herschel to see past the dust that scatters Hubble's visible wavelengths, and to gaze at really cold places and objects in the Universe - from the birthing clouds of new stars to the icy comets that live far out in the Solar System.

Some of these targets, though, are frigid in the extreme (between five and 50K; or -268 to -223C); and for Herschel to register them requires an even colder state be achieved on the observatory itself.

This involves the use of a cryostat. It is akin to a giant "thermos" bottle. Filled with more than 2,000 litres of liquid helium, its systems will plunge Herschel's science instruments into the deepest of chills.

Critical detectors will be taken to just fractions of a degree above absolute zero (0K; -273C), from where they can make the most of their remarkable design performance.

"Imagine one million, million, millionth of the brightness of a 60W lightbulb - that's what we can detect with one of our detectors," explained Professor Matt Griffin, who leads the international consortium behind SPIRE (Spectral and Photometric Imaging Receiver), one of Herschel's three instruments.

"Turning that around - imagine observing one of our very faint sources; let's say a very distant galaxy. If we were to observe it with SPIRE for a billion years, we would collect enough energy to light that 60W lightbulb for just one-twentieth of a second," the Cardiff University, UK, researcher said.

Herschel's other instruments are HIFI (the Heterodyne Instrument for the Far Infrared) and PACS (Photodetector Array Camera and Spectrometer).

With the entire package, the observatory can investigate a broad range of wavelengths (55-672 microns), including a swathe that has hitherto been missed by orbiting telescopes.