Glast will view the sky through "gamma-ray glasses"

While the comic-book Kryptonian had to make do with X-ray vision, Nasa is set to launch a space telescope called Glast which will enable astronomers to view the Universe with "gamma-ray glasses".

Gamma rays are the highest-energy form of light, vastly more energetic than the light we see with our eyes, or even X-rays.

The upper end of this energy range is almost unexplored in astronomy. So the Gamma-ray Large Area Space Telescope will open up a high-energy frontier where important discoveries are almost guaranteed.

If Glast were a piano, it would have about 23 octaves Dr Steven Ritz, Nasa Goddard Space Flight Center

These include massive explosions that release as much energy in a second as the Sun will release over its 10-billion-year lifetime and supermassive black holes that hurl matter vast distances across space at close to the speed of light.

According to Dr Steven Ritz, project scientist for the Glast mission, one of the most interesting things about the gamma-ray sky is that it is always changing.

"If you look up at the night sky, once a decade or so you might see a comet. You might notice that things are moving incredibly slowly. But it looks fairly placid and unchanging," Dr Ritz told BBC News.

WHAT GLAST WILL STUDY Active galaxies and blazars Gamma-ray bursts Neutron stars, including pulsars Cosmic rays Gamma-ray background radiation Dark matter The early Universe

"Supermassive black hole systems are flaring brightly, changing their brightness very quickly. You would see objects pulsating - what we call pulsars."

Dr Dave Thompson, one of the deputy project scientists on Glast, told BBC News: "Our Sun, except when it has a big solar flare, is pretty dim in gamma-rays - almost invisible. So we don't see objects like that. What we do see are things with lots of 'oomph' - lot's of energetic activity."

Historically, Glast follows in the footsteps of another American satellite, the Compton Gamma-Ray Observatory (CGRO). But Glast represents a major step up in capability, covering an incredible range of energy.

"If Glast were a piano, it would have about 23 octaves," explains Dr Ritz.

Dr Thompson adds: "One of the big mysteries left over from the CGRO mission is that half the sources were unidentified - we don't know what they are. That's something we'll be out to solve."

Keeping watch

Gamma-rays are far too energetic to capture in the conventional way. The main scientific instrument on Glast is a telescope without lenses or mirrors: the Large Area Telescope, or Lat. It uses technology adapted from ground-based particle accelerators.

It has 16 so-called tower modules assembled in a four-by-four array. Each tower contains layers of silicon detectors interleaved by thin sheets of tungsten foil.

The gamma-rays are so energetic that when they hit the foil, they are converted into matter, namely an electron and its anti-matter partner the positron. The subsequent paths taken by these particles are tracked by the silicon detectors to reveal where in the sky the gamma-ray came from.

The electron and positron travel down to a calorimeter which measures their energies - and therefore the energy of the original gamma-ray.

Lat's field of view is comparable to the human eye - seeing about 20% of the sky at a time.