Confirmation that the universe is flat - expanding at just the right rate not to collapse - came from measurements of ripples in the cosmic background radiation left over from the big bang. Gamma-ray bursts have been one of the hottest topics in astrophysics in the 1990s and earlier this year astronomers found that a new 'softer' type of burst could be connected to supernovae explosions. Extrasolar planets have been another hot topic but until astronomers witnessed the dimming of light from star HD 209458 as it was eclipsed by a planet, all the evidence had been indirect.

In a degenerate fermion gas all the atoms occupy the lowest possible energy states, which leads to radical new quantum statistical properties. Science selected photonic crystals -- structures that can trap and guide specific wavelengths of light -- because of their potential for applications in the IT and telecommunications.

PhysicsWeb will be publish its own top ten highlights of 1999 next week.