Seeing the invisible
Hubblecast 23. Date- 26th Nov 08. Source- http://www.spacetelescope.org/videos/archive/topic/hubblecast// 'The Universe is a black void, with a scattering of stars, nebulae and galaxies or so it appears to observers using visible light. But if we include other forms of radiation invisible to us, the picture changes completely: clouds of interstellar hydrogen gas, emitting radio waves; stellar nurseries, glowing in the infrared; explosive outbursts of gamma rays and the all-sky background hiss of the Big Bang, diluted by almost fourteen billion years of cosmic expansion. So how do astronomers learn about the unseen Universe? By building telescopes and detectors that can see the invisible. Watch this Hubblecast episode and find out more.'