Blue Stragglers and the Polarised Universe

Models suggest the Milky Way should have far more dwarf galaxies orbiting it than we see - known as the the "missing satelites" problem.  New evidence suggests a powerful blast of UV radiation my be to blame...

The correct name for this phenomenon is "crepuscular rays". It refers to the apparent spreading out from behind a cloud of sunbeams or shafts of sunlight when you view them from the Earth's surface.

It is, of course, an illusion. The Sun's rays are not issuing from behind a cloud and spreading out towards you: the Sun is so far away that the light rays reaching the Earth are effectively parallel. Instead, this "trick of the light" is caused by perspective. That is, things farther away look smaller. This is why train tracks appear to narrow, or converge, into the distance.

So when you look skywards and see sunbeams coming through a cloud, because the light patches at greater distance appear closer together, making the shafts of light look narrower.

If you've seen a recent 3D film, you'll know that the polarity of light is really important.  Separating different polarities can give us an altogether different view.  The Cosmic Microwave Background is just the same - observing the polarity can tell us about the history of the universe.

Andrew Pontzen speaks to Oxford University's Jo Dunkley...