Re: Read the paper ...
A beam of light is mad up of a bunch of photons travelling along in the same direction, one after another. Each photon has a magnetic field and an electric field, aligned perpendicularly. If you imagine the photon travelling across your screen from left to right, you might see the magnetic field from the side, so it's a wave drawn on your screen, but if you did then you'd be looking at the electric field from the edge, so it'd be a wave going in and out of your screen. If you then imagine looking at the screen from the right hand side, the photon would be travelling towards you with the magnetic field looking like a vertical line and the electric field looking like a horizontal line. This is the cross that you can see in the polarised light image.
When light's emitted from a source like a star or a hot light bulb, the beams of light/the photons are aligned at random, so if you look at the light source all the photons will look like corsses rotated to random angles.
When you polarise the light, but shining it through a fine grid, polarising sunglasses or a weird quantum phenomenom this forces all the crosses to orient to the same rotation, so you get the polarised light image where all the crosses are like the one you'd see from looking at the side of your monitor.
Interestingly, as you can polarise light to different angles by forcing it through a grid that's rotated to differetn angles, you can convey information in the angle of polarisation. Your light beam could be continuous, pulsed, varying in colour and so on, but you can ignore all of that and look at the polarisation angle to read the information. It's not even effected by blue or red shift. Handy!